WinForm连续点击按钮只打开一次窗体

//设置只打开一次公用方法
public static int cxypx(Form frmMdiFather, string strMdiChild)
        {
            int bReturn = -1;
            for (int i = 0; i < frmMdiFather.MdiChildren.Length; i++)
            {
                if (frmMdiFather.MdiChildren[i].Name == strMdiChild)
                {
                    frmMdiFather.MdiChildren[i].BringToFront();
                    bReturn = i;
                    break;
                }
            }
            return bReturn;
        }

//然后再在你的按钮单击事件中加入以下代码：
private void 添加账单ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            int index = cxypx(this, "ZD");//记住，这里的ZD是子窗体的名字
            if (index == -1)
            {
                ZD tjzb = new ZD();//tjzb是子窗体的一个实例，就这连个地方改改就可以了
                tjzb.MdiParent = this;
                tjzb.Show();
            }
            else
            {
                this.MdiChildren[index].Show();
            }
        }