Page.FindControl() Returning Null Issues and Solutions Within Another Control

Alright, I’m going to have a lot of blog posts over the next few days going over my wonderful expereinces learning how to create advanced server controls, and just how hard it is to find good information on the subject. But the problem I ran into today was having Page.FindControl() not work as expected.

Problem

Page.FindControl() can be misleading. A developer without understanding the situation could assume FindControl() will return a control found within that page. This is completely wrong. The reason this does not work is because Page does not have its own FindControl() function. It actually inherits this from Control, because Page inherits control. So FindControl() is really more like a FindChildrenControls(), and it is not recursive.

Example

I have some code that does a Page.FindControl() for a GridView. However, later I move the GridView into an UpdatePanel to add ajax enabled stuff. All of a sudden my Page.FindControl() doesn’t work. The reason? Because my GridView is no longer a direct child of the Page and it is now a child of the UpdatePanel. So instead of being Page -> GridView it is Page -> UpdatePanel -> GridView.

Solution

I found a blog post for a recursive post. Here is the code:

private Control FindControlRecursive(Control root, string id)
{
if (root.ID == id)
{
return root;
}

foreach (Control c in root.Controls)
{
Control t = FindControlRecursive(c, id);
if (t != null)
{
return t;
}
}

return null;
}