ASP.NET Tutorial/Page Lifecycle/GetCallbackEventReference
Server side call back (C#)
<source lang="csharp">
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="RandomNumber" %> <!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 id="Head1" runat="server">
<title>Callback Page</title>
<script type="text/javascript">
function GetNumber(){
UseCallback();
}
function GetRandomNumberFromServer(TextBox1, context){
document.forms[0].TextBox1.value = TextBox1;
}
</script>
</head> <body>
<form id="form1" runat="server">
<input id="Button1"
type="button"
value="Get Random Number"
onclick="GetNumber()" />
<asp:TextBox ID="TextBox1" Runat="server"></asp:TextBox>
</form>
</body> </html> File: Default.aspx.cs using System; using System.Data; using System.Configuration; using System.Collections; using System.Web; using System.Web.Security; using System.Web.UI; using System.Web.UI.WebControls; using System.Web.UI.WebControls.WebParts; using System.Web.UI.HtmlControls; public partial class RandomNumber : System.Web.UI.Page, System.Web.UI.ICallbackEventHandler {
private string _callbackResult = null;
protected void Page_Load(object sender, EventArgs e)
{
string cbReference = Page.ClientScript.GetCallbackEventReference(this,
"arg", "GetRandomNumberFromServer", "context");
string cbScript = "function UseCallback(arg, context)" +
"{" + cbReference + ";" + "}";
Page.ClientScript.RegisterClientScriptBlock(this.GetType(),
"UseCallback", cbScript, true);
}
public void RaiseCallbackEvent(string eventArg)
{
Random rnd = new Random();
_callbackResult = rnd.Next().ToString();
}
public string GetCallbackResult()
{
return _callbackResult;
}
}</source>
Server side call back (VB)
<source lang="csharp">
<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="RandomNumber" %> <!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 id="Head1" runat="server">
<title>Callback Page</title>
<script type="text/javascript">
function GetNumber(){
UseCallback();
}
function GetRandomNumberFromServer(TextBox1, context){
document.forms[0].TextBox1.value = TextBox1;
}
</script>
</head> <body>
<form id="form1" runat="server">
<input id="Button1"
type="button"
value="Get Random Number"
onclick="GetNumber()" />
<asp:TextBox ID="TextBox1" Runat="server"></asp:TextBox>
</form>
</body> </html> File: Default.aspx.vb
Partial Class RandomNumber
Inherits System.Web.UI.Page
Implements System.Web.UI.ICallbackEventHandler
Dim _callbackResult As String = Nothing
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) _
Handles Me.Load
Dim cbReference As String = Page.ClientScript.GetCallbackEventReference(Me, "arg", "GetRandomNumberFromServer", "context")
Dim cbScript As String = "function UseCallback(arg, context)" & _
"{" & cbReference & ";" & "}"
Page.ClientScript.RegisterClientScriptBlock(Me.GetType(), _
"UseCallback", cbScript, True)
End Sub
Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent
_callbackResult = Rnd().ToString()
End Sub
Public Function GetCallbackResult() As String Implements System.Web.UI.ICallbackEventHandler.GetCallbackResult
Return _callbackResult
End Function
End Class</source>
