ASP.NET Web Forms: Building Interactive Web Apps

• ASP.NET is a web development platform that provides a programming model, software infrastructure, and services for building robust web applications for PC and mobile devices.
• It operates on top of the HTTP protocol, utilizing HTTP commands and policies for browser-to-server communication and cooperation.
• ASP.NET is part of the Microsoft .NET platform, using compiled code based on extensible and reusable components in the .NET framework.
• Application codes can be written in C#, Visual Basic.Net, JScript, or J#.
• It creates interactive, data-driven web applications using controls like text boxes, buttons, and labels to generate HTML pages.

ASP.Net Web Forms Model

• ASP.Net web forms extend the event-driven interaction model to web applications.
• The browser sends a web form to the web server, in response the server returns a full markup or HTML page.
• All client-side user activities are sent to the server for stateful processing.
• The server manages the output of client actions and initiates reactions.
• The ASP.Net framework helps store application state information, consisting of page state and session state.
• Page state refers to the client's state, showing content in various input fields in the web form.
• Session state refers to the collective data from various pages a user has visited and interacted with, representing the overall session state.

Shopping Cart Example

• In the example of a shopping cart, a user adds items, and the total collected items and price are displayed on the cart page.
• HTTP alone cannot track information across pages.
• ASP.Net session state and server-side infrastructure track information globally during a session.
• The ASP.Net runtime transfers the page state to and from the server during page requests, incorporates server-side component states in hidden fields.

ASP.Net Component Model

• Provides building blocks for ASP.Net pages as an object model.
• Server-side counterparts of HTML elements/tags such as <form> and <input>
• Also server controls, help develop user interfaces like the Calendar or Gridview control

ASP.NET Technology and .Net Framework

• ASP.NET is a technology working on the .Net framework, which houses all web-related functionalities
• The .Net framework has an object-oriented hierarchy.
• When a user requests an ASP.NET page, the IIS delegates processing to the ASP.NET runtime system.
• The ASP.NET runtime converts a .aspx page into an instance of a class inheriting from the base class Page of the .Net framework. Each element becomes an object.

Components of .Net Framework 3.5:

• Common Language Runtime (CLR): Manages memory, handles exceptions, provides debugging, manages security, handles thread execution, ensures code safety, and provides verification/compilation.
  • Codes are managed by the CLR are managed code. The source code is converted into CPU-independent intermediate language (IL) code and compiled into native code by a Just-in-Time (JIT) compiler, which is CPU-specific
• .Net Framework Class Library: Contains a vast library of reusable types, classes, interfaces, structures, and enumerated values, collectively called types.
• Common Language Specification: Contains Specifications for .Net supported languages and language integration implementation
• Common Type System: Provides guidelines for declaring, using and managing types at runtime, and cross-language communication.
• Metadata and Assemblies: Metadata is binary information describing a program stored in a portable executable file (PE) or memory. Assembly is a unit consisting of the assembly manifest, type metadata, IL code, and resources such as image files.
• Windows Forms: The graphical representation of any window displayed in an application.
• ASP.Net and ASP.Net AJAX: ASP.Net is a web development model, and AJAX is an extension for developing and implementing AJAX functionality. ASP.Net AJAX enables developers to update website data without a full page reload.
• ADO.Net: Used for working with data and databases, provides access to SQL Server, OLE DB, and XML. It connects to data sources for data retrieval, data manipulation and data updating.
• Windows Workflow Foundation (WF): Used for building workflow-based applications in Windows. It provides workflow designer, workflow runtime, activities and a rules engine.
• Windows Presentation Foundation: Separates the user interface and business logic, supporting visually stunning interfaces with documents, media, 2D/3D graphics, and animations.
• Windows Communication Foundation (WCF): Utilized for building and running connected systems.
• Windows CardSpace: Provides safety and security for accessing resources and sharing personal information online.
• LINQ: Adds data querying capabilities to .Net languages, similar to SQL.

Server-Side Controls - Button Controls

• ASP.Net offers three types of button controls: Buttons, Link Buttons, and Image Buttons, the Image Button displays an image, a link button uses text that looks like a hyperlink, and a Button control displays text within a rectangular area.
• When a user clicks a button control, Click and Command events are triggered.
• Basic syntax: <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Click" />
• Text: The text displayed on the button, applicable for button and link button controls only.
• ImageUrl: Path to the image for image button controls.
• AlternateText: Text to display for image button controls if the image is unavailable.
• CausesValidation: Determines if page validation checks occur when a user clicks the button; default value is true.
• CommandName: A string value passed to the Command event when a user clicks the button.
• CommandArgument: A string value passed to the Command event when a user clicks the button.
• PostBackUrl: The web page URL requested when the user clicks the button.

Server-Side Controls - Text Boxes and Labels:

• Text box controls typically accept user input and can handle one or more lines of text based on the TextMode attribute.
• Label controls display text and can be changed from page execution. Text does not change if literal text is used.
• Basic syntax: <asp:TextBox ID="txtstate" runat="server"></asp:TextBox>
• TextMode: Specifies the type of text box, where SingleLine enables a standard text box, MultiLine enables a box that can accept more than one line of text, and Password replaces entered characters with asterisks. SingleLine set as default.
• Text: The content of the text box
• MaxLength: The maximum number of characters accepted in the text box.
• Wrap: Determines whether the text automatically wraps for multi-line inputs. Default set to true
• ReadOnly: determines whether the user can alter the text in the box, default value is false, user cannot change.
• Columns: The width of the text box based on the characters, with the actual width based on the font used.
• Rows: The height of a multi-line text box in lines, with a default value of 0 creating a single-line text box.
• For label, the most used attribute is ‘Text’.

Check Boxes and Radio Buttons:

• Check boxes provide a single option. Users can either check or uncheck. Radio buttons present a group, user can select only one option.
• To group Radio buttons assign them them same GroupName attribute. Use different group names to create multiple groups.
• To select a check box or radio button when the form initially appear. Set the Checked attribute to true. When multiple radio buttons have the Checked attribute set in the same group, only the last will be selected.
• Basic syntax for a check box: <asp:CheckBox ID= "chkoption" runat="Server"></asp:CheckBox>
• Basic syntax for a radio button: <asp:RadioButton ID= "rdboption" runat="Server"></asp: RadioButton>
• Common Properties of the Check Boxes and Radio Buttons are: Text & GroupName
• Text: The text displayed for the buttons.
• Checked: To specify if it is selected, default value is set to false.
• GroupName: The group that the control belongs to.

List Controls

• ASP.NET provides the following controls: Drop-Down List, List Box, Radio Button List, Check Box List, Bulleted List.
• List Boxes and Drop-Down Lists contain one or more List items which can be loaded using code or ListItem Collection editor.
• Basic Syntax of List Box Control: <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged"></asp:DropDownList>

Common Properties of the List Box and Drop-Down Lists are:

• Items is the collection of the list item objects and returns an object.
• Rows specifies the number of items displayed in the box. Scroll bar is added if the actual list contents has more rows.
• SelectedIndex is the index of the current selected item.
• SelectedValue is the value of the currently selected item. If no item is selected, results in an empty string.
• SelectionMode Indicates that the list box allows a single or multiple selection.
• The SelectedIndexChanged event is raised when the user selects a different item from the drop-down list or list box.
• To work with a Drop-Down List/List Box item, the Items property is used, it contains all the list items.
• ListItemCollection is a collection of ListItem Objects, each object represents one item on the list. List items are numbered from 0. If loaded using strings like Istcolor.Items.Add("Blue") then the text and value properties of list items are identical.

The ListItemCollection Editor

• Allows for static list items to be added in a Drop-Down list/List Box. Displayed by selecting Edit Item on the smart tag. Or selecting the control and clicking the ellipsis button from the Item property of properties window.
• Item(integer) is a ListIterm object, it represents the item.
• Count is property that is the number of items in the collection.
• Add(string) method adds a new item at the end of the collection and assigns the string parameter to the text property item
• Add(listItem) method adds a new item at the end of the collection
• Insert(integer, String), inserts an item on the specified index location to the collection and assigns the text property item to the string parameter
• Insert(integer, ListIterm), inserts the item at the specified index location to the collection
• Remove(String) method, removes the item that is same as the string provided
• Remove(listItem) removes the specified item
• RemoveAt(integer) removes the item at the specific index integer
• Clear() removes all the items in the collection
• FindByValue(string) returns the item that has the same value
• FindByValue(text) returns the item that has the same string

Radio Button List and Check Box List.

• Radio button list presents a list of mutually exclusive options. The check box list offers a list of independent options. Controls contain a collection of ListItem, referred to in the Items property.
• Basic Syntax for radio button list: <asp:RadioButtonList ID="RadioButtonList1" runat="server" AutoPostBack="True" OnSelectedIndexChanged="RadioButtonList1_SelectedIndexChanged"></asp:RadioButtonList>
• Basic Syntax for check box list: <asp:CheckBoxList ID="CheckBoxList1" runat="server" AutoPostBack="True" OnSelectedIndexChanged="CheckBoxList1_SelectedIndexChanged"></asp:CheckBoxList>

Common properties of check boxes and radio lists are:

• RepeatLayout Attribute specifies whether to use normal HTML flow or Table tags while formatting the list when rendered. Default is Table.
• RepeatDirection Attribute specifies the direction of the controls to be repeated, with Vertical and Horizontal options. Default is Vertical.
• RepeatColumns specifies the number of columns to use for repeating the controls. Default is 0.
• Bulleted List Control Creates bulleted lists or numbered list items. Controls contain a collection of ListItem objects that can be referred to through the Items property.
• Basic Syntax of Bulleted List is <asp:BulletedList ID="BulletedList1" runat="server"></asp:BulletedList>
• BulletStyle Property specifies style, and bullets.
• HyperLink Control is like HTML element. Basic syntax is <asp:HyperLink ID="HyperLink1" runat="server"> HyperLink </asp:HyperLink>
• Properties of hyperlink control : ImageUrl, NavigateUrI, Target and Text.
• Image Control is used for displaying images. Basic Syntax is <asp:Image ID="Image1" runat="server">
• Properties are AlternateText, ImageAlign and ImageURL.