Question

I’m really new to the WebControl / CompositeControl world, and I have a small test class I am playing with. It’s just a LinkButton that updates when clicked. Things work great when I leave it out of UpdatePanel. But when I try to run it inside I still get a full page POST response. How can I make this class work inside a UpdatePanel?

Here’s the class:

public class Test2 : CompositeControl 
{
    private static readonly object testButtonEvent = new object();

    public event EventHandler OnTestClick
    {
        add { Events.AddHandler(testButtonEvent, value); }
        remove { Events.RemoveHandler(testButtonEvent, value); }
    }

    private LinkButton testLinkButton;

    public virtual string testLinkButtonText
    {
        get
        {
            object o = ViewState["testLinkButtonText"];
            return (o == null) ? String.Empty : (string)o;
        }
        set
        {
            if (value == null)
                ViewState.Remove("testLinkButtonText");
            else
                ViewState["testLinkButtonText"] = value;
        }
    }   

    protected override void OnInit(EventArgs e)
    {
        /* This stuff makes it ajax friendly but stops the text rendering
        EnsureChildControls();

        ScriptManager ScMan = ScriptManager.GetCurrent(Page);
        if (ScMan != null)
        {
            ScMan.RegisterAsyncPostBackControl(testLinkButton);
        }            */

        base.OnInit(e);
    }

    protected override void CreateChildControls()
    {
        Controls.Clear();

        testLinkButton = new LinkButton();
        testLinkButton.Command += new CommandEventHandler(testClick);
        testLinkButtonText = "Test ViewState Text";

        Controls.Add(testLinkButton);
    }

    void testClick(object sender, CommandEventArgs e)
    {
        testLinkButtonText = "Updated Text On " + DateTime.Now.ToLongTimeString();
    }

    protected override void Render(HtmlTextWriter writer)
    {
        RenderContents(writer);
    }

    protected override void RenderContents(HtmlTextWriter writer)
    {
        EnsureChildControls();

        testLinkButton.Text = testLinkButtonText;
        testLinkButton.RenderControl(writer);            
    }

}

The code in OnInit() causes the control to post correctly, but I don’t get the updated text for the LinkButton. It is still firing off the event – when I debug I can see it being called. What’s the proper way to set this control up for use in a UpdatePanel?

Usage, just in case:

<asp:UpdatePanel runat="server" UpdateMode="Conditional">
    <ContentTemplate>
        <cc:Test2 ID="jqTest02" runat="server" />
    </ContentTemplate>
</asp:UpdatePanel>

Answer 1

You have to give the button an ID property…this is used in the client-side javascript that drives the UpdatePanel. More specifically, it’s listed in the list of controls to intercept and do async postbacks for.

testLinkButton.ID = "btn";