Creating Android App UI Programmatically

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Questions and Answers

What is the first step in modifying the onCreate() method?

Deleting the line that uses a resource layout file for the user interface (correct)

Setting the background of the RelativeLayout view to blue

Adding a RelativeLayout object with a single Button view child

Creating a LayoutParams object to center the button vertically and horizontally

What is the purpose of creating a LayoutParams object?

To add a RelativeLayout object with a single Button view child

To display text that reads “Press Me” on the Button view

To instruct the layout view to place the button in a different location (correct)

To set the background of the RelativeLayout view to blue

What is the final step in adding the Button view to the activity?

Setting the background of the RelativeLayout view to blue

Passing the LayoutParams object through as an argument when adding the child view to the parent (correct)

Creating a LayoutParams object with the appropriate values

Adding some additional rules to the parameters

What is the purpose of adding some additional rules to the parameters?

To instruct the layout parent to center the button vertically and horizontally Signup and view all the answers

What is the result of modifying the onCreate() method?

A RelativeLayout object with a single Button view child is added to the activity Signup and view all the answers

What modification needs to be made to the Button view?

Displaying text that reads “Press Me” on the Button view Signup and view all the answers

What is the primary purpose of overriding the onDraw method in a custom View subclass?

To draw custom graphics on the screen Signup and view all the answers

What is the direction of the y-axis in the Canvas object?

It increases downward Signup and view all the answers

What is the purpose of the Paint object in the Canvas object?

To specify the alpha value and RGB values for drawing Signup and view all the answers

What is the method used to draw a circle in the Canvas object?

drawCircle(centerX, centerY, r, paint) Signup and view all the answers

What is the purpose of using a thread in a custom View subclass?

To update the graphics periodically Signup and view all the answers

What is the method used to fill the window with a color in the Canvas object?

drawARGB(alpha, r, g, b) Signup and view all the answers

What is the data type of the x, y, and r parameters in the drawCircle method?

int Signup and view all the answers

What is the method used to get the dimensions of the drawing area in the Canvas object?

getWidth(), getHeight() Signup and view all the answers

What is the purpose of the setARGB method in the Paint class?

To set the color and transparency of a Paint Signup and view all the answers

What is the Typeface style used to create a bold and italic font?

Typeface.BOLD_ITALIC Signup and view all the answers

How can you create a Typeface from a file in the src/main/assets/ directory?

Typeface.createFromAsset(getAssets(), 'filename') Signup and view all the answers

What is the method used to draw a Bitmap on a Canvas?

canvas.drawBitmap(bmp, 0, 0, null) Signup and view all the answers

What is the purpose of the setTextSize method in the Paint class?

To set the size of the text in a Paint Signup and view all the answers

What is the method used to decode a Bitmap from a resource?

BitmapFactory.decodeResource(getResources(), R.drawable.ID) Signup and view all the answers

What is the purpose of the setStyle method in the Paint class?

To set the style of a Paint to FILL or STROKE Signup and view all the answers

What is the goal of the target exercise?

To display a custom view that draws a 'target' figure Signup and view all the answers

What is the primary benefit of using a Thread in Android?

To enable multi-threading and improve responsiveness Signup and view all the answers

What is the purpose of using a Handler object in Android?

To schedule a task to be executed on the main thread Signup and view all the answers

What is the recommended way to update a View in a separate thread?

By using a Handler object to post a Runnable Signup and view all the answers

What is the purpose of the onTouchEvent method in a custom View class?

To handle finger presses and touch events Signup and view all the answers

What is the requirement for updating the ball in the bouncing ball exercise?

The ball should update 50 times per second Signup and view all the answers

What is the constraint on the ball's velocity in the bouncing ball exercise?

The ball's velocity should be less than 80px per second Signup and view all the answers

What is the purpose of the Looper object in the Handler constructor?

To get a reference to the main thread's Looper Signup and view all the answers

What is the background color of the screen in the bouncing ball exercise?

Yellow Signup and view all the answers

What is the percentage decrease in the size of each consecutive circle?

20% Signup and view all the answers

What is the purpose of calling the invalidate method on a view?

To force a view to redraw itself Signup and view all the answers

What is the primary purpose of using threads in a program?

To implement programs that seem to perform multiple tasks simultaneously Signup and view all the answers

What is the relationship between threads within the same process?

They share data with each other Signup and view all the answers

What is the purpose of the Paint object in the TargetView class?

To set the color of the ovals Signup and view all the answers

What is the effect of the loop in the onDraw method?

It draws multiple ovals on the canvas with decreasing sizes Signup and view all the answers

What is the challenge mentioned in the text?

To introduce a constant to easily change the number of ovals Signup and view all the answers

What is the purpose of the RectF object in the onDraw method?

To define the bounding rectangle of the oval Signup and view all the answers

What is the purpose of the onTouchEvent method in a custom View class?

To process touch events on the screen Signup and view all the answers

What is the return type of the onTouchEvent method?

boolean Signup and view all the answers

What is the purpose of the requestFocus() method in a View constructor?

To receive keyboard events on a device with a keyboard Signup and view all the answers

What is the name of the method used to detect collisions between sprites in a game?

intersects Signup and view all the answers

What is the purpose of the WakeLock?

To prevent the screen from blanking Signup and view all the answers

What is the name of the class used to represent objects of interest in a game?

Sprite Signup and view all the answers

What is the purpose of the onKeyDown method in a custom View class?

To handle key presses on a device with a keyboard Signup and view all the answers

What is the purpose of using a smaller collision rectangle in collision detection?

To give the collisions a bit of slack Signup and view all the answers

What is the primary purpose of overriding the onTouchEvent method in a custom View class?

To handle MotionEvent events Signup and view all the answers

What is the purpose of using a WakeLock?

To prevent screen from blanking Signup and view all the answers

What is the purpose of the onKeyDown method in a custom View class?

To handle keyboard events Signup and view all the answers

What is the primary purpose of the RectF class in Android?

To detect collisions between sprites Signup and view all the answers

What is the primary purpose of the Sprite class in a game?

To represent objects of interest in a game Signup and view all the answers

What is the primary purpose of using a smaller collision rectangle in collision detection?

To give the collisions a bit of slack Signup and view all the answers

What is the name of the method used to detect collisions between sprites in a game?

intersects Signup and view all the answers

What is the primary purpose of the requestFocus method in a View constructor?

To set the focus of the View Signup and view all the answers

What is the primary purpose of the setFocusableInTouchMode method in a View?

To set the focus of the View in touch mode Signup and view all the answers

What is the primary purpose of the onKeyDown/Up methods in a custom View class?

To handle keyboard events Signup and view all the answers

Study Notes

Creating the Example Project in Android Studio

The onCreate() method is initially designed to use a resource layout file for the user interface.
To add views to an activity, the line related to the resource layout file must be deleted from the onCreate() method.

Adding Views to an Activity

A RelativeLayout object with a single Button view child is created programmatically in the onCreate() method.
The Button view is configured to display the text "Press Me".

Setting View Properties

The background of the RelativeLayout view is set to blue.
The Button view is set to display the text "Press Me".

Adding Layout Parameters and Rules

A LayoutParams object is created and initialized with appropriate values to position the button.
The LayoutParams object is used to center the button both horizontally and vertically within the layout.
The LayoutParams object is passed as an argument when adding the child view to the parent.

Drawing 2D Graphics

To draw custom 2D graphics, create a custom View subclass with the drawing code. If the app is animated, use a thread to periodically update the graphics and redraw them.
Use the onDraw method to draw on the view, which is called when the view is redrawn.

Custom View

Create a custom view by extending the View class and overriding the onDraw method.
Insert the custom view into an activity's layout XML.

Canvas Object Methods

drawARGB - fill the window with a color (RGB values: 0-255)
drawArc - draw a partial ellipse
drawBitmap - draw an image
drawCircle - draw a circle
drawLine - draw a line segment
drawOval - draw an oval or circle (Android 5.0 and above)
drawPoint - color a single pixel
drawRect - draw a rectangle (Android 5.0 and above)
drawRoundRect - draw a rounded rectangle (Android 5.0 and above)
drawText - draw a text string
getWidth and getHeight - get the dimensions of the drawing area

Paint

Create a Paint object by specifying an alpha (opacity) value and RGB integer values.
Set the paint style, stroke width, and text size using various methods.
Use the Paint object to set the color, font, and style of the drawn shapes.

Typeface

In Android, a font is called a Typeface.
Set a font inside a Paint object.
Create a Typeface based on a specific font name or a general font family.
Load a Typeface from a file in the assets directory.

Bitmap Images

Draw an image using the Bitmap class.
Decode a Bitmap from a resource using BitmapFactory.decodeResource.
Decode a Bitmap from an input stream using BitmapFactory.decodeStream.

Animation via Redrawing

To animate a view, redraw it at regular intervals and change the variables or positions of the shapes.
Force a view to redraw itself by calling its invalidate method.
Use a thread to redraw the view at regular intervals, but avoid locking up the app's UI.

Threads

A thread is a lightweight process or isolated sub-task within a program.
Use a thread to implement concurrency and perform multiple tasks simultaneously.
Variables created in one thread can be seen by other threads.

Using a Thread

Create a thread by passing a Runnable object with a run method.
Use the start method to start the thread.
Use the stop method to stop the thread.
Use the sleep method to pause the thread.
Use the isRunning method to check if the thread is running.
Use the join method to wait for the thread to finish.

Redrawing a View in a Thread

Use a Handler object to make the invalidate call on the view from the thread.
Create a Handler object and post a Runnable to it to redraw the view.

Mouse Touch Events

Handle finger presses from the user by writing an onTouchEvent method in the custom View class.
Use the getAction method to determine the type of event (e.g., ACTION_DOWN, ACTION_UP, ACTION_MOVE).

Keyboard Events

Handle key presses by setting the app to receive keyboard focus in the View constructor.
Write onKeyDown and onKeyUp methods in the custom View class.
Use the getKeyCode method to determine the key pressed.

Sprite Class

A sprite is an object of interest in a game.
A sprite class can represent the sprites in the game.
The sprite class can contain data such as location, size, velocity, shape/image, and points.

Collision Detection

Collision detection is determining whether sprites in the game world are touching each other.
Use RectF and other shapes to check for collisions using methods such as contains, intersects, and collide.
Use a smaller collision rectangle to give the collisions a bit of slack.

Wake Lock

Use a wake lock to prevent the screen from blanking.

List Adapter Example

An ArrayList is loaded from a file and used to create an ArrayAdapter with the layout android.R.layout.simple_list_item_1.
The adapter is then set to a ListView with the ID mylist.

Handling List Events

List views respond to several events, including setOnItemClickListener, setOnItemLongClickListener, and setOnItemSelectedListener.
Event listeners must be attached in Java code, not in XML, and require the use of anonymous inner classes.

Attaching Event Listeners in Java

Event listeners can be attached using anonymous inner classes, which are declared and constructed on the fly.
An example of attaching an event listener to a button is provided.

List Events

List views respond to several events, including setOnItemClickListener, setOnItemLongClickListener, and setOnItemSelectedListener.
An example of attaching a listener to a ListView is provided, which responds to item clicks.

Anatomy of an Android App and the App Lifecycle

Application Components

Android apps consist of four primary components: Activities, Services, Content Providers, and Broadcast Receivers.
Each component has a different purpose and lifecycle.

Activity

An Activity is a single screen with a user interface, and an app may have several Activities.
Activities are subclasses of the Activity class.

Service

A Service is an application component that performs long-running operations in the background with no UI.
An example of a Service is an app that automatically responds to texts when driving.

Content Providers

A Content Provider is a bridge between applications to share data.
An example of a Content Provider is the device's contacts information.

Broadcast Receivers

A Broadcast Receiver is a component that responds to system-wide announcements.
Examples of broadcasts include battery low, screen off, and date changed.

Intents

Intents are used to pass information between applications.

Activity Stack

The most recently created Activity is at the top of the stack.
When the user presses the Back button or an Activity is destroyed, the previous Activity is brought to the top.

Saving and Restoring State

The onSaveInstanceState method is used to save the state of an Activity.
The onRestoreInstanceState method is used to restore the state of an Activity.

Starting Your Own Activities

New Activities can be started within an Activity to accomplish a task or get some data.
An example of starting a new Activity to get a name is provided.

Drawing 2D Graphics

Custom 2D graphics can be drawn on screen by creating a custom View subclass with the drawing code.
If the app is animated, a thread can be used to periodically update the graphics and redraw them.

Canvas Object Methods

Several methods can be used to draw on a Canvas object, including drawARGB, drawArc, drawBitmap, and more.

Paint

A Paint object can be used to specify a color to use for drawing.
Many methods accept a Paint object as a parameter.

Touch Events

The onTouchEvent method can be overridden to handle touch events.

Keyboard Events

Keyboard events can be handled by setting the app to receive keyboard "focus" in the View constructor.
The onKeyDown and onKeyUp methods can be overridden to handle key presses.

Sprite Class

A Sprite class can be used to represent objects of interest in a game.
Possible data for a Sprite include location, size, velocity, shape/image, and points.

Collision Detection

Collision detection involves determining whether sprites in the game world are touching each other.
Android's RectF and other shapes have methods to check whether they touch.
Collision detection can be more complex for non-rectangular sprites.

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Description

Learn how to add views to an activity in Android Studio by creating a RelativeLayout and Button programmatically in the onCreate() method.

Creating Android App UI Programmatically

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Questions and Answers

What is the first step in modifying the onCreate() method?

What is the purpose of creating a LayoutParams object?

What is the final step in adding the Button view to the activity?

What is the purpose of adding some additional rules to the parameters?

What is the result of modifying the onCreate() method?

What modification needs to be made to the Button view?

What is the primary purpose of overriding the onDraw method in a custom View subclass?

What is the direction of the y-axis in the Canvas object?

What is the purpose of the Paint object in the Canvas object?

What is the method used to draw a circle in the Canvas object?

What is the purpose of using a thread in a custom View subclass?

What is the method used to fill the window with a color in the Canvas object?

What is the data type of the x, y, and r parameters in the drawCircle method?

What is the method used to get the dimensions of the drawing area in the Canvas object?

What is the purpose of the setARGB method in the Paint class?

What is the Typeface style used to create a bold and italic font?

How can you create a Typeface from a file in the src/main/assets/ directory?

What is the method used to draw a Bitmap on a Canvas?

What is the purpose of the setTextSize method in the Paint class?

What is the method used to decode a Bitmap from a resource?

What is the purpose of the setStyle method in the Paint class?

What is the goal of the target exercise?

What is the primary benefit of using a Thread in Android?

What is the purpose of using a Handler object in Android?

What is the recommended way to update a View in a separate thread?

What is the purpose of the onTouchEvent method in a custom View class?

What is the requirement for updating the ball in the bouncing ball exercise?

What is the constraint on the ball's velocity in the bouncing ball exercise?

What is the purpose of the Looper object in the Handler constructor?

What is the background color of the screen in the bouncing ball exercise?

What is the percentage decrease in the size of each consecutive circle?

What is the purpose of calling the invalidate method on a view?

What is the primary purpose of using threads in a program?

What is the relationship between threads within the same process?

What is the purpose of the Paint object in the TargetView class?

What is the effect of the loop in the onDraw method?

What is the challenge mentioned in the text?

What is the purpose of the RectF object in the onDraw method?

What is the purpose of the onTouchEvent method in a custom View class?

What is the return type of the onTouchEvent method?

What is the purpose of the requestFocus() method in a View constructor?

What is the name of the method used to detect collisions between sprites in a game?

What is the purpose of the WakeLock?

What is the name of the class used to represent objects of interest in a game?

What is the purpose of the onKeyDown method in a custom View class?

What is the purpose of using a smaller collision rectangle in collision detection?

What is the primary purpose of overriding the onTouchEvent method in a custom View class?

What is the purpose of using a WakeLock?

What is the purpose of the onKeyDown method in a custom View class?

What is the primary purpose of the RectF class in Android?

What is the primary purpose of the Sprite class in a game?

What is the primary purpose of using a smaller collision rectangle in collision detection?

What is the name of the method used to detect collisions between sprites in a game?

What is the primary purpose of the requestFocus method in a View constructor?

What is the primary purpose of the setFocusableInTouchMode method in a View?

What is the primary purpose of the onKeyDown/Up methods in a custom View class?

Study Notes

Creating the Example Project in Android Studio

Adding Views to an Activity

Setting View Properties

Adding Layout Parameters and Rules

Drawing 2D Graphics

Custom View

Canvas Object Methods

Paint

Typeface

Bitmap Images

Animation via Redrawing

Threads

Using a Thread

Redrawing a View in a Thread

Mouse Touch Events

Keyboard Events

Sprite Class

Collision Detection

Wake Lock