C#MDI中防止子窗体被多次实例化

第一种方式：

                if (gongChenJinDuFrm == null || gongChenJinDuFrm.IsDisposed)
                {
                    gongChenJinDuFrm = new GongChenJinDuFrm();
                }
                gongChenJinDuFrm.Text = "工程进度--" + DGJName;
                gongChenJinDuFrm.FillData(DGJID);
                gongChenJinDuFrm.MdiParent = this;
                gongChenJinDuFrm.WindowState = FormWindowState.Normal;
                gongChenJinDuFrm.MaximizeBox = false;
                gongChenJinDuFrm.StartPosition = FormStartPosition.CenterScreen;
                gongChenJinDuFrm.Show();

 

第二种方式：

 

        private static GongChenJinDuFrm gongChenJinDuFrm;
        private GongChenJinDuFrm GetGongChenJinDuFrm()
        {
            //先后次序不能错，前一个条件用来判断是否是第一次，后一个条件用来判断子窗体是否被关闭了
            if (gongChenJinDuFrm == null || gongChenJinDuFrm.IsDisposed)
            {    //第一次实例化也好，被关了也好，都重新实例化
                gongChenJinDuFrm = new GongChenJinDuFrm();
                gongChenJinDuFrm.MdiParent = this;
            }
            return gongChenJinDuFrm;
        }