zj-Exercise/C#/WindowsFormsDemo1/Form3.cs

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 WindowsFormsDemo1
{
    public partial class Form3 : Form
    {
        public Form3()
        {
            InitializeComponent();
        }

        private void Form3_Click(object sender, EventArgs e)
        {
            MessageBox.Show("你好");
        }

        private void Form3_FormClosing(object sender, FormClosingEventArgs e)
        {
            DialogResult dr = MessageBox.Show("是否关闭窗体","提示",MessageBoxButtons.YesNo,MessageBoxIcon.Warning);

            if (dr == DialogResult.Yes)
            {
                e.Cancel = false;   //false表示执行关闭操作
            }
            else { 
                e.Cancel = true;    //true表示不执行关闭窗体，即不关闭窗体
            }
        }

        private void Form3_Load(object sender, EventArgs e)
        {
            Form2 f2 = new Form2(); //实例化Form2窗体
            f2.Show();
            f2.MdiParent = this;    //this就表示当前的实例，也就是Form3

            Form1 f1 = new Form1();
            f1.Show();
            f1.MdiParent = this;

            Form4 f4 = new Form4();
            f4.Show();
            f4.MdiParent = this;
        }

        private void 水平平铺ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            LayoutMdi(MdiLayout.TileHorizontal);
        }

        private void 垂直平铺ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            LayoutMdi(MdiLayout.TileVertical);
        }
    }
}