Override standard close (X) button in a Windows Form

Question

How do I go about changing what happens when a user clicks the close (red X) button in a Windows Forms application (in C#)?

Answer 1

as Jon B said, but you'll also want to check for the ApplicationExitCall and TaskManagerClosing CloseReason:

protected override void OnFormClosing(FormClosingEventArgs e)
{
    if (  e.CloseReason == CloseReason.WindowsShutDown 
        ||e.CloseReason == CloseReason.ApplicationExitCall
        ||e.CloseReason == CloseReason.TaskManagerClosing) { 
       return; 
    }
    e.Cancel = true;
    //assuming you want the close-button to only hide the form, 
    //and are overriding the form's OnFormClosing method:
    this.Hide();
}