LINQ Casting issue

Question

I have a winform with two checkboxes and a button. On the CheckedChanged event of both checkboxes i had given the following code.

//Enable the button if any of the checkbox is checked
var ChkBoxes = from CheckBox ctrl in this.Controls 
               where ctrl is CheckBox select ctrl;
button1.Enabled = ChkBoxes.Any(c => ((CheckBox)c).Checked);

but when checking either of the checkboxes I am getting an error "Unable to cast object of type 'System.Windows.Forms.Button' to type 'System.Windows.Forms.CheckBox'." the error comes up while executing the second line of code.

Later I updated the code to the following, which works fine. The only change I made is modified ctrl type from CheckBox to Control.

var ChkBoxes = from Control ctrl in this.Controls 
               where ctrl is CheckBox select ctrl;
button1.Enabled = ChkBoxes.Any(c => ((CheckBox)c).Checked);

My question is, in both cases I am returning controls only of type checkbox, then how come the cast error comes up. Can anyone explain me how this works?

Answer 1

Instead of using:

var ChkBoxes = from CheckBox ctrl in this.Controls where ctrl is CheckBox select ctrl;

Try using Enumerable.OfType<T> to do your filtering:

var chkBoxes = this.Controls.OfType<CheckBox>();
button1.Enabled = chkBoxes.Any(c => c.Checked); // No cast required now