WinForm's CheckBox CheckedChanged vs. CheckStateChanged

Question

WinForm CheckBox control implements both CheckedChanged and CheckStateChanged events. As far as I can tell both fire when the checked status of the checkbox is changed. CheckedChanged precedes CheckStateChanged, but other than that I see no difference. Am I missing something? Should one be preferred over another?

Answer 1

My guess would be that it has to do with tri-state checkboxes. This is the guts of the CheckState setter:

 if (this.checkState != value)
 {
   bool flag = this.Checked;
   this.checkState = value;
   if (base.IsHandleCreated)
   {
     base.SendMessage(0xf1, (int) this.checkState, 0);
   }
   if (flag != this.Checked)
   {
     this.OnCheckedChanged(EventArgs.Empty);
   }
   this.OnCheckStateChanged(EventArgs.Empty);
 }

Answer 2

CheckState (and thus CheckStateChanged) allow for using a checkbox that can have three values: it can be checked, unchecked or 'indeterminate' - i.e. it has ThreeState set to true.

If you're not using ThreeState, then CheckedChanged is all you need.