03 Open the other frm by button

private void Form1_formclosing (object sender, FormClosingEventArgs e)
{
DialogResult re = MessageBox.Show ("OK to leave", "inquiry", messageboxbuttons.yesno,messageboxicon.question);
if (re==dialogresult.no)
{
E.cancel = true;
}
}

private void Button1_Click (object sender, EventArgs e)
{
This. Close (); Click on the button to implement the close window
}

private void Button2_Click (object sender, EventArgs e)
{
Form2 frm = new Form2 ();
frm. ShowDialog (); ShowDialog modal form if you want to close the main form, you must first close the modal form
frm. Show ();//show can click the main window again to open countless windows without forcing a new window
}

03 Open the other frm by button