c#，form打开新子窗口关闭旧其他子窗口

部分代码：

            //关闭其他窗口
            FormCollection childCollection = Application.OpenForms;
            for (int i = childCollection.Count; i-- > 0;)
            {
                if (childCollection[i] != this)
                    childCollection[i].Close();
                else
                    break;
            }

按键实现：

        private void t10chapwd_Click(object sender, EventArgs e)
        {
            //关闭其他窗口
            FormCollection childCollection = Application.OpenForms;
            for (int i = childCollection.Count; i-- > 0;)
            {
                if (childCollection[i] != this)
                    childCollection[i].Close();
                else
                    break;
            }

            this.IsMdiContainer = true;
            change_the_password chapwd = new change_the_password();
            chapwd.MdiParent = this;//this新窗口的父窗口
            chapwd.userno3 = userno1;//传参
            chapwd.Show();   
        }