1 <%@ Control Language="VB" ClassName="ClientCallbackControl"%>
 2 <%@ Implements Interface="System.Web.UI.ICallbackEventHandler"%>
 3 <script runat="server">
 4     ''This is the variable that holds the client callback
 5     ''results that will be returned to the client.
 6     Dim MyCallbackResult As String
 7 
 8     ''This is the server-side function that is called when the
 9     ''client callback results are returned to the browser.
10     Public Function GetCallbackResult() As String Implements System.Web.UI.ICallbackEventHandler.GetCallbackResult
11         Return MyCallbackResult
12     End Function
13 
14     ''This is the server-side function that is called when the
15     ''client callback is fired off.
16     Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent
17         MyCallbackResult = Now.ToString
18     End Sub
19 
20     Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
21         ''Get Client Side ID of this instance of the User Control
22         ''This will be used to Prefix all the JavaScript functions
23         ''this control uses so that you can have multiple instances
24         ''of this control on the same page.
25         Dim strJSCallbackPrefix As String = Me.ClientID
26 
27         ''Get the JavaScript that will callback to the server
28         Dim cm As ClientScriptManager = Page.ClientScript
29         Dim cbReference As String
30         cbReference = cm.GetCallbackEventReference(Me, _
31             "arg", _
32             strJSCallbackPrefix & "ReceiveServerData", _
33             "context")
34 
35         ''Declare the function that will be called to fire off a
36         ''client callback to the server.
37         Dim callbackScript As String = _
38             "function " & strJSCallbackPrefix & "CallServer(arg, context){" & cbReference & "; }"
39         cm.RegisterClientScriptBlock(Me.GetType(), strJSCallbackPrefix & "CallServer", callbackScript, True)
40 
41         ''Declare the function that will recieve the client callback
42         ''results from the server.
43         Dim strReceiveServerData As String = _
44             "function " & strJSCallbackPrefix & "ReceiveServerData(arg, context){context.innerHTML = arg;}"
45         cm.RegisterClientScriptBlock(Me.GetType, strJSCallbackPrefix & "ReceiveServerData", strReceiveServerData, True)
46 
47 
48         ''Set the JavaScript that is run when the button is clicked
49         ''This sends the context of lblMessage1 so that the
50         ''ReceiveServerData function can change its value to what is
51         ''returned from the server.
52         Button1.OnClientClick = _
53             strJSCallbackPrefix & "CallServer(1, document.getElementById('" & lblMessage1.ClientID & "')); " & _
54             "return false;"
55 
56 
57         ''Load lblMessage1 with it's value on initial load of the page.
58         RaiseCallbackEvent(1)
59         lblMessage1.Text = GetCallbackResult()
60     End Sub
61 </script>
62 <asp:Button ID="Button1" runat="server" Text="Get DateTime Stamp" />
63 &nbsp;&nbsp;
64 <asp:Label runat="server" ID="lblMessage1"></asp:Label>