Question

I am trying to close my application when closing the menu form.
This is my code:

private void frmMenu_FormClosing(object sender, FormClosingEventArgs e)
{
    var result = MessageBox.Show("Do you want to close this application",
        "Alert", MessageBoxButtons.YesNo, MessageBoxIcon.Warning);
    if (result == DialogResult.Yes)
    {
        //this.Close();
        Application.Exit();
        //e.Cancel = false;
    }
    else
    {
        e.Cancel = true;
    }
}

When closing this message appears twice.

Answer 1

You can override the OnFormClosing method:

protected override void OnFormClosing(FormClosingEventArgs e) {
        base.OnFormClosing(e);
        if (!e.Cancel) {
            if (MessageBox.Show("Do you want to close this application?", "Close Application", MessageBoxButtons.YesNo) != DialogResult.Yes) {
                e.Cancel = true;
            }
        }
    }

Or following Hans Passant‘s advice in the comments on using a bool (e.g. IsDataValid) in your class:

private void frmMenu_FormClosing(object sender, FormClosingEventArgs e)
{ 
   if (!IsDataValid)
   {
       if(DialogResult.Yes == MessageBox.Show(Do you want to close this application?",
        "Alert", MessageBoxButtons.YesNo, MessageBoxIcon.Question))
           this.Dispose(); //or Application.Exit();
       else
            e.Cancel = true;
   }
   else
       this.Dispose(); //or Application.Exit();
}