Flutter Chapter 6. PDF

6 Using Common Widgets WHAT YOU WILL LEARN IN THIS CHAPTER How to use basic widgets such as Scaffold, AppBar, SafeArea, Container, Text, RichText, Column, and Row, as well as different types of buttons How to nest the Column and Row widgets together to create different UI layouts...

6 Using Common Widgets WHAT YOU WILL LEARN IN THIS CHAPTER How to use basic widgets such as Scaffold, AppBar, SafeArea, Container, Text, RichText, Column, and Row, as well as different types of buttons How to nest the Column and Row widgets together to create different UI layouts Ways to include images, icons, and decorators How to use text field widgets to retrieve, validate, and manipulate data How to check your app's orientation In this chapter, you'll learn how to use the most common widgets. I call them our base building blocks for creating beautiful UIs and UXs. You'll learn how to load images locally or over the Web via a uniform resource locator (URL), use the included rich Material Components icons, and apply decorators to enhance the look and feel of widgets or use them as input guides to entry fields. You'll also explore how to take advantage of the Form widget to validate text field entry widgets as a group, not just individually. Additionally, to account for the variety of device sizes, you'll see how using the MediaQuery or OrientationBuilder widget is a great way to detect orientation—because using the device orientation and layout widgets accordingly based on portrait or landscape is extremely important. For example, if the device is in portrait mode, you can show a row of three images, but when the device is turned to landscape mode, you can show a row of five images since the width is a larger area than in portrait mode. USING BASIC WIDGETS When building a mobile app, you'll usually implement certain widgets for the base structure. Being familiar with them is necessary. Scaffold As you learned in Chapter 4, “Creating a Starter Project Template,” the Scaffold widget implements the basic Material Design visual layout, allowing you to easily add various widgets such as AppBar, BottomAppBar, FloatingActionButton, Drawer, SnackBar, BottomSheet, and more. AppBar The AppBar widget usually contains the standard title, toolbar, leading, and actions properties (along with buttons), as well as many customization options. title The title property is typically implemented with a Text widget. You can customize it with other widgets such as a DropdownButton widget. leading The leading property is displayed before the title property. Usually this is an IconButton or BackButton. actions The actions property is displayed to the right of the title property. It's a list of widgets aligned to the upper right of an AppBar widget usually with an IconButton or PopupMenuButton. flexibleSpace The flexibleSpace property is stacked behind the Toolbar or TabBar widget. The height is usually the same as the AppBar widget's height. A background image is commonly applied to the flexibleSpace property, but any widget, such as an Icon, could be used. SafeArea The SafeArea widget is necessary for today's devices such as the iPhone X or Android devices with a notch (a partial cut‐out obscuring the screen usually located on the top portion of the device). The SafeArea widget automatically adds sufficient padding to the child widget to avoid intrusions by the operating system. You can optionally pass a minimum amount of padding or a Boolean value to not enforce padding on the top, bottom, left, or right. Container The Container widget is a commonly used widget that allows customization of its child widget. You can easily add properties such as color, width, height, padding, margin, border, constraint, alignment, transform (such as rotating or sizing the widget), and many others. The child property is optional, and the Container widget can be used as an empty placeholder (invisible) to add space between widgets. Text The Text widget is used to display a string of characters. The Text constructor takes the arguments string, style, maxLines, overflow, textAlign, and others. A constructor is how the arguments are passed to initialize and customize the Text widget. RichText The RichText widget is a great way to display text using multiple styles. The RichText widget takes TextSpans as children to style different parts of the strings. Column A Column widget displays its children vertically. It takes a children property containing an array of List, meaning you can add multiple widgets. The children align vertically without taking up the full height of the screen. Each child widget can be embedded in an Expanded widget to fill the available space. CrossAxisAlignment, MainAxisAlignment, and MainAxisSize can be used to align and size how much space is occupied on the main axis. Row A Row widget displays its children horizontally. It takes a children property containing an array of List. The same properties that the Column contains are applied to the Row widget with the exception that the alignment is horizontal, not vertical. Buttons There are a variety of buttons to choose from for different situations such as RaisedButton, FloatingActionButton, FlatButton, IconButton, PopupMenuButton, and ButtonBar. TRY IT OUT Adding AppBar Widgets Create a new Flutter project and name it ch6_basics; you can follow the instructions in Chapter 4. For this project, you need to create only the pages folder. The goal of this app is to provide a look at how to use the basic widgets, not necessarily to design the best‐looking UI. In Chapter 10, “Building Layouts,” you'll focus on building complex and beautiful layouts. 1. Open the main.dart file. Change the primarySwatch property from blue to lightGreen. primarySwatch: Colors.lightGreen, 2. Open the home.dart file. Start by customizing the AppBar widget properties. 3. Add to the AppBar a leadingIconButton. If you override the leading property, it is usually an IconButton or BackButton.  leading: IconButton( icon: Icon(Icons.menu), onPressed: () { }, ), 4. The title property is usually a Text widget, but it can be customized with other widgets such as a DropdownButton. By following the instructions from Chapter 4, you have already added the Text widget to the title property; if not, add the Text widget with a value of 'Home'. title: Text('Home'), 5. The actions property takes a list of widgets; add two IconButton widgets. actions: [ IconButton( icon: Icon(Icons.search), onPressed: () {}, ), IconButton( icon: Icon(Icons.more_vert), onPressed: () {}, ), ], 6. Because you are using an Icon for the flexibleSpace property, let's add a SafeArea and an Icon as a child. flexibleSpace: SafeArea( child: Icon( Icons.photo_camera, size: 75.0, color: Colors.white70, ), ), 7. Add a PreferredSize for the bottom property with a Container for a child. bottom: PreferredSize( child: Container( color: Colors.lightGreen.shade100, height: 75.0, width: double.infinity, child: Center( child: Text('Bottom'), ), ), preferredSize: Size.fromHeight(75.0), ),  How It Works You learned how to customize the AppBar widget by using widgets to set the title, toolbar, leading, and actions properties. All the properties that you learned about in this example are related to customizing the AppBar. In Chapter 9, “Creating Scrolling Lists and Effects” you'll learn to use the SliverAppBar widget, which is an AppBar embedded in a sliver using a CustomScrollView, making any app come to life with pinpoint customizations such as parallax animation. I absolutely love using slivers because they add an extra layer of customization. In the next section, you'll learn how to customize the Scaffoldbody property by nesting widgets to build the page content. SafeArea The SafeArea widget is a must for today's devices such as the iPhone X or Android devices with a notch (a partial cut‐out obscuring the screen usually located on the top portion of the device). The SafeArea widget automatically adds sufficient padding to the child widget to avoid intrusions by the operating system. You can optionally pass minimum padding or a Boolean value to not enforce padding on the top, bottom, left, or right. TRY IT OUT Adding a SafeArea to the Body Continue modifying the home.dart file. Add a Padding widget to the body property with a SafeArea as a child. Because this example packs in different uses of widgets, add a SingleChildScrollView as a child of the SafeArea. The SingleChildScrollView allows the user to scroll and view hidden widgets; otherwise, the user sees a yellow and black bar conveying that the widgets are overflowing. body: Padding( padding: EdgeInsets.all(16.0), child: SafeArea( child: SingleChildScrollView( child: Column( children: [ ], ), ), ), ), Sample Wrap Widget Tip There is a great way to wrap a current widget as a child of another widget. Place your cursor on top of the current widget to wrap and then press Option+Enter on your keyboard. The Dart/quick assist pops up. Choose the Wrap with new widget option. Do not add the following steps to your project; this is a tip on how to quickly wrap a widget with another. 1. Place the cursor on the widget to wrap. 2. Press Option+Enter (Alt+Enter in Windows). The Dart/quick assist pops up.  3. Select a Wrap with new widget option such as body:widget(child:Container()),. 4. Rename the widget to SafeArea and notice that child: is automatically the Container() widget. Make sure you add a comma after the Container() widget, as shown here. Placing a comma after every property ensures correct Flutter formatting over multiple lines. body: SafeArea(child: Container(),), How It Works Adding the SafeArea widget automatically adjusts padding for devices that have a notch. Any SafeAreachild widgets are constrained to the correct padding. Container The Container widget has an optional child widget property and can be used as a decorated widget with a custom border, color, constraint, alignment, transform (such as rotating the widget), and more. This widget can be utilized as an empty placeholder (invisible), and if a child is omitted, it sizes to the full available screen size. TRY IT OUT Adding a Container Continue modifying the home.dart file. Since you want to keep your code readable and manageable, you'll create widget classes to build each body widget section of the Column list of widgets. 1. Add to the body property a Padding widget with the child property set to a SafeArea widget. Add to the SafeAreachild a SingleChildScrollView. Add to the SingleChildScrollViewchild a Column. For the Columnchildren, add the call to the ContainerWithBoxDecorationWidget() widget class, which you will create next. Make sure the widget class uses the const keyword to take advantage of caching (performance). body: Padding( padding: EdgeInsets.all(16.0), child: SafeArea( child: SingleChildScrollView( child: Column( children: [ const ContainerWithBoxDecorationWidget(), ], ), ), ), ), 2. Create the ContainerWithBoxDecorationWidget() widget class after classHomeextendsStatelessWidget{…}. The widget class will return a Widget. Note that when you refactor by creating widget classes, they are of type StatelessWidget unless you specify to use a StatefulWidget. class ContainerWithBoxDecorationWidget extends StatelessWidget { const ContainerWithBoxDecorationWidget({ Key key, }) : super(key: key); @override  Widget build(BuildContext context) { return Column( children: [ Container(), ], ); } } 3. Start adding properties to the Container by adding a height of175.0 pixels. Note the comma after the number, which separates properties and helps to keep the Dart code formatted. Go to the next line to add the decoration property, which accepts a BoxDecoration class. The BoxDecoration class provides different ways to draw a box, and in this case, you are adding a BorderRadius class to the bottomLeft and bottomRight of the Container. Container( height: 100.0, decoration: BoxDecoration(), ), 4. Using the named constructor BorderRadius.only() allows you to control the sides to draw round corners. I purposely made the bottomLeft radius much bigger than the bottomRight to show the custom shapes you can create. BoxDecoration( borderRadius: BorderRadius.only( bottomLeft: Radius.circular(100.0), bottomRight: Radius.circular(10.0), ), ), The BoxDecoration also supports a gradient property. You are using a LinearGradient, but you could also have used a RadialGradient. The LinearGradient displays the gradient colors linearly, and the RadialGradient displays the gradient colors in a circular manner. The begin and end properties allow you to choose the start and end positions for the gradient by using the AlignmentGeometry class. AlignmentGeometry is a base class for Alignment that allows direction‐aware resolution. You have many directions to choose from such as Alignment.bottomLeft, Alignment.centerRight, and more. begin: Alignment.topCenter, end: Alignment.bottomCenter, The colors property requires a List of Color types, List. The list of Colors is entered within square brackets separated by commas. colors: [ Colors.white, Colors.lightGreen.shade500, ], Here's the full gradient property source code: gradient: LinearGradient( begin: Alignment.topCenter, end: Alignment.bottomCenter, colors: [ Colors.white, Colors.lightGreen.shade500, ], ), 5. The boxShadow property is a great way to customize a shadow, and it takes a list of BoxShadows, called List. For the BoxShadow, set the color, blurRadius, and offset properties. boxShadow: [ BoxShadow( color: Colors.white, blurRadius: 10.0, offset: Offset(0.0, 10.0), ) ], The last part of the Container is to add a child Text widget wrapped by a Center widget. The Center widget allows you to center the child widget on the screen. child: Center( child: Text('Container'), ), 6. Add a Center widget as a child of the Container, and add to the Center widget child a Text widget with the string Container. (In the next section, I'll go over the Text widget in detail.) child: Center( child: Text('Container'), ), Here's the full ContainerWithBoxDecorationWidget() widget class source code: class ContainerWithBoxDecorationWidget extends StatelessWidget { const ContainerWithBoxDecorationWidget({ Key key, }) : super(key: key); @override Widget build(BuildContext context) { return Column( children: [ Container( height: 100.0, decoration: BoxDecoration( borderRadius: BorderRadius.only( bottomLeft: Radius.circular(100.0), bottomRight: Radius.circular(10.0), ), gradient: LinearGradient( begin: Alignment.topCenter, end: Alignment.bottomCenter, colors: [ Colors.white, Colors.lightGreen.shade500,  ], ), boxShadow: [ BoxShadow( color: Colors.grey, blurRadius: 10.0, offset: Offset(0.0, 10.0), ), ], ), child: Center( child: RichText( text: Text('Container'), ), ), ], ); } } How It Works Containers can be powerful widgets full of customization. By using decorators, gradients, and shadows, you can create beautiful UIs. I like to think of containers as enhancing an app in the same way a great‐looking frame adds to a painting. Text You've already used the Text widget in the preceding examples; it's an easy widget to use but also customizable. The Text constructor takes the arguments string, style, maxLines, overflow, textAlign, and others. Text( 'Flutter World for Mobile', style: TextStyle( fontSize: 24.0, color: Colors.deepPurple, decoration: TextDecoration.underline, decorationColor: Colors.deepPurpleAccent, decorationStyle: TextDecorationStyle.dotted, fontStyle: FontStyle.italic, fontWeight: FontWeight.bold, ), maxLines: 4, overflow: TextOverflow.ellipsis, textAlign: TextAlign.justify, ), RichText The RichText widget is a great way to display text using multiple styles. The RichText widget takes TextSpan as children to style different parts of the strings (Figure 6.1). FIGURE 6.1: RichText with TextSpan TRY IT OUT Replacing Text with a RichText Child Container Instead of using the previous ContainerText widget to show a plain‐text property, you can use a RichText widget to enhance and emphasize the words in your string. You can change each word's color and styles. 1. Find the Container child Text widget and delete Text('Container'). child: Center( child: Text('Container'), ), 2. Replace the Container child's Text widget with a RichText widget. The RichTexttext property is a TextSpan object (class) that is customized by using a TextStyle for the style property. The TextSpace has a children list of TextSpan where you place different TextSpan objects to format different portions of the entire RichText. By using the RichText widget and combining different TextSpan objects, you create rich‐text formatting like with a word processor. child: Center( child: RichText( text: TextSpan( text: 'Flutter World', style: TextStyle( fontSize: 24.0, color: Colors.deepPurple, decoration: TextDecoration.underline, decorationColor: Colors.deepPurpleAccent, decorationStyle: TextDecorationStyle.dotted, fontStyle: FontStyle.italic, fontWeight: FontWeight.normal, ),  children: [ TextSpan( text: ' for', ), TextSpan( text: ' Mobile', style: TextStyle( color: Colors.deepOrange, fontStyle: FontStyle.normal, fontWeight: FontWeight.bold), ), ], ), ), ), How It Works RichText is a powerful widget when combined with the TextSpan object (class). There are two main parts to styling, the default text property and the children list of TextSpan. The text property using a TextSpan sets the default styling for the RichText. The children list of TextSpan allows you to use multiple TextSpan objects to format different strings. Column A Column widget (Figures 6.2 and 6.3) displays its children vertically. It takes a children property containing an array of List. The children align vertically without taking up the full height of the screen. Each child widget can be embedded in an Expanded widget to fill available space. You can use CrossAxisAlignment, MainAxisAlignment, and MainAxisSize to align and size how much space is occupied on the main axis. FIGURE 6.2: Column widget FIGURE 6.3: Column widget rendered in app Column( crossAxisAlignment: CrossAxisAlignment.center, mainAxisAlignment: MainAxisAlignment.spaceEvenly, mainAxisSize: MainAxisSize.max, children: [ Text('Column 1'), Divider(), Text('Column 2'), Divider(), Text('Column 3'), ], ), Row A Row widget (Figures 6.4 and 6.5) displays its children horizontally. It takes a children property containing an array of List. The same properties that the Column contains are applied to the Row widget with the exception that the alignment is horizontal, not vertical. FIGURE 6.4: Row widget FIGURE 6.5: Row widget rendered in app Row( crossAxisAlignment: CrossAxisAlignment.start, mainAxisAlignment: MainAxisAlignment.spaceEvenly, mainAxisSize: MainAxisSize.max, children: [  Row( children: [ Text('Row 1'), Padding(padding: EdgeInsets.all(16.0),), Text('Row 2'), Padding(padding: EdgeInsets.all(16.0),), Text('Row 3'), ], ), ], ), Column and Row Nesting A great way to create unique layouts is to combine Column and Row widgets for individual needs. Imagine having a journal page with Text in a Column with a nested Row containing a list of images (Figures 6.6 and 6.7). FIGURE 6.6: Column and Row nesting FIGURE 6.7: Column and Row widgets rendered in app Add a Row widget inside the Column widget. Use mainAxisAlignment:MainAxisAlignment.spaceEvenly and add three Text widgets. Column( crossAxisAlignment: CrossAxisAlignment.start, mainAxisAlignment: MainAxisAlignment.spaceEvenly, mainAxisSize: MainAxisSize.max, children: [ Text('Columns and Row Nesting 1',), Text('Columns and Row Nesting 2',), Text('Columns and Row Nesting 3',), Padding(padding: EdgeInsets.all(16.0),), Row( mainAxisAlignment: MainAxisAlignment.spaceEvenly, children: [ Text('Row Nesting 1'), Text('Row Nesting 2'), Text('Row Nesting 3'), ], ), ], ), TRY IT OUT Adding Column, Row, and Nesting the Row and Column together as Widget Classes You'll add three widget classes to the body property section of the Column list of widgets. Between each widget class, you'll add a simple Divider() widget to draw separation lines between sections. 1. Add the widget class names ColumnWidget(), RowWidget(), and ColumnAndRowNestingWidget() to the Column children widget list. The Column widget is located in the body property. Add a Divider() widget between each widget class name. Make sure each widget class uses the const keyword. body: Padding( padding: EdgeInsets.all(16.0), child: SafeArea( child: SingleChildScrollView( child: Column( children: [ const ContainerWithBoxDecorationWidget(), Divider(), const ColumnWidget(), Divider(), const RowWidget(), Divider(), const ColumnAndRowNestingWidget(), ], ), ), ), ), 2. Create the ColumnWidget() widget class after the ContainerWithBoxDecorationWidget() widget class. class ColumnWidget extends StatelessWidget { const ColumnWidget({ Key key, }) : super(key: key);  @override Widget build(BuildContext context) { return Column( crossAxisAlignment: CrossAxisAlignment.center, mainAxisAlignment: MainAxisAlignment.spaceEvenly, mainAxisSize: MainAxisSize.max, children: [ Text('Column 1'), Divider(), Text('Column 2'), Divider(), Text('Column 3'), ], ); } } 3. Create the RowWidget() widget class after the ColumnWidget() widget class. class RowWidget extends StatelessWidget { const RowWidget({ Key key, }) : super(key: key); @override Widget build(BuildContext context) { return Row( crossAxisAlignment: CrossAxisAlignment.start, mainAxisAlignment: MainAxisAlignment.spaceEvenly, mainAxisSize: MainAxisSize.max, children: [ Row( children: [ Text('Row 1'), Padding(padding: EdgeInsets.all(16.0),), Text('Row 2'), Padding(padding: EdgeInsets.all(16.0),), Text('Row 3'), ], ), ], ); } }  4. Create the ColumnAndRowNestingWidget() widget class after the RowWidget() widget class. class ColumnAndRowNestingWidget extends StatelessWidget { const ColumnAndRowNestingWidget({ Key key, }) : super(key: key); @override Widget build(BuildContext context) { return Column( crossAxisAlignment: CrossAxisAlignment.start, mainAxisAlignment: MainAxisAlignment.spaceEvenly, mainAxisSize: MainAxisSize.max, children: [ Text('Columns and Row Nesting 1',), Text('Columns and Row Nesting 2',), Text('Columns and Row Nesting 3',), Padding(padding: EdgeInsets.all(16.0),), Row( mainAxisAlignment: MainAxisAlignment.spaceEvenly, children: [ Text('Row Nesting 1'), Text('Row Nesting 2'), Text('Row Nesting 3'), ], ), ], ); } } How It Works Column and Row are handy widgets to lay out either vertically or horizontally. Nesting the Column and Row widgets creates flexible layouts needed for each circumstance. Nesting widgets is at the heart of designing Flutter UI layouts. Buttons There are a variety of buttons to choose from, depending on the situation, such as FloatingActionButton, FlatButton, IconButton, RaisedButton, PopupMenuButton, and ButtonBar. FloatingActionButton The FloatingActionButton widget is usually placed on the bottom right or center of the main screen in the ScaffoldfloatingActionButton property. Use the FloatingActionButtonLocation widget to either dock (notch) or float above the navigation bar. To dock a button to the navigation bar, use the BottomAppBar widget. By default, it's a circular button but can be customized to a stadium shape by using the named constructor FloatingActionButton.extended. In the example code, I commented out the stadium shape button for you to test. floatingActionButtonLocation: FloatingActionButtonLocation.endDocked, floatingActionButton: FloatingActionButton( onPressed: () {}, child: Icon(Icons.play_arrow), backgroundColor: Colors.lightGreen.shade100, ), // or // This creates a Stadium Shape FloatingActionButton // floatingActionButton: FloatingActionButton.extended( // onPressed: () {}, // icon: Icon(Icons.play_arrow), // label: Text('Play'), // ), bottomNavigationBar: BottomAppBar( hasNotch: true, color: Colors.lightGreen.shade100, child: Row( mainAxisAlignment: MainAxisAlignment.spaceEvenly, children: [ Icon(Icons.pause), Icon(Icons.stop), Icon(Icons.access_time), Padding( padding: EdgeInsets.all(32.0), ), ],  ), ), Figure 6.8 shows the FloatingActionButton widget on the bottom right of the screen with the notch enabled. FIGURE 6.8: FloatingActionButton with notch FlatButton The FlatButton widget is the most minimalist button used; it displays a text label without any borders or elevation (shadow). Since the text label is a widget, you could use an Icon widget instead or another widget to customize the button. color, highlightColor, splashColor, textColor, and other properties can be customized. // Default - left button FlatButton( onPressed: () {}, child: Text('Flag'), ), // Customize - right button FlatButton( onPressed: () {}, child: Icon(Icons.flag), color: Colors.lightGreen, textColor: Colors.white, ), Figure 6.9 shows the default FlatButton widget on the left and the customized FlatButton widget on the right. FIGURE 6.9: FlatButton RaisedButton The RaisedButton widget adds a dimension, and the elevation (shadow) increases when the user presses the button. // Default - left button RaisedButton( onPressed: () {}, child: Text('Save'), ), // Customize - right button RaisedButton( onPressed: () {}, child: Icon(Icons.save), color: Colors.lightGreen, ), Figure 6.10 shows the default RaisedButton widget on the left and the customized RaisedButton widget on the right. FIGURE 6.10: RaisedButton IconButton The IconButton widget uses an Icon widget on a Material Component widget that reacts to touches by filling with color (ink). The combination creates a nice tap effect, giving the user feedback that an action has started. // Default - left button IconButton( onPressed: () {}, icon: Icon(Icons.flight), ), // Customize - right button IconButton( onPressed: () {}, icon: Icon(Icons.flight), iconSize: 42.0, color: Colors.white, tooltip: 'Flight', ), Figure 6.11 shows the default IconButton widget on the left and the customized IconButton widget on the right. FIGURE 6.11: IconButton PopupMenuButton The PopupMenuButton widget displays a list of menu items. When a menu item is pressed, the value passes to the onSelected property. A common use of this widget is placing it on the top right of the AppBar widget for the user to select different menu options. Another example is to place the PopupMenuButton widget in the middle of the AppBar widget showing a list of search filters. TRY IT OUT Creating the PopupMenuButton and the Items' Class and List Before you add the PopupMenuButton widgets, let's create the Class and List necessary to build the items to be displayed. Usually, the TodoMenuItem (model) class would be created in a separate Dart file, but to keep the example focused, you'll add it to the home.dart file. In the final three chapters of this book, you'll separate classes into their own files. 1. Create a TodoMenuItem class. When you create this class, make sure it's not inside another class. Create the class and list at the end of the file after the last closing curly bracket, }. The TodoMenuItem class contains a title and an icon. class TodoMenuItem { final String title; final Icon icon; TodoMenuItem({this.title, this.icon}); } 2. Create a List of TodoMenuItem. This List will be called foodMenuList and will contain a List (array) of TodoMenuItems. // Create a List of Menu Item for PopupMenuButton List foodMenuList = [ TodoMenuItem(title: 'Fast Food', icon: Icon(Icons.fastfood)), TodoMenuItem(title: 'Remind Me', icon: Icon(Icons.add_alarm)), TodoMenuItem(title: 'Flight', icon: Icon(Icons.flight)), TodoMenuItem(title: 'Music', icon: Icon(Icons.audiotrack)), ]; 3. Create a PopupMenuButton. You will use an itemBuilder to build the List of TodoMenuItems. If you do not set an icon for the PopupMenuButton, a default menu icon is used by default. The onSelected will retrieve the item selected on the list. Use the itemBuilder to build a list of foodMenuList and map to TodoMenuItem. A PopupMenuItem is returned for each item in the foodMenuList. For the PopupMenuItem child, you use a Row widget to show the Icon and Text widgets together. PopupMenuButton( icon: Icon(Icons.view_list), onSelected: ((valueSelected) { print('valueSelected: ${valueSelected.title}'); }), itemBuilder: (BuildContext context) { return foodMenuList.map((TodoMenuItem todoMenuItem) { return PopupMenuItem( value: todoMenuItem, child: Row( children: [ Icon(todoMenuItem.icon.icon), Padding(padding: EdgeInsets.all(8.0),), Text(todoMenuItem.title), ], ), ); }).toList(); }, ),  4. Modify the AppBarbottom property by adding the widget class name: PopupMenuButtonWidget(). bottom: PopupMenuButtonWidget(), 5. Create the PopupMenuButtonWidget() widget class after the ColumnAndRowNestingWidget() widget class. Since the bottom property is expecting a PreferredSizeWidget, you use the keyword implementsPreferredSizeWidget in the class declaration. The class extends the StatelessWidget and implements the PreferredSizeWidget. After the widget build, implement the @overridepreferredSize getter; this is a required step because the purpose of PreferredSizeWidget is to provide the size for the widget; in this example, you'll set the height property. Without this step, we'd have no size specified. @override // implement preferredSize Size get preferredSize => Size.fromHeight(75.0); The following is the entire PopupMenuButtonWidget widget class. Note that the Container widget's height property uses the preferredSize.height property that you set in the PreferredSizeWidget getter. class PopupMenuButtonWidget extends StatelessWidget implements PreferredSizeWidget { const PopupMenuButtonWidget({ Key key, }) : super(key: key); @override Widget build(BuildContext context) { return Container( color: Colors.lightGreen.shade100, height: preferredSize.height, width: double.infinity, child: Center( child: PopupMenuButton( icon: Icon(Icons.view_list), onSelected: ((valueSelected) { print('valueSelected: ${valueSelected.title}'); }), itemBuilder: (BuildContext context) { return foodMenuList.map((TodoMenuItem todoMenuItem) { return PopupMenuItem( value: todoMenuItem, child: Row( children: [ Icon(todoMenuItem.icon.icon), Padding( padding: EdgeInsets.all(8.0), ), Text(todoMenuItem.title), ], ), ); }).toList(); }, ), ), ); } @override // implement preferredSize  Size get preferredSize => Size.fromHeight(75.0); } How It Works The PopupMenuButton widget is a great widget to display a List of items such as menu choices. For the list of items, you created a TodoMenuItemClass to hold a title and icon. You created the foodMenuList, which is a List of each TodoMenuItem. In this case, the List items are hard‐coded, but in a real‐world app, the values can be read from a web service. In Chapters 14, 15 and 16, you'll implement Cloud Firestore to access data from a web server. ButtonBar The ButtonBar widget (Figure 6.12) aligns buttons horizontally. In this example, the ButtonBar widget is a child of a Container widget to give it a background color. FIGURE 6.12: ButtonBar Container( color: Colors.white70, child: ButtonBar( alignment: MainAxisAlignment.spaceEvenly, children: [ IconButton( icon: Icon(Icons.map), onPressed: () {},  ), IconButton( icon: Icon(Icons.airport_shuttle), onPressed: () {}, ), IconButton( icon: Icon(Icons.brush), onPressed: () {}, ), ], ), ), TRY IT OUT Adding Buttons as Widget Classes You've looked at the FloatingActionButton, FlatButton, RaisedButton, IconButton, PopupMenuButton, and ButtonBar widgets. Here you'll create two widget classes to organize the buttons' layout. 1. Add the widget class names ButtonsWidget() and ButtonBarWidget() to the Column children widget list. The Column is located in the body property. Add a Divider() widget between each widget class name. Make sure each widget class uses the const keyword. body: Padding( padding: EdgeInsets.all(16.0), child: SafeArea( child: SingleChildScrollView( child: Column( children: [ const ContainerWithBoxDecorationWidget(), Divider(), const ColumnWidget(), Divider(), const RowWidget(), Divider(), const ColumnAndRowNestingWidget(), Divider(), const ButtonsWidget(), Divider(), const ButtonBarWidget(), ], ), ), ), ), 2. Create the ButtonsWidget() widget class after the ColumnAndRowNestingWidget() widget class. The class returns a Column with three Row widgets for the children list of Widget. Each Rowchildren list of Widget contains different buttons such as the FlatButton, RaisedButton, and IconButton buttons. class ButtonsWidget extends StatelessWidget { const ButtonsWidget({ Key key, }) : super(key: key); @override Widget build(BuildContext context) { return Column( children: [ Row( children: [ Padding(padding: EdgeInsets.all(16.0)), FlatButton( onPressed: () {}, child: Text('Flag'), ), Padding(padding: EdgeInsets.all(16.0)), FlatButton( onPressed: () {}, child: Icon(Icons.flag), color: Colors.lightGreen, textColor: Colors.white, ), ], ), Divider(), Row( children: [ Padding(padding: EdgeInsets.all(16.0)), RaisedButton( onPressed: () {}, child: Text('Save'), ), Padding(padding: EdgeInsets.all(16.0)), RaisedButton( onPressed: () {}, child: Icon(Icons.save), color: Colors.lightGreen, ), ], ), Divider(), Row(  children: [ Padding(padding: EdgeInsets.all(16.0)), IconButton( icon: Icon(Icons.flight), onPressed: () {}, ), Padding(padding: EdgeInsets.all(16.0)), IconButton( icon: Icon(Icons.flight), iconSize: 42.0, color: Colors.lightGreen, tooltip: 'Flight', onPressed: () {}, ), ], ), Divider(), ], ); } } 3. Create the ButtonBarWidget() widget class after the ButtonsWidget() widget class. The class returns a Container with a ButtonBar as a child. The ButtonBarchildren list of Widget contains three IconButton widgets. class ButtonBarWidget extends StatelessWidget { const ButtonBarWidget({ Key key, }) : super(key: key); @override Widget build(BuildContext context) { return Container( color: Colors.white70, child: ButtonBar( alignment: MainAxisAlignment.spaceEvenly, children: [ IconButton( icon: Icon(Icons.map), onPressed: () {}, ), IconButton( icon: Icon(Icons.airport_shuttle), onPressed: () {},  ), IconButton( icon: Icon(Icons.brush), highlightColor: Colors.purple, onPressed: () {}, ), ], ), ); } } How It Works The FloatingActionButton, FlatButton, RaisedButton, IconButton, PopupMenuButton, and ButtonBar widgets are configurable by setting the properties icon, iconSize, tooltip, color, text, and more. USING IMAGES AND ICONS Images can make an app look tremendous or ugly depending on the quality of the artwork. Images, icons, and other resources are commonly embedded in an app. AssetBundle The AssetBundle class provides access to custom resources such as images, fonts, audio, data files, and more. Before a Flutter app can use a resource, you must declare it in the pubspec.yaml file. // pubspec.yaml file to edit # To add assets to your application, add an assets section, like this: assets: —assets/images/logo.png —assets/images/work.png —assets/data/seed.json Instead of declaring each asset, which can get very long, you can declare all the assets in each directory. Make sure you end the directory name with a forward slash, /. Throughout the book, I'll use this approach when adding assets to the projects. // pubspec.yaml file to edit # To add assets to your application, add an assets section, like this: assets: —assets/images/ —assets/data/ Image The Image widget displays an image from a local or URL (web) source. To load an Image widget, there are a few different constructors to use. Image()—Retrieves image from an ImageProvider class Image.asset()—Retrieves image from an AssetBundle class using a key Image.file()—Retrieves image from a File class Image.memory()—Retrieves image from a Uint8List class Image.network()—Retrieves image from a URL path Press Ctrl+Spacebar to invoke the code completion for the available options (Figure 6.13). FIGURE 6.13: Image code completion As a side note, the Image widget also supports animated GIFs. The following sample uses the default Image constructor to initialize the image and fit arguments. The image argument is set by using the AssetImage() constructor with the default bundle location of the logo.png file. You can use the fit argument to size the Image widget with the BoxFit options, such as contain, cover, fill, fitHeight, fitWidth, or none (Figure 6.14). FIGURE 6.14: Images loaded locally and from network (web) // Image - on the left side Image( image: AssetImage("assets/images/logo.png"), fit: BoxFit.cover, ), // Image from a URL - on the right side Image.network( 'https://flutter.io/images/catalog-widget-placeholder.png', ), If you add color to the image, it colorizes the image portion and leaves any transparencies alone, giving a silhouette look (Figure 6.15). FIGURE 6.15: Silhouette‐style image // Image Image( image: AssetImage("assets/images/logo.png"), color: Colors.deepOrange, fit: BoxFit.cover, ), Icon The Icon widget is drawn with a glyph from a font described in IconData. Flutter's icons.dart file has the full list of icons available from the font MaterialIcons. A great way to add custom icons is to add to the AssetBundle fonts containing glyphs. Once example is Font Awesome, which has a high‐quality list of icons and a Flutter package. Of course, there are many other high‐quality icons available from other sources. The Icon widget allows you to change the Icon widget's color, size, and other properties (Figure 6.16). FIGURE 6.16: Icons with custom sizes Icon( Icons.brush, color: Colors.lightBlue, size: 48.0, ), TRY IT OUT Creating the Images Project; Adding Assets; and Loading Images, Icons, and Decorators Create a new Flutter project and name it ch6_images; you can follow the instructions in Chapter 4. For this project, you need to create only the pages and assets/images folders. Create the Home class as a StatelessWidget. The goal of this app is to provide a look at how to use the Image and Icon widgets. In this example, you'll customize the width property of the two Image widgets according to the device screen size. To obtain the device screen size, you can use the MediaQuery.of() method. 1. Open the pubspec.yaml file to add resources. In the assets section, add the assets/images/ folder declaration. I like to create an assets folder at the root of the project and add subfolders for each type of resource, as shown in Chapter 4. # To add assets to your application, add an assets section, such as this: assets: - assets/images/ Add the folder assets and subfolder images at the project's root and then copy the logo.png file to the images folder. Click the Save button, and depending on the editor you are using, it automatically runs flutterpackagesget. Once finished, it shows this message: Processfinishedwithexitcode0. If it does not automatically run the command for you, open the Terminal window (located at the bottom of your editor) and type flutter packages get. 2. Open the home.dart file and modify the body property. Add a SafeArea widget to the body property with a SingleChildScrollView as a child of the SafeArea widget. Add Padding as a child of SingleChildScrollView and then add a Column as a child of the Padding.  body: SafeArea( child: SingleChildScrollView( child: Padding( padding: EdgeInsets.all(16.0), child: Column( children: [ ], ), ), ), ), 3. Add the widget class name ImagesAndIconWidget() to the Column children widget list. The Column is located in the body property. body: SafeArea( child: SingleChildScrollView( child: Padding( padding: EdgeInsets.all(16.0), child: Column( children: [ const ImagesAndIconWidget(), ], ), ), ), ), 4. Add the ImagesAndIconWidget() widget class after classHomeextendsStatelessWidget{…}. In the widget class, a local image is loaded by the AssetImage class. Using the Image.network constructor an image is loaded by a URL string. The Image widget's width property uses the MediaQuery.of(context).size.width/3 to calculate the width value as one‐third of the device width. class ImagesAndIconWidget extends StatelessWidget { const ImagesAndIconWidget({ Key key, }) : super(key: key); @override Widget build(BuildContext context) {  return Row( mainAxisAlignment: MainAxisAlignment.spaceEvenly, children: [ Image( image: AssetImage("assets/images/logo.png"), //color: Colors.orange, fit: BoxFit.cover, width: MediaQuery.of(context).size.width / 3, ), Image.network( 'https://flutter.io/images/catalog-widget- placeholder.png', width: MediaQuery.of(context).size.width / 3, ), Icon( Icons.brush, color: Colors.lightBlue, size: 48.0, ), ], ); } } How It Works By declaring your assets in the pubspec.yaml file, they are accessible by the AssetImage class from an AssetBundle. The Image widget through the image property loads a local image with the AssetBundle class. To load an image over a network (such as the Web), you use the Image.network constructor by passing a URL string. The Icon widget uses the MaterialIcons font library, which draws a glyph from the font described in the IconData class. USING DECORATORS Decorators help to convey a message depending on the user's action or customize the look and feel of a widget. There are different types of decorators for each task. Decoration—The base class to define other decorations.  BoxDecoration—Provides many ways to draw a box with border, body, and boxShadow. InputDecoration—Used in TextField and TextFormField to customize the border, label, icon, and styles. This is a great way to give the user feedback on data entry, specifying a hint, an error, an alert icon, and more. A BoxDecoration class (Figure 6.17) is a great way to customize a Container widget to create shapes by setting the borderRadius, color, gradient, and boxShadow properties. FIGURE 6.17: BoxDecoration applied to a Container // BoxDecoration Container( height: 100.0, width: 100.0, decoration: BoxDecoration( borderRadius: BorderRadius.all(Radius.circular(20.0)), color: Colors.orange, boxShadow: [ BoxShadow( color: Colors.grey, blurRadius: 10.0, offset: Offset(0.0, 10.0), ) ], ), ), The InputDecoration class (Figure 6.18) is used with a TextField or TextFormField to specify labels, borders, icons, hints, errors, and styles. This is helpful in communicating with the user as they enter data. For the border property shown here, I am implementing two ways to customize it, with UnderlineInputBorder and with OutlineInputBorder: FIGURE 6.18: InputDecoration with OutlineInputBorder and default border // TextField TextField( keyboardType: TextInputType.text, style: TextStyle( color: Colors.grey.shade800, fontSize: 16.0, ), decoration: InputDecoration( labelText: "Notes", labelStyle: TextStyle(color: Colors.purple), //border: UnderlineInputBorder(), border: OutlineInputBorder(), ), ), // TextFormField TextFormField( decoration: InputDecoration( labelText: 'Enter your notes', ), ), TRY IT OUT Continuing the Images Project by Adding Decorators Still editing the home.dart file, you'll add the BoxDecoratorWidget() and InputDecoratorsWidget() widget classes. 1. Add the widget class names BoxDecoratorWidget() and InputDecoratorsWidget() after the ImagesAndIconWidget() widget class. Add a Divider() widget between each widget class name. body: SafeArea( child: SingleChildScrollView( child: Padding( padding: EdgeInsets.all(16.0), child: Column( children: [ const ImagesAndIconWidget(), Divider(), const BoxDecoratorWidget(), Divider(), const InputDecoratorsWidget(), ], ), ), ), ), 2. Add the BoxDecoratorWidget() widget class after the ImagesAndIconWidget() widget class. The widget class returns a Padding widget with the Container widget as a child. The Containerdecoration property uses the BoxDecoration class. Using the BoxDecorationborderRadius, color, and boxShadow properties, you create a rounded button shape such as the one in Figure 6.17. class BoxDecoratorWidget extends StatelessWidget { const BoxDecoratorWidget({  Key key, }) : super(key: key); @override Widget build(BuildContext context) { return Padding( padding: EdgeInsets.all(16.0), child: Container( height: 100.0, width: 100.0, decoration: BoxDecoration( borderRadius: BorderRadius.all(Radius.circular(20.0)), color: Colors.orange, boxShadow: [ BoxShadow( color: Colors.grey, blurRadius: 10.0, offset: Offset(0.0, 10.0), ) ], ), ), ); } } 3. Add the InputDecoratorsWidget() widget class after the BoxDecoratorWidget() widget class. You take a TextField and use TextStyle to change the color and fontSize properties. The InputDecoration class is used to set the labelText, labelStyle, border, and enabledBorder values to customize the border properties. I am using the OutlineInputBorder here, but you could also use the UnderlineInputBorder class instead. I left borderUnderlineInputBorder and enabledBorderOutlineInputBorder() commented out, allowing you to test both classes. The following code adds two TextField widgets customized by two different decorations. The first TextField customizes different InputDecoration properties to show a purple notes label with the OutlineInputBorder(). The second TextField widget uses the decoration without customizing the border property. class InputDecoratorsWidget extends StatelessWidget { const InputDecoratorsWidget({ Key key, }) : super(key: key); @override Widget build(BuildContext context) { return Column( children: [ TextField( keyboardType: TextInputType.text, style: TextStyle( color: Colors.grey.shade800, fontSize: 16.0, ), decoration: InputDecoration( labelText: "Notes", labelStyle: TextStyle(color: Colors.purple), //border: UnderlineInputBorder(), //enabledBorder: OutlineInputBorder(borderSide: BorderSide(color.Colors.purple)), border: OutlineInputBorder(), ), ), Divider( color: Colors.lightGreen, height: 50.0, ), TextFormField( decoration: InputDecoration(labelText: 'Enter your notes'), ), ], ); } } How It Works Decorators are invaluable to enhance the look and feel of widgets. The BoxDecoration provides many ways to draw a box with border, body, and boxShadow. The InputDecoration is used in either a TextField or TextFormField. Not only does it allow the customization of the border, label, icon, and styles, but it also gives users feedback on data entry with hints, errors, icons, and more. USING THE FORM WIDGET TO VALIDATE TEXT FIELDS There are different ways to use text field widgets to retrieve, validate, and manipulate data. The Form widget is optional, but the benefits of using a Form widget are to validate each text field as a group. You can group TextFormField widgets to manually or automatically validate them. The TextFormField widget wraps a TextField widget to provide validation when enclosed in a Form widget. If all text fields pass the FormStatevalidate method, then it returns true. If any text fields contain errors, it displays the appropriate error message for each text field, and the FormStatevalidate method returns false. This process gives you the ability to use FormState to check for any validation errors instead of checking each text field for errors and not allowing the posting of invalid data. The Form widget needs a unique key to identify it and is created by using GlobalKey. This GlobalKey value is unique across the entire app. In the next example, you'll create a form with two TextFormFields (Figure 6.19) to enter an item and quantity to order. You'll create an Order class to hold the item and quantity and fill the order once the validation passes. FIGURE 6.19: The Form and TextFormField layout TRY IT OUT Creating the Form Validation App Create a new Flutter project and name it ch6_form_validation. You can follow the instructions in Chapter 4. For this project, you need to create only the pages folder. The goal of this app is to show how to validate data entry values. 1. Open the home.dart file and add to the body a SafeArea widget with Column as a child. In the Column children, add the Form() widget, which you modify in step 7. body: SafeArea( child: Column( children: [ Form(), ], ), ), 2. Create the Order class after class_HomeStateextendsState{…}. The Order class will hold item as a String value and quantity as an int value. class _HomeState extends State { //… } class Order { String item; int quantity; } 3. After the class_HomeStateextendsState declaration and before @override, add the variables _formStateKey for the GlobalKey value and _order to initiate the Order class. Create the unique key for the form by using GlobalKey and mark it final since it will not change.  class _HomeState extends State { final GlobalKey _formStateKey = GlobalKey(); // Order to Save Order _order = Order(); 4. Create the _validateItemRequired(Stringvalue) method that accepts a String value. Use the ternary operator to check whether the value is set to isEmpty, and if yes, then return 'ItemRequired'. Otherwise, return null. String _validateItemRequired(String value) { return value.isEmpty ? 'Item Required' : null; } 5. Create the _validateItemCount(Stringvalue) method that accepts a String value. Use the ternary operator to convert String to int. Then check whether int is greater than zero; if it's not, return 'AtleastoneItemisRequired'. String _validateItemCount(String value) { // Check if value is not null and convert to integer int _valueAsInteger = value.isEmpty ? 0 : int.tryParse(value); return _valueAsInteger == 0 ? 'At least one Item is Required' : null; } 6. Create the _submitOrder() method called by the FlatButton widget to check whether all TextFormField fields pass validation and call Formsave() to gather values from all TextFormFields to the Order class. void _submitOrder() { if(_formStateKey.currentState.validate()) { _formStateKey.currentState.save(); print('Order Item: ${order.item}'); print('Order Quantity: ${order.quantity}'); } }  7. Add to the Form() widget a private key variable called _formStateKey, set autovalidate to true, add Padding for the child property, and add Column as a child of Padding. Setting autovalidate to true allows the Form() widget to check validation for all fields as the user enters information and to display an appropriate message. If autovalidate is set to false, no validation happens until the _formStateKey.currentState.validate() method is manually called. Form( key: _formStateKey, autovalidate: true, child: Padding( padding: EdgeInsets.all(16.0), child: Column( children: [ ], ), ), ), 8. Add two TextFormField widgets to the Columnchildren list of Widget. The first TextFormField is an item description, and the second TextFormField is a quantity of items to order. 9. Add an InputDecoration class with hintText and labelText for each TextFormField. hintText: 'Espresso', labelText: 'Item', 10. Add a call for the validator and onSaved methods. The validator method is called to validate characters as they are entered, and the onSaved method is called by the Formsave() method to gather values from each TextFormField. For the validator, pass the value entered in the TextFormField widget by naming the variable value inside parentheses and use the fat arrow syntax (=>) to call the  method _validateItemRequired(value). The fat arrow syntax is shorthand for {returnmycustomexpression;}. validator: (value) => _validateItemRequired(value), Note that in step 2 you created an Order class to hold the item and quantity values to be collected by the onSaved methods. When the Formsave() method is called, all of the TextFieldFormonSaved methods are called, and values are collected in the Order class such as order.item=value. onSaved: (value) => order.item = value, The following code shows both TextFormFields: TextFormField( decoration: InputDecoration( hintText: 'Espresso', labelText: 'Item', ), validator: (value) => _validateItemRequired(value), onSaved: (value) => order.item = value, ), TextFormField( decoration: InputDecoration( hintText: '3', labelText: 'Quantity', ), validator: (value) => _validateItemCount(value), onSaved: (value) => order.quantity = int.tryParse(value), ), Notice that you use int.tryParse() to convert the quantity value from String to int. 11. Add a Divider and a RaisedButton after the last TextFormField. For the onPressed, call the _submitOrder() method created in step 6. Divider(height: 32.0,), RaisedButton( child: Text('Save'), color: Colors.lightGreen,  onPressed: () => _submitOrder(), ), How It Works When retrieving data from input fields, the Form widget is an incredible helper, and you used the GlobalKey class to assign a unique key to identify it. Use the Form widget to group TextFormField widgets to manually or automatically validate them. The FormStatevalidate method validates data, and if it passes, it returns true. If the FormStatevalidate method fails, it returns false, and each text field displays the appropriate error message. Each TextFormField validator property has a method to check for the appropriate value. Each TextFormFieldonSaved property passes the currently entered value to the Order class. In a real‐world app, you would take the Order class values and save them to a database locally or on a web server. In Chapters 14, 15 and 16, you'll learn how to implement Cloud Firestore to access data from a web server. CHECKING ORIENTATION Under certain scenarios, knowing the device orientation helps in laying out the appropriate UI. There are two ways to figure out orientation, MediaQuery.of(context).orientation and OrientationBuilder. A huge note on OrientationBuilder: it returns the amount of space available to the parent to figure out orientation. This means it does not guarantee the actual device orientation. I prefer using MediaQuery to obtain the actual device orientation because of its accuracy. TRY IT OUT Creating the Orientation App Create a new Flutter project and name it ch6_orientation. You can follow the instructions in Chapter 4. For this project, you only need to create the pages folder. In this example, the UI layout will change depending on orientation. When the device is in portrait mode, it will show one Icon, and when in landscape mode, it will show two Icons. You'll take a look at a Container widget that will grow in size and change color, and you'll use a GridView widget to show two or four columns. Lastly, I added the OrientationBuilder widget to show that when the OrientationBuilder is not a parent widget, the correct orientation is not calculated correctly. But if you place the OrientationBuilder as a parent, it works correctly; note that using SafeArea does not affect the outcome. The following image shows the final project. 1. Open the home.dart file and add to the body a SafeArea with SingleChildScrollView as a child. Add Padding as a child of the SingleChildScrollView. Add a Column as a child of the Padding. In the Columnchildren property, add the widget class called OrientationLayoutIconsWidget(), which you will create next. Make sure you add the const keyword before the widget class name to take advantage of caching to improve performance. body: SafeArea( child: SingleChildScrollView( child: Padding( padding: EdgeInsets.all(16.0), child: Column( children: [ const OrientationLayoutIconsWidget(), ], ), ), ), ), 2. Add the OrientationLayoutIconsWidget() widget class after classHomeextendsStatelessWidget{…}. The first variable to initialize is the current orientation by calling MediaQuery.of() after Widgetbuild(BuildContextcontext). class OrientationLayoutIconsWidget extends StatelessWidget { const OrientationLayoutIconsWidget({ Key key, }) : super(key: key); @override Widget build(BuildContext context) { Orientation _orientation = MediaQuery.of(context).orientation; return Container(); } } 3. Based on the current Orientation, you return a different layout of Icon widgets. Use a ternary operator to check whether Orientation is portrait, and if so, return a single Row icon. If Orientation is landscape, return a Row of two Icon widgets. Replace the current returnContainer() with the following code: return _orientation == Orientation.portrait ? Row( mainAxisAlignment: MainAxisAlignment.center, children: [ Icon( Icons.school, size: 48.0, ), ], ) : Row( mainAxisAlignment: MainAxisAlignment.center, children: [ Icon( Icons.school, size: 48.0, ), Icon( Icons.brush, size: 48.0, ), ], ); 4. Putting all of the code together, you get the following: class OrientationLayoutIconsWidget extends StatelessWidget { const OrientationLayoutIconsWidget({ Key key, }) : super(key: key); @override Widget build(BuildContext context) { Orientation _orientation = MediaQuery.of(context).orientation; return _orientation == Orientation.portrait ? Row(  mainAxisAlignment: MainAxisAlignment.center, children: [ Icon( Icons.school, size: 48.0, ), ], ) : Row( mainAxisAlignment: MainAxisAlignment.center, children: [ Icon( Icons.school, size: 48.0, ), Icon( Icons.brush, size: 48.0, ), ], ); } } 5. After OrientationLayoutIconsWidget(), add a Divider widget and the OrientationLayoutWidget() widget class to create. The steps are similar to the earlier ones, but instead of using rows and icons, you are using containers: obtain the Orientation mode and for portrait return a yellow Container widget with a width of 100.0 pixels. When the device is rotated, the landscape returns a green Container widget with a width of 200.0 pixels.  class OrientationLayoutWidget extends StatelessWidget { const OrientationLayoutWidget({ Key key, }) : super(key: key); @override Widget build(BuildContext context) { Orientation _orientation = MediaQuery.of(context).orientation; return _orientation == Orientation.portrait ? Container( alignment: Alignment.center, color: Colors.yellow, height: 100.0, width: 100.0, child: Text('Portrait'), ) : Container( alignment: Alignment.center, color: Colors.lightGreen, height: 100.0, width: 200.0, child: Text('Landscape'), ); } } 6. After OrientationLayoutWidget(), add a Divider widget and the GridViewWidget() widget class that you will create. Although you will take a closer look at the GridView widget in Chapter 9, it is appropriate to use it now since it's the closest to a real‐world example. In portrait mode, the GridView widget shows two columns, and in landscape mode, it shows four columns. There are a few items to note here. Since the GridView widget is inside a Column widget, set the GridView.count constructorshrinkWrap argument to true or it will break the constraints. I also set the physics argument to NeverScrollableScrollPhysics() or the GridView will scroll its children from within. Remember, you have all these widgets inside a SingleChildScrollView.  class GridViewWidget extends StatelessWidget { const GridViewWidget({ Key key, }) : super(key: key); @override Widget build(BuildContext context) { Orientation _orientation = MediaQuery.of(context).orientation; return GridView.count( shrinkWrap: true, physics: NeverScrollableScrollPhysics(), crossAxisCount: _orientation == Orientation.portrait ? 2 : 4, childAspectRatio: 5.0, children: List.generate(8, (int index) { return Text("Grid $index", textAlign: TextAlign.center,); }), ); } } 7. After GridViewWidget(), add a Divider widget and the OrientationBuilderWidget() widget class that you will create. As mentioned previously, I use MediaQuery.of() to obtain orientation because it's more accurate, but it's good to know how to use OrientationBuilder. OrientationBuilder requires a builder property to be passed and cannot be null. The builder property takes two parameters: BuildContext and Orientation. builder: (BuildContext context, Orientation orientation) {} The steps and result are the same as with _buildOrientationLayout(). Use the ternary operator to check for the orientation, and for portrait, and return a yellow Container widget with a width of 100.0 pixels. When the device is rotated, the landscape returns a green Container widget with a width of 200.0 pixels. Note that OrientationBuilder runs the risk of not detecting the orientation mode correctly because it is a child widget and relies on the parent screen size instead of the device orientation. Because of this, I recommend using MediaQuery.of() instead. // OrientationBuilder as a child does not give correct Orientation. i.e Child of Column… // OrientationBuilder as a parent gives correct Orientation class OrientationBuilderWidget extends StatelessWidget { const OrientationBuilderWidget({ Key key, }) : super(key: key); @override Widget build(BuildContext context) { return OrientationBuilder( builder: (BuildContext context, Orientation orientation) { return orientation == Orientation.portrait ? Container( alignment: Alignment.center, color: Colors.yellow, height: 100.0, width: 100.0, child: Text('Portrait'), ) : Container( alignment: Alignment.center, color: Colors.lightGreen, height: 100.0, width: 200.0, child: Text('Landscape'), ); }, ); } }  How It Works You can detect device orientation by calling MediaQuery.of(context).orientation, which returns either a portrait or landscape value. There is also OrientationBuilder, which returns the amount of space available to the parent to figure out the orientation. I recommend using MediaQuery to retrieve the correct device orientation. SUMMARY In this chapter, you learned about the most commonly used (basic) widgets. These basic widgets are the building blocks to designing mobile apps. You also explored different types of buttons to choose depending on the situation. You learned how to add assets to your app via AssetBundle by listing items in the pubspec.yaml file. You used the Image widget to load images from the local device or a web server through a URL string. You saw how the Icon widget gives you the ability to load icons by using the MaterialIcons font library. To modify the appearance of widgets, you learned how to use BoxDecoration. To improve giving users feedback on data entry, you implemented InputDecoration. Validating multiple text field data entries can be cumbersome, but you can use the Form widget to manually or automatically validate them. Lastly, using MediaQuery to find out the current device orientation is extremely powerful in any mobile app to lay out widgets depending on the orientation. In the next chapter, you'll learn how to use animations. You'll start by using widgets such as AnimatedContainer, AnimatedCrossFade, and AnimatedOpacity and finish with the powerful AnimationController for custom animation. WHAT YOU LEARNED IN THIS CHAPTER TOPIC KEY CONCEPTS Using You learned to use Scaffold, SafeArea, AppBar, basic Container, Text, RichText, Column, Row, Column and widgets RowNesting, Buttons, FloatingActionButton, FlatButton, RaisedButton, IconButton, PopupMenuButton, and ButtonBar. Using You learned to use AssetBundle, Image, and Icon. images Using You learned to use Decoration, BoxDecoration, and decorators InputDecoration. Using You learned to use the Form widget to validate each forms for TextFormField as a group. text field validation Detecting You learned to use MediaQuery.of(context).orientation orientation and OrientationBuilder to detect device orientation.