ASP.NET Web Forms: List Control

ASP.NET List Controls are used to display lists of items in various formats, either as a simple list or a more complex template-based list.

1. Simple List Controls

Simple list controls provide basic list functionality for displaying options, allowing users to select single or multiple items.

DropDownList: Displays a dropdown list of items, allowing a single selection.

Example:

<asp:DropDownList ID="DropDownList1" runat="server">
    <asp:ListItem Text="Option 1" Value="1"></asp:ListItem>
    <asp:ListItem Text="Option 2" Value="2"></asp:ListItem>
</asp:DropDownList>

ListBox: Displays a list of items, allowing multiple selections.

Example:

<asp:ListBox ID="ListBox1" runat="server" SelectionMode="Multiple">
    <asp:ListItem Text="Option 1" Value="1"></asp:ListItem>
    <asp:ListItem Text="Option 2" Value="2"></asp:ListItem>
</asp:ListBox>

RadioButtonList: Displays a group of radio buttons, where only one can be selected.

Example:

<asp:RadioButtonList ID="RadioButtonList1" runat="server">
    <asp:ListItem Text="Option 1" Value="1"></asp:ListItem>
    <asp:ListItem Text="Option 2" Value="2"></asp:ListItem>
</asp:RadioButtonList>

CheckBoxList: Displays a group of checkboxes, where multiple selections are allowed.

Example:

<asp:CheckBoxList ID="CheckBoxList1" runat="server">
    <asp:ListItem Text="Option 1" Value="1"></asp:ListItem>
    <asp:ListItem Text="Option 2" Value="2"></asp:ListItem>
</asp:CheckBoxList>

2. Template List Controls

Template list controls allow for a more customizable display of list items using templates to define the appearance and behavior of each item.

Repeater: Displays a repeated list of items using templates without built-in paging or sorting capabilities.

Example:

<asp:Repeater ID="Repeater1" runat="server">
    <ItemTemplate>
        <div><%# Eval("ItemName") %></div>
    </ItemTemplate>
</asp:Repeater>

DataList: Similar to the Repeater, but allows for a table-based layout with more built-in features like paging and selection.

Example:

<asp:DataList ID="DataList1" runat="server">
    <ItemTemplate>
        <div><%# Eval("ItemName") %></div>
    </ItemTemplate>
</asp:DataList>

GridView: Displays tabular data with features like sorting, paging, and editing.

Example:

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="True">
</asp:GridView>

ASP.NET Validation Controls

Validation controls ensure that user inputs meet specified criteria before submitting data to the server. These controls validate the input on both the client and server sides.

1. Definition

Validation controls are server controls used to check user inputs, ensuring they are correct and valid before processing further.

2. Properties and Methods of Validation Controls

All validation controls inherit from the base BaseValidator class and share common properties:

ControlToValidate: The ID of the control to validate.
ErrorMessage: The error message to display if validation fails.
IsValid: Returns True if validation is successful.
ValidationGroup: Groups validation controls together.

Methods:

Validate(): Triggers the validation process.
IsValid(): Returns whether the control passes the validation.

3. Types of Validation Controls

RequiredFieldValidator: Ensures that the associated input control is not empty.

Example:

<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="TextBox1" ErrorMessage="This field is required." />

CompareValidator: Compares the value of the input control with another value or control.

Example:

<asp:CompareValidator ID="CompareValidator1" runat="server" ControlToValidate="TextBox1" ControlToCompare="TextBox2" Operator="Equal" ErrorMessage="Values do not match." />

RangeValidator: Ensures that the input value is within a specified range.

Example:

<asp:RangeValidator ID="RangeValidator1" runat="server" ControlToValidate="TextBox1" MinimumValue="1" MaximumValue="10" Type="Integer" ErrorMessage="Value must be between 1 and 10." />

RegularExpressionValidator: Validates the input based on a regular expression pattern.

Example:

<asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server" ControlToValidate="TextBox1" ValidationExpression="\d{3}-\d{2}-\d{4}" ErrorMessage="Invalid format." />

CustomValidator: Allows custom server-side validation logic.

Example:

<asp:CustomValidator ID="CustomValidator1" runat="server" ControlToValidate="TextBox1" OnServerValidate="ValidateInput" ErrorMessage="Custom validation failed." />

Code-behind:

protected void ValidateInput(object source, ServerValidateEventArgs args) {
    args.IsValid = args.Value.Length > 5;
}

ValidationSummary: Displays a summary of validation errors in one place.

Example:
```
<asp:ValidationSummary ID="ValidationSummary1" runat="server" />
```

ASP.NET User Controls

User controls in ASP.NET are reusable page components, encapsulating the markup and code for a specific functionality, like a login form or a navigation bar.

1. Definition

A User Control is a reusable container of markup and server-side code, encapsulated into a .ascx file. User controls are typically used to modularize parts of a web application that are repeated across multiple pages.

2. Markup-Only User Control

A simple user control can contain only markup, which is placed in a .ascx file. For example, a header or footer section can be implemented as a markup-only user control.

Example:

<!-- Header.ascx -->
<div>
    <h1>Website Header</h1>
</div>

3. Custom Properties in User Controls

User controls can expose custom properties that allow pages to pass data to the user control.

Example:

<!-- UserControl.ascx -->
<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="UserControl.ascx.cs" Inherits="MyApp.UserControl" %>
<div>
    <h2><%= Title %></h2>
</div>

Code-behind:

public partial class UserControl : System.Web.UI.UserControl {
    public string Title { get; set; }
}

4. Handling Events in User Controls

User controls can also raise events that the hosting page can handle.

Example:

public event EventHandler ButtonClicked;
 
protected void Button_Click(object sender, EventArgs e) {
    ButtonClicked?.Invoke(this, EventArgs.Empty);
}

5. Loading User Controls Dynamically

User controls can be loaded dynamically at runtime using the LoadControl method.

Example:

protected void Page_Load(object sender, EventArgs e) {
    Control userControl = LoadControl("UserControl.ascx");
    PlaceHolder1.Controls.Add(userControl);
}

Unit - III Unit - I