在web页面上我们可以通过frameset,iframe嵌套框架很容易实现各种导航+内容的布局界面，而在winform、WPF中实现其实也很容易，我这里就分享一个：在winform下实现左右布局多窗口界面。

我这里说的多窗口是指一个父窗口包含多个子窗口，在winform中实现这种效果很简单，即将某个窗口的IsMdiContainer设为true,然后将其它子窗口的MdiParent设为其父窗口对象即可，这样就完成了一个多窗口界面，效果如下：

点击NEW新打开一个窗口，其效果如下：

请看我上图红色标注的地方，Windows菜单项下面显示的是当前所有已打开的子窗口，点击某个菜单，即可快速切换到其它窗口，若关闭某个子窗口，与之相对应的菜单项也会自动被移除，实现这个功能也很简单，只需要将菜单的MdiWindowListItem属性设为需要显示活动窗口列表的菜单项即可，如：this.menuStrip1.MdiWindowListItem = this.windowsToolStripMenuItem;

上述示例完整的实现代码如下：

    public partial class FormMdi : Form{private int formCount = 0;public FormMdi(){InitializeComponent();this.menuStrip1.MdiWindowListItem = this.windowsToolStripMenuItem;}private void newToolStripMenuItem_Click(object sender, EventArgs e){ShowChildForm<FormChild>();}private void ShowChildForm<TForm>() where TForm : Form, new(){TForm childForm = new TForm();childForm.Name = "frm" + Guid.NewGuid().ToString("N");childForm.Text = string.Format("Child Form -{0}", ++formCount);childForm.MdiParent = this;childForm.WindowState = FormWindowState.Maximized;childForm.Show();}}

相信实现上面这部份功能一般用过winform的人都会操作，我这里就当是复习顺便给新手一个参考，同时也为下面要实现的左右布局功能做一个铺垫吧。

要实现左右布局，并且能够支持可动态调整左右占比的功能，非SplitContainer控件莫属了，如果不了解该控件用法请自行在网上查找相关资料，我这里就不作说明，如果要显示WINDOWS已打开的子窗口情况，同样也需要用到MenuStrip控件，

最终设计的主窗口（FormMain）效果如下：

我这里因为只是演示，所以菜单控件上我只添加了两个菜单项，分别为：WINDOWS，用于显示WINDOWS已打开的子窗口列表，NEW，用于打开一个子窗口；SplitContainer控件全部采用默认的，没有放置任何控件在其中，如果用在正式系统中，一般左边Panel1中会放置一个树形菜单，右边Panel2中保持空即可，因为这个是用来作为子窗口的容器。

控件层次结构如下图示：

界面设计好了，下面就实现最重要的两个功能。

第一个功能：在右边Panel2中显示子窗口，实现代码如下：

public FormMain()｛this.IsMdiContainer = true;｝private void ShowChildForm<TForm>() where TForm : Form, new(){TForm childForm = new TForm();childForm.Name = "frm" + Guid.NewGuid().ToString("N");childForm.Text = string.Format("Child Form -{0}", ++formCount);childForm.MdiParent = this;childForm.Parent = splitContainer1.Panel2;childForm.WindowState = FormWindowState.Maximized;childForm.Show();}

简要说明:

1.在窗口构造函数中动态的将IsMdiContainer设为true,当然也可以设计视图中设置；

2.编写一个显示写子窗口的方法，方法中需注意的地方：childForm.MdiParent = this；childForm.Parent = splitContainer1.Panel2，意思是：将当前窗口作为子窗口的父窗口，同时将Panel2指定为子窗口的父对象，这样就能实现子窗口在Panel2中打开了。

第二个功能：在WINDOWS菜单项下显示已打开的子窗口列表，这里实现就没有像文章一开始介绍的那样简单，使用那个方法是无效的，需要我们来自行实现，稍微有点复杂，但如果明白其实现原理，也就简单明白了。

实现思路：当childForm加载到Panel2时，会触发Panel2.ControlAdded事件，当childForm被关闭时，会触发Panel2.ControlRemoved事件，我们可以统一订阅这两个事件，当childForm加载时，那么就在WINDOWS菜单项下增加一个菜单项，反之则移除该菜单项，实现代码如下：

this.splitContainer1.Panel2.ControlAdded += Panel2_ControlChanged;
this.splitContainer1.Panel2.ControlRemoved += Panel2_ControlChanged;void Panel2_ControlChanged(object sender, ControlEventArgs e){var frm = e.Control as Form;string menuName = "menu_" + frm.Name;bool exists = this.splitContainer1.Panel2.Controls.Contains(frm);if (exists){var menuItem = GetMenuItem(menuName);if (menuItem != null){menuItem.Checked = true;frm.BringToFront();frm.Focus();}else{windowsToolStripMenuItem.DropDownItems.Add(new ToolStripMenuItem() { Text = frm.Text, Name = menuName, Tag = frm, Checked = true });}}else{var menuItem = GetMenuItem(menuName);if (menuItem != null){windowsToolStripMenuItem.DropDownItems.Remove(menuItem);menuItem.Dispose();}}}private ToolStripMenuItem GetMenuItem(string menuName){var menuItems = windowsToolStripMenuItem.DropDownItems.Cast<ToolStripMenuItem>();menuItems.ToList().ForEach(m => m.Checked = false);return menuItems.Where(m => m.Name == menuName).SingleOrDefault();}

同时为了实现点击WINDOWS菜单项的子菜单能够快速切换子窗口，需要订阅WINDOWS菜单项的DropDownItemClicked事件，当然也可以为新增的子菜单项订阅Click事件，实现代码如下：

windowsToolStripMenuItem.DropDownItemClicked += windowsToolStripMenuItem_DropDownItemClicked;void windowsToolStripMenuItem_DropDownItemClicked(object sender, ToolStripItemClickedEventArgs e){var menuItem = GetMenuItem(e.ClickedItem.Name);menuItem.Checked = true;var childForm = menuItem.Tag as Form;childForm.BringToFront();childForm.Focus();}private void CheckWindowsMenuItem(string menuName){var menuItem = GetMenuItem(menuName);if (menuItem != null){menuItem.Checked = true;}}

这样就基本实现了在WINDOWS菜单项下显示已打开的子窗口列表，并点击指定的菜单项能够切换当前活动的子窗口，但仍有一个不足的地方，那就是，当直接点击子窗口来切换当前活动窗口时（说白了就是当点击某个子窗口标题栏，该窗口就显示在其它所有的子窗口最前面），WINDOWS菜单项下的子菜单勾选项没有同步更新，一开始想到的是用Activated事件来进行处理，结果经测试发现有效，该Activated事件在点击子窗口标题栏时并不会被触发，所以只能换种方法，经过多次测试，发现当窗口从后面切换到前面时（称为Z顺序改变），子窗口就会发生重绘，从而触发Paint方法，我们可以订阅该事件，并进行处理，实现代码如下：

private string currentChildFormName = null;   //记录当前活动子窗口名称childForm.Paint += (s, e) => { var frm=s as Form;if (!frm.Name.Equals(currentChildFormName) && this.splitContainer1.Panel2.Controls[0].Equals(frm)) //当容器中第一个控件就是当前的窗口，则表明该窗口处于所有窗口之上{CheckWindowsMenuItem("menu_" + frm.Name);currentChildFormName = frm.Name;}};

最后贴出完整的实现代码：

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 WindowsFormsApplication1
{public partial class FormMain : Form{private int formCount = 0;private string currentChildFormName = null;public FormMain(){InitializeComponent();this.IsMdiContainer = true;this.splitContainer1.Panel2.ControlAdded += Panel2_ControlChanged;this.splitContainer1.Panel2.ControlRemoved += Panel2_ControlChanged;windowsToolStripMenuItem.DropDownItemClicked += windowsToolStripMenuItem_DropDownItemClicked;}void windowsToolStripMenuItem_DropDownItemClicked(object sender, ToolStripItemClickedEventArgs e){var menuItem = GetMenuItem(e.ClickedItem.Name);menuItem.Checked = true;var childForm = menuItem.Tag as Form;childForm.BringToFront();childForm.Focus();}private void FormMain_Load(object sender, EventArgs e){ShowChildForm<FormChild>();}private void ShowChildForm<TForm>() where TForm : Form, new(){TForm childForm = new TForm();childForm.Name = "frm" + Guid.NewGuid().ToString("N");childForm.Text = string.Format("Child Form -{0}", ++formCount);childForm.MdiParent = this;childForm.Parent = splitContainer1.Panel2;childForm.WindowState = FormWindowState.Maximized;childForm.Paint += (s, e) => { var frm=s as Form;if (!frm.Name.Equals(currentChildFormName) && this.splitContainer1.Panel2.Controls[0].Equals(frm)) //当容器中第一个控件就是当前的窗口，则表明该窗口处于所有窗口之上{CheckWindowsMenuItem("menu_" + frm.Name);currentChildFormName = frm.Name;}};childForm.Show();}private void CheckWindowsMenuItem(string menuName){var menuItem = GetMenuItem(menuName);if (menuItem != null){menuItem.Checked = true;}}void Panel2_ControlChanged(object sender, ControlEventArgs e){var frm = e.Control as Form;string menuName = "menu_" + frm.Name;bool exists = this.splitContainer1.Panel2.Controls.Contains(frm);if (exists){var menuItem = GetMenuItem(menuName);if (menuItem != null){menuItem.Checked = true;frm.BringToFront();frm.Focus();}else{windowsToolStripMenuItem.DropDownItems.Add(new ToolStripMenuItem() { Text = frm.Text, Name = menuName, Tag = frm, Checked = true });}}else{var menuItem = GetMenuItem(menuName);if (menuItem != null){windowsToolStripMenuItem.DropDownItems.Remove(menuItem);menuItem.Dispose();}}}private ToolStripMenuItem GetMenuItem(string menuName){var menuItems = windowsToolStripMenuItem.DropDownItems.Cast<ToolStripMenuItem>();menuItems.ToList().ForEach(m => m.Checked = false);return menuItems.Where(m => m.Name == menuName).SingleOrDefault();}private void newToolStripMenuItem_Click(object sender, EventArgs e){ShowChildForm<FormChild>();}}
}

以下是系统自动生成的代码：

namespace WindowsFormsApplication1
{partial class FormMain{/// <summary>/// 必需的设计器变量。/// </summary>private System.ComponentModel.IContainer components = null;/// <summary>/// 清理所有正在使用的资源。/// </summary>/// <param name="disposing">如果应释放托管资源，为 true；否则为 false。</param>protected override void Dispose(bool disposing){if (disposing && (components != null)){components.Dispose();}base.Dispose(disposing);}#region Windows 窗体设计器生成的代码/// <summary>/// 设计器支持所需的方法 - 不要/// 使用代码编辑器修改此方法的内容。/// </summary>private void InitializeComponent(){this.menuStrip1 = new System.Windows.Forms.MenuStrip();this.windowsToolStripMenuItem = new System.Windows.Forms.ToolStripMenuItem();this.newToolStripMenuItem = new System.Windows.Forms.ToolStripMenuItem();this.splitContainer1 = new System.Windows.Forms.SplitContainer();this.menuStrip1.SuspendLayout();((System.ComponentModel.ISupportInitialize)(this.splitContainer1)).BeginInit();this.splitContainer1.SuspendLayout();this.SuspendLayout();// // menuStrip1// this.menuStrip1.Items.AddRange(new System.Windows.Forms.ToolStripItem[] {this.windowsToolStripMenuItem,this.newToolStripMenuItem});this.menuStrip1.Location = new System.Drawing.Point(0, 0);this.menuStrip1.MdiWindowListItem = this.windowsToolStripMenuItem;this.menuStrip1.Name = "menuStrip1";this.menuStrip1.Size = new System.Drawing.Size(1069, 25);this.menuStrip1.TabIndex = 1;this.menuStrip1.Text = "menuStrip1";// // windowsToolStripMenuItem// this.windowsToolStripMenuItem.Name = "windowsToolStripMenuItem";this.windowsToolStripMenuItem.Size = new System.Drawing.Size(73, 21);this.windowsToolStripMenuItem.Text = "Windows";this.windowsToolStripMenuItem.Click += new System.EventHandler(this.windowsToolStripMenuItem_Click);// // newToolStripMenuItem// this.newToolStripMenuItem.Name = "newToolStripMenuItem";this.newToolStripMenuItem.Size = new System.Drawing.Size(46, 21);this.newToolStripMenuItem.Text = "New";this.newToolStripMenuItem.Click += new System.EventHandler(this.newToolStripMenuItem_Click);// // splitContainer1// this.splitContainer1.BackColor = System.Drawing.SystemColors.ActiveCaption;this.splitContainer1.Dock = System.Windows.Forms.DockStyle.Fill;this.splitContainer1.Location = new System.Drawing.Point(0, 25);this.splitContainer1.Name = "splitContainer1";// // splitContainer1.Panel2// this.splitContainer1.Panel2.BackColor = System.Drawing.SystemColors.ScrollBar;this.splitContainer1.Size = new System.Drawing.Size(1069, 526);this.splitContainer1.SplitterDistance = 356;this.splitContainer1.TabIndex = 2;// // FormMain// this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;this.ClientSize = new System.Drawing.Size(1069, 551);this.Controls.Add(this.splitContainer1);this.Controls.Add(this.menuStrip1);this.MainMenuStrip = this.menuStrip1;this.Name = "FormMain";this.Text = "FormMain";this.Load += new System.EventHandler(this.FormMain_Load);this.menuStrip1.ResumeLayout(false);this.menuStrip1.PerformLayout();((System.ComponentModel.ISupportInitialize)(this.splitContainer1)).EndInit();this.splitContainer1.ResumeLayout(false);this.ResumeLayout(false);this.PerformLayout();}#endregionprivate System.Windows.Forms.MenuStrip menuStrip1;private System.Windows.Forms.ToolStripMenuItem windowsToolStripMenuItem;private System.Windows.Forms.SplitContainer splitContainer1;private System.Windows.Forms.ToolStripMenuItem newToolStripMenuItem;}
}

以下是效果演示截图：

如果大家有什么更好的实现方法可以在下方评论，不足之处也欢迎指出，谢谢！