using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;

namespace 图书管理系统
{
    /// <summary>
    /// Description of MainForm.
    /// </summary>
    public partial class MainForm : Form
    {
        public MainForm()
        {
            //
            // The InitializeComponent() call is required for Windows Forms designer support.
            //
            InitializeComponent();
            
            //
            // TODO: Add constructor code after the InitializeComponent() call.
            //
        }
        
        private bool checkChildFrmExist(string childFrmName)
        {
            foreach(Form childFrm in this.MdiChildren)
            {
                if(childFrm.Name == childFrmName) //用子窗体的Name进行判断，如果存在则将他激活
                {
                    if(childFrm.WindowState == FormWindowState.Minimized)
                        childFrm.WindowState = FormWindowState.Normal;
                    childFrm.Activate();
                    return true;
                }
            }
            return false;
        }

        private void 退出ToolStripMenuItem1Click(object sender, EventArgs e)
        {
            this.Close();
            return;
        }
        
        private void 关于ToolStripMenuItem1Click(object sender, EventArgs e)
        {
            about SubForm = new about();
            SubForm.ShowDialog();
        }
        
        private void 藏书管理ToolStripMenuItemClick(object sender, EventArgs e)
        {
            if (this.checkChildFrmExist("cangshu") == true)
            {
                return;
            }
            cangshu newFom = new cangshu();
            newFom.MdiParent = this;
            newFom.Show();
        }
    }
}

请教上述代码中，为什么一打开菜单中的子窗口就会提示newFom.MdiParent = this;这一句有问题呢。我用sharpdevelop的。

将MainForm 设置为this.IsMdiContainer=true