ASP.NET Tutorial/ASP.net Controls/CheckBox

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asp: CheckBox changed event (C#)

   <source lang="csharp">

File: Default.aspx <%@ Page language="c#" Inherits="EventTracker" CodeFile="Default.aspx.cs" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"

"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

<html xmlns="http://www.w3.org/1999/xhtml"> <head id="Head1" runat="server">

 <title>Event Tracker</title>

</head> <body>

 <form id="Form1" runat="server">

Controls being monitored for change events:

     <asp:TextBox ID="txt" 
                  runat="server" 
                  AutoPostBack="true"
                  OnTextChanged="CtrlChanged" />
     

<asp:CheckBox ID="chk" runat="server" AutoPostBack="true" OnCheckedChanged="CtrlChanged"/>

<asp:RadioButton ID="opt1" runat="server" GroupName="Sample" AutoPostBack="true" OnCheckedChanged="CtrlChanged"/> <asp:RadioButton ID="opt2" runat="server" GroupName="Sample" AutoPostBack="true" OnCheckedChanged="CtrlChanged"/>


List of events:

     <asp:ListBox ID="lstEvents" runat="server" Width="355px"
      Height="305px" />
 </form>

</body> </html>

File: Default.aspx.cs using System; using System.Collections; using System.ruponentModel; using System.Data; using System.Drawing; using System.Web; using System.Web.SessionState; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.HtmlControls;

public partial class EventTracker : System.Web.UI.Page {

 protected void Page_Load(object sender, System.EventArgs e)
 {
    Log("<< Page_Load >>");
 }
 private void Log(string entry)
 {
   lstEvents.Items.Add(entry);
   lstEvents.SelectedIndex = lstEvents.Items.Count - 1;
 }
 protected void Page_PreRender(object sender, System.EventArgs e)
 {
   Log("Page_PreRender");
 }
 protected void CtrlChanged(Object sender, EventArgs e)
 {
   string ctrlName = ((Control)sender).ID;
   Log(ctrlName + " Changed");
 }

}</source>


Get selected CheckBox

   <source lang="csharp">

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="CheckBox" %> <html xmlns="http://www.w3.org/1999/xhtml" > <head runat="server">

   <title>Untitled Page</title>

</head> <body>

   <form id="form1" runat="server">
       What are your favorite ice cream flavors?

<asp:CheckBox ID="A" runat="server" Text="A" />

<asp:CheckBox ID="B" runat="server" Text="B" />

<asp:CheckBox ID="C" runat="server" Text="C" />

<asp:Button ID="btnSubmit" runat="server" Text="Click Me" />

<asp:Label ID="results" runat="server"></asp:Label>
   </form>

</body> </html>

File: Default.aspx.vb Partial Class CheckBox

   Inherits System.Web.UI.Page
   Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSubmit.Click
       results.Text = ""
       If A.Checked Then
           results.Text &= "A."
       End If
       If B.Checked Then
           results.Text &= "B."
       End If
       If C.Checked Then
           results.Text &= "C."
       End If
   End Sub

End Class</source>


Import properties, events and methods of CheckBox control

   <source lang="csharp">

AccessKey: specify a key that navigates to the TextBox control. AutoPostBack: post the form containing the CheckBox back to the server automatically when the CheckBox is checked or unchecked. Checked: get or set whether the CheckBox is checked. Enabled: disable the TextBox. TabIndex: specify the tab order of the check box. Text: provide a label for the check box. TextAlign: align the label for the check box. Possible values are Left and Right. Focus: set the initial form focus to the check box. CheckedChanged: Raised on the server when the check box is checked or unchecked. <%@ Page Language="C#" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <script runat="server">

   protected void btnSubmit_Click(object sender, EventArgs e)
   {
       lblResult.Text = chkNewsletter.Checked.ToString();
   }

</script> <html xmlns="http://www.w3.org/1999/xhtml" > <head id="Head1" runat="server">

   <title>Show CheckBox</title>

</head> <body>

   <form id="form1" runat="server">
   <asp:CheckBox
       id="chkNewsletter"
       Text="Receive Newsletter?"
       Runat="server" />
   
<asp:Button id="btnSubmit" Text="Submit" OnClick="btnSubmit_Click" Runat="server" />

   <asp:Label
       id="lblResult"
       Runat="server" />
   </form>

</body> </html></source>


use the AutoPostBack property to post the form to the server automatically when the check box is checked or unchecked.

   <source lang="csharp">

<%@ Page Language="C#" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <script runat="server">

   protected void chkNewsletter_CheckedChanged(object sender, EventArgs e)
   {
       lblResult.Text = chkNewsletter.Checked.ToString();
   }

</script> <html xmlns="http://www.w3.org/1999/xhtml" > <head id="Head1" runat="server">

   <title>CheckBox AutoPostBack</title>

</head> <body>

   <form id="form1" runat="server">
   <asp:CheckBox
       id="chkNewsletter"
       Text="Receive Newsletter?"
       AutoPostBack="true"
       OnCheckedChanged="chkNewsletter_CheckedChanged"
       Runat="server" />

   <asp:Label
       id="lblResult"
       Runat="server" />
   </form>

</body> </html></source>