一、创建父窗体Form1

VS中选择C#的Windows窗体应用创建父窗体Form1，默认生成Program.cs、Form1.cs、Form1.Designer.cs三个C#文件，右键Form1.cs有两种显示模式，一种为查看代码Form1.cs，一种为查看设计器Form1.cs[设计]。查看设计器Form1.cs[设计]，右键属性，把属性IsMdiContainer的值修改为True。

二、创建子窗体Form2，并在Form1中显示

1、首先在Form1.cs的Form1_Load（）中增加代码段

在资源管理器中，右键项目（比如App1），添加窗体（Windows窗体），生成窗体Form2。

以此类推可以生成窗体Form3、Form4。

在父窗体Form1中实现加载Form1时自动加载子窗体Form2，需要在Form1.cs的Form1_Load（）中增加代码段：

Form2 frm2 = new()
{
    MdiParent = this
};
frm2.Show();

以此类推，可以自动加载子窗体Form3、Form4。

//在主窗体中创建子窗体，并在主窗体打开时自动加载子窗体
namespace App1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            Form2 frm2 = new()//自动加载Form2
            {
                MdiParent = this
            };
            frm2.Show();

            Form3 frm3 = new()//自动加载Form3
            {
                MdiParent = this
            };
            frm3.Show();

            Form4 frm4 = new()//自动加载Form4
            {
                MdiParent = this
            };
            frm4.Show();
        }
    }
}

2、其次还要修改Form1.Designer.cs的窗体设计生成器

（1）修改前

        #region Windows Form Designer generated code

        /// <summary>
        ///  Required method for Designer support - do not modify
        ///  the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            SuspendLayout();
            // 
            // Form1
            // 
            AutoScaleDimensions = new SizeF(7F, 17F);
            AutoScaleMode = AutoScaleMode.Font;
            ClientSize = new Size(421, 393);
            IsMdiContainer = true;
            Name = "Form1";
            Text = "Form1";
            ResumeLayout(false);
        }

        #endregion
    }
}

（2）修改后

        #region Windows Form Designer generated code

        /// <summary>
        ///  Required method for Designer support - do not modify
        ///  the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            SuspendLayout();
            // 
            // Form1
            // 
            AutoScaleDimensions = new SizeF(7F, 17F);
            AutoScaleMode = AutoScaleMode.Font;
            ClientSize = new Size(421, 393);
            IsMdiContainer = true;
            Name = "Form1";
            Text = "Form1";
            Load += Form1_Load;        //在父窗体中显示子窗体，增加
            ResumeLayout(false);
        }
        #endregion

（3）生成结果：在父窗体中打开所有子窗体

三、排列子窗体

如果一个MDI窗体中有多个子窗体同时打开，假如不对其排列顺序进行调整，那么界面会非常混乱，而且不容易浏览。这时候，可以通过使用带有MdiLayout枚举的LayoutMdi()方法来排列多文档界面父窗体中的子窗体。

语法如下：
public void LayoutMdi(MdiLayout value)
value：是MdiLayout枚举值之一，用来定义MDI子窗体的布局。
MdiLayout枚举用于指定MDI父窗体中子窗体的布局，其格式：
public enum MdiLayout
MdiLayout的枚举成员如下表：

枚举成员	说明
Cascade	所有子窗体均层叠在MDI父窗体工作区内
TileHorizontal	所有子窗体均水平平铺在MDI父窗体工作区内
TileVertical	所有子窗体均垂直平铺在MDI父窗体工作区内

在上述的实例中继续操作，在Form1窗体中，添加一个MenuStip控件用作该父窗体的菜单项。通过MenuStrip控件建立3个菜单项，分别为“水平平铺”、“垂直平铺”、“层叠排列”。运行程序时通过Form1_Load加载所有子窗体，通过“水平平铺”、“垂直平铺”、“层叠排列”对所有子窗体进行排列。

1、先在Form1窗体中，添加一个MenuStip控件

打开Form1.cs[设计]→视图→工具箱（或左侧边框的工具箱）→菜单和工具栏→MenuStip→用鼠标拖拽图标到Form1窗体上边框放下→依次根据提示编辑输入菜单项“水平平铺”、“垂直平铺”、“层叠排列”。（为了观察窗体设计生成器内容的变化，鼠标不要点击控件）

2、窗体设计生成器内容的自动变化

        #region Windows Form Designer generated code

        /// <summary>
        ///  Required method for Designer support - do not modify
        ///  the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            menuStrip1 = new MenuStrip();
            水平平铺ToolStripMenuItem = new ToolStripMenuItem();
            垂直平铺ToolStripMenuItem = new ToolStripMenuItem();
            层叠排列ToolStripMenuItem = new ToolStripMenuItem();
            menuStrip1.SuspendLayout();
            SuspendLayout();
            // 
            // menuStrip1
            // 
            menuStrip1.Items.AddRange(new ToolStripItem[] { 水平平铺ToolStripMenuItem, 垂直平铺ToolStripMenuItem, 层叠排列ToolStripMenuItem });
            menuStrip1.Location = new Point(0, 0);
            menuStrip1.Name = "menuStrip1";
            menuStrip1.Size = new Size(484, 25);
            menuStrip1.TabIndex = 1;
            menuStrip1.Text = "menuStrip1";
            // 
            // 水平平铺ToolStripMenuItem
            // 
            水平平铺ToolStripMenuItem.Name = "水平平铺ToolStripMenuItem";
            水平平铺ToolStripMenuItem.Size = new Size(68, 21);
            水平平铺ToolStripMenuItem.Text = "水平平铺";
            // 
            // 垂直平铺ToolStripMenuItem
            // 
            垂直平铺ToolStripMenuItem.Name = "垂直平铺ToolStripMenuItem";
            垂直平铺ToolStripMenuItem.Size = new Size(68, 21);
            垂直平铺ToolStripMenuItem.Text = "垂直平铺";
            // 
            // 层叠排列ToolStripMenuItem
            // 
            层叠排列ToolStripMenuItem.Name = "层叠排列ToolStripMenuItem";
            层叠排列ToolStripMenuItem.Size = new Size(68, 21);
            层叠排列ToolStripMenuItem.Text = "层叠排列";
            // 
            // Form1
            // 
            AutoScaleDimensions = new SizeF(7F, 17F);
            AutoScaleMode = AutoScaleMode.Font;
            ClientSize = new Size(484, 461);
            Controls.Add(menuStrip1);
            IsMdiContainer = true;
            MainMenuStrip = menuStrip1;
            Name = "Form1";
            SizeGripStyle = SizeGripStyle.Hide;
            Text = "Form1";
            Load += Form1_Load;
            menuStrip1.ResumeLayout(false);
            menuStrip1.PerformLayout();
            ResumeLayout(false);
            PerformLayout();
        }

        #endregion

        private MenuStrip menuStrip1;
        private ToolStripMenuItem 水平平铺ToolStripMenuItem;
        private ToolStripMenuItem 垂直平铺ToolStripMenuItem;
        private ToolStripMenuItem 层叠排列ToolStripMenuItem;
    }
}

3、激活控件菜单项的Click事件

（1）鼠标点击控件菜单项“水平平铺”

观察窗体设计生成器自动新增内容和Form1.cs自动新增的内容。

//Form1.cs
namespace App3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        //在Form1_Load()中显示所有子窗体
        private void Form1_Load(object sender, EventArgs e)
        {

            Form2 frm2 = new()//自动加载Form2
            {
                MdiParent = this
            };
            frm2.Show();
            Form3 frm3 = new()//自动加载Form3
            {
                MdiParent = this
            };
            frm3.Show();
            Form4 frm4 = new()//自动加载Form4
            {
                MdiParent = this
            };
            frm4.Show();
        }
        //激活菜单项“水平平铺”的Click事件
        private void 水平平铺ToolStripMenuItem_Click(object sender, EventArgs e)
        {

        }
    }
}

//Form1.Designer.cs
namespace App3
{
    partial class Form1
    {
        /// <summary>
        ///  Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        ///  Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        ///  Required method for Designer support - do not modify
        ///  the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            menuStrip1 = new MenuStrip();
            水平平铺ToolStripMenuItem = new ToolStripMenuItem();
            垂直平铺ToolStripMenuItem = new ToolStripMenuItem();
            层叠排列ToolStripMenuItem = new ToolStripMenuItem();
            menuStrip1.SuspendLayout();
            SuspendLayout();
            // 
            // menuStrip1
            // 
            menuStrip1.Items.AddRange(new ToolStripItem[] { 水平平铺ToolStripMenuItem, 垂直平铺ToolStripMenuItem, 层叠排列ToolStripMenuItem });
            menuStrip1.Location = new Point(0, 0);
            menuStrip1.Name = "menuStrip1";
            menuStrip1.Size = new Size(484, 25);
            menuStrip1.TabIndex = 1;
            menuStrip1.Text = "menuStrip1";
            // 
            // 水平平铺ToolStripMenuItem
            // 
            水平平铺ToolStripMenuItem.Name = "水平平铺ToolStripMenuItem";
            水平平铺ToolStripMenuItem.Size = new Size(68, 21);
            水平平铺ToolStripMenuItem.Text = "水平平铺";
            水平平铺ToolStripMenuItem.Click += 水平平铺ToolStripMenuItem_Click;
            // 
            // 垂直平铺ToolStripMenuItem
            // 
            垂直平铺ToolStripMenuItem.Name = "垂直平铺ToolStripMenuItem";
            垂直平铺ToolStripMenuItem.Size = new Size(68, 21);
            垂直平铺ToolStripMenuItem.Text = "垂直平铺";
            // 
            // 层叠排列ToolStripMenuItem
            // 
            层叠排列ToolStripMenuItem.Name = "层叠排列ToolStripMenuItem";
            层叠排列ToolStripMenuItem.Size = new Size(68, 21);
            层叠排列ToolStripMenuItem.Text = "层叠排列";
            // 
            // Form1
            // 
            AutoScaleDimensions = new SizeF(7F, 17F);
            AutoScaleMode = AutoScaleMode.Font;
            ClientSize = new Size(484, 461);
            Controls.Add(menuStrip1);
            IsMdiContainer = true;
            MainMenuStrip = menuStrip1;
            Name = "Form1";
            SizeGripStyle = SizeGripStyle.Hide;
            Text = "Form1";
            Load += Form1_Load;
            menuStrip1.ResumeLayout(false);
            menuStrip1.PerformLayout();
            ResumeLayout(false);
            PerformLayout();
        }

        #endregion

        private MenuStrip menuStrip1;
        private ToolStripMenuItem 水平平铺ToolStripMenuItem;
        private ToolStripMenuItem 垂直平铺ToolStripMenuItem;
        private ToolStripMenuItem 层叠排列ToolStripMenuItem;
    }
}

（2）鼠标依次点击控件菜单项“垂直平铺”、“层叠排列”

继续观察窗体设计生成器自动新增内容和Form1.cs自动新增的内容。

//Form1.cs
namespace App3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        //在Form1_Load()中显示所有子窗体
        private void Form1_Load(object sender, EventArgs e)
        {

            Form2 frm2 = new()//自动加载Form2
            {
                MdiParent = this
            };
            frm2.Show();
            Form3 frm3 = new()//自动加载Form3
            {
                MdiParent = this
            };
            frm3.Show();
            Form4 frm4 = new()//自动加载Form4
            {
                MdiParent = this
            };
            frm4.Show();
        }
        //激活菜单项“水平平铺”的Click事件
        private void 水平平铺ToolStripMenuItem_Click(object sender, EventArgs e)
        {

        }
        //激活菜单项“层叠排列”的Click事件
        private void 层叠排列ToolStripMenuItem_Click(object sender, EventArgs e)
        {

        }
        //激活菜单项“垂直平铺”的Click事件
        private void 垂直平铺ToolStripMenuItem_Click(object sender, EventArgs e)
        {

        }
    }
}

//Form1.Designer.cs
namespace App3
{
    partial class Form1
    {
        /// <summary>
        ///  Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        ///  Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        ///  Required method for Designer support - do not modify
        ///  the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            menuStrip1 = new MenuStrip();
            水平平铺ToolStripMenuItem = new ToolStripMenuItem();
            垂直平铺ToolStripMenuItem = new ToolStripMenuItem();
            层叠排列ToolStripMenuItem = new ToolStripMenuItem();
            menuStrip1.SuspendLayout();
            SuspendLayout();
            // 
            // menuStrip1
            // 
            menuStrip1.Items.AddRange(new ToolStripItem[] { 水平平铺ToolStripMenuItem, 垂直平铺ToolStripMenuItem, 层叠排列ToolStripMenuItem });
            menuStrip1.Location = new Point(0, 0);
            menuStrip1.Name = "menuStrip1";
            menuStrip1.Size = new Size(484, 25);
            menuStrip1.TabIndex = 1;
            menuStrip1.Text = "menuStrip1";
            // 
            // 水平平铺ToolStripMenuItem
            // 
            水平平铺ToolStripMenuItem.Name = "水平平铺ToolStripMenuItem";
            水平平铺ToolStripMenuItem.Size = new Size(68, 21);
            水平平铺ToolStripMenuItem.Text = "水平平铺";
            水平平铺ToolStripMenuItem.Click += 水平平铺ToolStripMenuItem_Click; //激活点击事件
            // 
            // 垂直平铺ToolStripMenuItem
            // 
            垂直平铺ToolStripMenuItem.Name = "垂直平铺ToolStripMenuItem";
            垂直平铺ToolStripMenuItem.Size = new Size(68, 21);
            垂直平铺ToolStripMenuItem.Text = "垂直平铺";
            垂直平铺ToolStripMenuItem.Click += 垂直平铺ToolStripMenuItem_Click; //激活点击事件
            // 
            // 层叠排列ToolStripMenuItem
            // 
            层叠排列ToolStripMenuItem.Name = "层叠排列ToolStripMenuItem";
            层叠排列ToolStripMenuItem.Size = new Size(68, 21);
            层叠排列ToolStripMenuItem.Text = "层叠排列";
            层叠排列ToolStripMenuItem.Click += 层叠排列ToolStripMenuItem_Click; //激活点击事件
            // 
            // Form1
            // 
            AutoScaleDimensions = new SizeF(7F, 17F);
            AutoScaleMode = AutoScaleMode.Font;
            ClientSize = new Size(484, 461);
            Controls.Add(menuStrip1);
            IsMdiContainer = true;
            MainMenuStrip = menuStrip1;
            Name = "Form1";
            SizeGripStyle = SizeGripStyle.Hide;
            Text = "Form1";
            Load += Form1_Load;
            menuStrip1.ResumeLayout(false);
            menuStrip1.PerformLayout();
            ResumeLayout(false);
            PerformLayout();
        }

        #endregion

        private MenuStrip menuStrip1;
        private ToolStripMenuItem 水平平铺ToolStripMenuItem;
        private ToolStripMenuItem 垂直平铺ToolStripMenuItem;
        private ToolStripMenuItem 层叠排列ToolStripMenuItem;
    }
}

（3）添加点击事件属性

在Form1.cs中添加事件属性，从而完成点击控件后执行的操作。

//Form1.cs
namespace App3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        //在Form1_Load()中显示所有子窗体
        private void Form1_Load(object sender, EventArgs e)
        {

            Form2 frm2 = new()//自动加载Form2
            {
                MdiParent = this
            };
            frm2.Show();
            Form3 frm3 = new()//自动加载Form3
            {
                MdiParent = this
            };
            frm3.Show();
            Form4 frm4 = new()//自动加载Form4
            {
                MdiParent = this
            };
            frm4.Show();
        }
        //激活菜单项“水平平铺”的Click事件
        private void 水平平铺ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            LayoutMdi(MdiLayout.TileHorizontal);    //添加点击事件的属性
        }
        //激活菜单项“层叠排列”的Click事件
        private void 层叠排列ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            LayoutMdi(MdiLayout.Cascade);           //添加点击事件的属性
        }
        //激活菜单项“垂直平铺”的Click事件
        private void 垂直平铺ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            LayoutMdi(MdiLayout.TileVertical);      //添加点击事件的属性
        }
    }
}