在项目中另外添加一个windows窗体Form2
右键Form1更改属性，把IsMdiContainer设置为true
双击Form1设计窗体进入编辑模式，修改代码如下
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace WindowsFormsHelloWorld
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
Form2 frm2 = new Form2();
frm2.MdiParent = this;
frm2.Show();
}
}
}
F5运行结果