Preventing a dialog from closing in the button's click event handler

Question

I have a dialog that I show with .ShowDialog(). It has an OK button and a Cancel button; the OK button also has an event handler.

I want to

Answer 1

Don't use the FormClosing event for this, you'll want to allow the user to dismiss the dialog with either Cancel or clicking the X. Simply implement the OK button's Click event handler and don't close until you are happy:

private void btnOk_Click(object sender, EventArgs e) {
  if (ValidateControls())
    this.DialogResult = DialogResult.OK;
}

Where "ValidateControls" is your validation logic. Return false if there's something wrong.