how to focus mdi parent form control when i close child form

to put this code in mdiparent form: void child_FormClosed(object sender, FormClosedEventArgs e) { if (this.MdiChildren.Length == 1) { this.BeginInvoke(new MethodInvoker(() => btnitemcreate.Focus())); } } private void btnitemcreate_Click(object sender, EventArgs e) { TEST objStudentDetails = new TEST(); objStudentDetails.MdiParent = this; objStudentDetails.Show(); objStudentDetails.FormClosed += new FormClosedEventHandler(child_FormClosed);}