Windows Forms' CheckBox CheckedChanged vs. CheckStateChanged

Question

Windows Forms' 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

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.

Answer 2

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);  }