Asp.NET custom server control event handler not firing on second postback

Question

I'm developing a custom server control in Asp.NET (.NET 3.5) which inherits the CompositeControl class. Inside my control I'm overriding the CreateChildControls() method to generate a mixture of html and Asp.NET server controls. Some of the Asp.NET controls which are added are LinkButton s (which each have their Command event handler set to a method within my control). What I'm finding is that the first time one of these LinkButtons is clicked a postback is triggered and the event handler method is correctly fired. Inside this event handler method CreateChildControls() is explicitly called to regenerate the control in response to the postback. What I then find is that subsequent clicks of the LinkButton s postbacks fail to raise the event handler method.

I assume that the way I'm handling the regeneration of the control on postback must be at fault, but I can't figure out what to do - I am aware of the fact that on that first postback CreateChildControls() is called twice which probably isn't ideal but since CreateChildControls is called before any events are raised, I don't see a way around this.

A simplified version of my control class is shown below:

public class SearchResults : CompositeControl
{
    private int PageIndex = 0;

    protected override void CreateChildControls()
    {
            //do stuff here e.g.
            LinkButton prevLink = new LinkButton();
            prevLink.Text = "< Prev";
            prevLink.CommandArgument = (PageIndex - 1).ToString();
            prevLink.Command += new CommandEventHandler(PagerLinkCommand);
            this.Controls.Add(prevLink);
    }

    protected void PagerLinkCommand(object sender, CommandEventArgs e)
    {
        PageIndex = int.Parse(e.CommandArgument.ToString());
        CreateChildControls();
    }
}

EDIT The problem here was caused by the fact that the control is used in a Sitecore site and I had forgotten to register the control type in the web.config file with a <typesThatShouldNotBeExpanded> entry. This entry is used to prevent server controls from having their events messed up by Sitecore - this can cause similar problems for standard server controls such as ListView, GridView and Repeater etc. My web.config was modified as shown below:

  <typesThatShouldNotBeExpanded>
    <type>System.Web.UI.WebControls.Repeater</type>
    <type>System.Web.UI.WebControls.DataList</type>
    <type>System.Web.UI.WebControls.GridView</type>
    <type>MyNamespace.MyCustomControl</type> <!-- This is the bit I added -->
  </typesThatShouldNotBeExpanded>

Answer 1

In my experience this sort of problem is usually due to not assigning an ID to dynamically generated controls.

LinkButton prevLink = new LinkButton();
prevLink.ID = "prevLink";

Answer 2

Apologies... this is not a complete answer, but a debugging suggestion that is too long for a comment:

In your browser save an HTML copy of your page for initial load, postback load, and second postback. Then compare the files using your favorite comparison tool. Eliminate obvious differences like search results, etc. This can help you pinpoint any issues with control IDs, missing controls, etc.

The two absolute keys to successful dynamically created controls are
1) Creating them at the correct time during the page lifecycle
2) Re-creating the EXACT SAME control hierarchy (including IDs) on postback

Answer 3

To get the proper control tree override the Controls property and call the EnsureChildControls, and also call the EnsureChildControls and not the CreateChildControls inside the PagerLinkCommand.

    /// <summary>
    /// Gets controls.
    /// </summary>
    public override ControlCollection Controls
    {
        get
        {
            EnsureChildControls();
            return base.Controls;
        }
    }

    /// <summary>
    /// Create child controls.
    /// </summary>
    protected override void CreateChildControls()
    {
        this.Controls.Clear();
        //do stuff here e.g.
        LinkButton prevLink = new LinkButton();
        prevLink.Text = "< Prev";
        prevLink.CommandArgument = (PageIndex - 1).ToString();
        prevLink.Command += new CommandEventHandler(PagerLinkCommand);
        this.Controls.Add(prevLink);
    }

    protected void PagerLinkCommand(object sender, CommandEventArgs e)
    {
      PageIndex = int.Parse(e.CommandArgument.ToString());
      EnsureChildControls();
    }        

Answer 4

The reason for this behaviour was not down to the server control itself, but was Sitecore-related. In order for Sitecore to not interfere with server control postbacks, it is necessary to add an entry under the typesThatShouldNotBeExpanded section in the web.config file as shown below.

<typesThatShouldNotBeExpanded>
  <type>System.Web.UI.WebControls.Repeater</type>
  <type>System.Web.UI.WebControls.DataList</type>
  <type>System.Web.UI.WebControls.GridView</type>
  <type>MyNamespace.MyCustomControl</type> <!-- This is the bit I added -->
</typesThatShouldNotBeExpanded>