窗体容器

public void showform(Form f)
        {
            int count = 0;//用来记录是否有打开的窗体
            foreach(Form ff in this.MdiChildren)//遍历容器中已经打开的窗体
            {
                if (f.Name == ff.Name)//如果重名，说明已经存在
                {
                    ff.Focus();//将已经打开的窗体聚焦
                    count++;//计数
                }
            }
            if (count == 0)//如果没有打开的同名窗体，第一次点击窗体时，已经打开的子窗体为空，count=0
            {
                f.MdiParent = this;//在容器中
                f.Show();//打开
            }
        }
        private void 窗体一ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Form2 f = new Form2();
            showform(f);
        }

        private void 窗体二ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Form3 f = new Form3();
            showform(f);
        }

        private void menuStrip1_ItemClicked(object sender, ToolStripItemClickedEventArgs e)
        {
            //首先在属性中设置ismdicontainer为true,是否为container容器
        }