Check if an object has focus

Question

How can I tell if a certain textbox has focus or not? I'm writing in C# in .NET.

Answer 1

Because performance can be a problem with generic solutions, the easiest thing I've come across so far is as follows:

1. Subscribe to the onFocus event of each control you care about.
2. In the onFocus handler, set a global variable (maybe "lastFocusElement") to the element that just received focus.
3. When you need to know that a certain control has focus, compare against the "lastFocusElement" variable.

Answer 2

You would have to use the javascript events OnFocus and OnBlur, and set a variable of some sort. Basically:

<script>
   var lastFocus=null;

    function DoesControlHaveFocus(var control){return control==lastFocus;}
</script>
<input type="text" onfocus="lastFocus=this" onblur="lastFocus=null"/>

FOR A version that would work in the code-behind, you would set a hidden field to the ID of the control in the OnFocus command, which you could then check.