.net Winform 控制子窗体在父窗体出现一次

        private void button1_Click(object sender, EventArgs e)
        {
            System.Windows.Forms.Form[] mdiForm = this.MdiChildren; //获取窗体的数组
            bool openFlage = false;//标识窗体是否打开（true:已打开了一个窗体）
            foreach (Form fr in mdiForm) //遍历所有MDIForm窗体
            {
                if (fr.Name == "SystemSet")//已打开一个窗体则激活并显示出来
                {
                    fr.Activate(); //激活窗体
                    openFlage = true;
                    break;
                }
            }
            if (!openFlage)//没有打开窗体则新建并显示出来
            {
                SystemSet SS = new SystemSet();
                SS.StartPosition = FormStartPosition.Manual;
                SS.Location = new Point(400, 100);
                SS.MdiParent = this;
                SS.Show();
            }
        }

===============lable 控件设置颜色========================

 label2.ForeColor = System.Drawing.Color.Blue;