Specified cast is not valid in asp.net/c# foreach loop

Bashing my head against this and seeking ideas.  I have an ASP.NET page which contains a bunch of checkboxes in a panel.  They are standalone checkboxes, not a checkboxlist and need to be that way so that they can be formatted on the page.

Upon submitting the form, I need to loop through each checkbox and see if it is checked, and take action.  Here's my code:

private void butSubmit_Click(object sender, System.EventArgs e)
{
  foreach (CheckBox ck in pnlCheckboxes.Controls)
  {

      if(ck.Checked == true)
      {
          ... do stuff

The code compiles and at runtime errors at the foreach statement with the error "Specified cast is not valid"

Any ideas?  I've used similar code to loop through the checkboxes in a checkboxlist, but need to do it with standalone controls.

Aaron

Perhaps there is some non-CheckBox control within pnlCheckboxes?  Can you step through the code and manually validate that each item in pnlCheckboxes.Controls is a CheckBox?  If not, the foreach will throw the error.

You could always just change the foreach variable to something more generic and use as to check the type:

foreach (object o in pnlCheckboxes.Controls)
{
   CheckBox chk = o as CheckBox;

   if (chk == null)
      continue;

   if (chk.Checked)
   {
      // your code
   }
}

Does using "as" not throw a cast exception if "o" is of the wrong type?  Neat, I didn't know that... I always did soemthing like

if (o is CheckBox)
{
   CheckBox chk = (CheckBox)chk;
   // ...
}

Thanks for the replies, that info helped... by checking the object type I only attempt to deal with CheckBoxes.

Wow, that was quick. I learn something new everyday!

This is one thing that really bugs me about C#. In VB6 I could do this:
Dim blah as SomeObject
For Each blah in SomeCollection
 blah.foo
Next blah
And it would iterate through all the SomeObjects in SomeCollection, and ignore everything else.
In C# it errors out.

as tries to cast the object to the specified type and on failure it returns null.

Extra handy.

Although with just plane "as", you still have to check for null.  I'd like so see something like

with (CheckBox chk = o as CheckBox)
{
   // body
}

where body is only executed if o is a CheckBox.  This could be expanded out to...

with (CheckBox chk = o as CheckBox)
{
   // body
}
else with (ToolBarButton tbb = o as ToolBarButton)
{
   // other body
}
else
{
   // another body
}

That would be useful to me, and quite compact.  But I think "with" is a VB keyword, isn't it?

This works!!!:

foreach (ListItem checkbox in myCheckBoxList.Items)
{
   checkbox.Selected = true;
}


More info can be found here:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vbcon/html/vbtsksettingselectioninlistbox.asp



Hope that helps.


(Sorry, this is not specific to your problem)