private void button4_Click(object sender, EventArgs e) { Form f = Application.OpenForms["Fenpei"]; //查找是否打开过Form1窗体 if (f == null) //没打开过 { Fenpei fenpei = new Fenpei(); fenpei.MdiParent = this.MdiParent; fenpei.Show(); } else { f.Focus(); //打开过就让其获得焦点 } }