private void kelolaUserToolStripMenuItem_Click(object sender, EventArgs e)
 {
     if (usermanager == null)
     {
         usermanager             = new usermanager();
         usermanager.MdiParent   = this.MdiParent;
         usermanager.FormClosed += new FormClosedEventHandler(Usermanager_FormClosed);
         usermanager.Show();
     }
     else
     {
         usermanager.Activate();
     }
 }
 private void Usermanager_FormClosed(object sender, FormClosedEventArgs e)
 {
     usermanager = null;
 }