Ravikumar Codings: Raise event from user control to main page / Event delegation from user control to aspx page in ASP.NET,C#

"What is delegate?" we all have faced this question in one or more interview. :) and the most common answer is "Function pointer". Here I am showing a simple example of delegate. I have one user control and one aspx page. The user control contains one button. When user click on this button I will call a method on main page using delegate. Here is my user control,

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="WebUserControl.ascx.cs" Inherits="Dalegate_WebUserControl" %>
<asp:Button ID="btnTest" runat="server" Text="I am Inside User Control" OnClick="btnTest_Click" />
public partial class Dalegate_WebUserControl : System.Web.UI.UserControl
{
    // Delegate declaration
    public delegate void OnButtonClick(string strValue);

    // Event declaration
    public event OnButtonClick btnHandler;

   // Page load
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void btnTest_Click(object sender, EventArgs e)
    {
           // Check if event is null
           if (btnHandler != null)
               btnHandler(string.Empty);

           // Write some text to output
           Response.Write("User Control's Button Click <BR/>");
    }
}

WebUserControl.ascx.cs

          Above code first check whether btnHandler is not null and than raise the event by passing argument. You can pass any number of argument in event. You need to change public delegate void OnButtonClick(string strValue) and btnHandler(string.Empty) lines for changing number of arguments. Now take a look at aspx page,

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="Dalegate_Default" %>
<%@ Register Src="WebUserControl.ascx" TagName="WebUserControl" TagPrefix="uc1" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:Label ID="lblText" Text="I am On Main Page : "
                   runat="server"></asp:Label>
        <asp:DropDownList ID="ddlTemp" runat="server">
            <asp:ListItem>Chirag</asp:ListItem>
            <asp:ListItem>Dipak</asp:ListItem>
            <asp:ListItem>Shailesh</asp:ListItem>
        </asp:DropDownList>
        <br />
        <br />
        <uc1:WebUserControl ID="WebUserControl1"
           runat="server" />
    </div>
    </form>
</body>
</html>

Default.aspx

        Default.aspx has one drop down list and a user control as shown in above code. Lets look at cs file,

public partial class Dalegate_Default : System.Web.UI.Page
{
      protected void Page_Load(object sender, EventArgs e)
      {
             // Declare and Define Event of User Control. When User
             // Clicks on button (which is inside UserControl)
             // below event is raised as I have called raised that
             // event on Button Click
             WebUserControl1.btnHandler += new
             Dalegate_WebUserControl.OnButtonClick
             (WebUserControl1_btnHandler);

      }

      void WebUserControl1_btnHandler(string strValue)
      {
             Response.Write("Main Page Event<BR/>Selected
                  Value: " + ddlTemp.SelectedItem.Text + "<BR/>");
      }
}

Default.aspx.cs

Now when you run the application and clicks on button you can see that when user click on button the user control raise the click event and calls the WebUserControl1_btnHandler(string strValue) method on main page.

Source: chiragrdarji

Thursday, December 24, 2009

Raise event from user control to main page / Event delegation from user control to aspx page in ASP.NET,C#