类似excel表格中各个表单sheet的切换效果，使用tabcontrol控件实现类似的功能。效果如下：

过程涉及父窗体MDIParent1、子窗体main、自定义基础功能类MdiChildBase。

基础功能类MdiChildBase继承自Form创建，定义了一个委托SetTabControlDelegate，委托的实例SetTabI用于指定FormClosing和Shown方法中调用的方法（函数），添加了窗口的FormClosing和Shown处理方法，窗口再打开和关闭的时候会被调用，即后面继承MdiChildBase创建的子窗体会在窗口关闭和显示的时候执行相应方法。可见，委托的实例SetTabI起到重要的连接作用。

子窗体main是自己创建的窗体，继承自类MdiChildBase，其他用于子窗体的Form也需要继承类MdiChildBase：“public partial class Main : MdiChildBase”，在窗口的关闭和显示过程中会执行MdiChildBase中注册的FormClosing和Shown方法，调用父窗体MDIParent1的SetTabControl方法添加和移除对应窗口的tab标签；

父窗体MDIParent1为MDI父窗体，包含一个用户显示子窗体列表的tabcontrol控件，定义了SetTabControl方法添加和移除对应窗口的tab标签；

主要代码

父窗体MDIParent1：

MDIParent父窗体设置为MDI容器窗体：this.IsMdiContainer = true;

MDIParent父窗体的Designer中tabControl控件的主要属性设置：

// 
// tabControl1
// 
this.tabControl1.Dock = System.Windows.Forms.DockStyle.Bottom;
this.tabControl1.Location = new System.Drawing.Point(0, 496);
this.tabControl1.Name = "tabControl1";
this.tabControl1.SelectedIndex = 0;
this.tabControl1.ShowToolTips = true;
this.tabControl1.Size = new System.Drawing.Size(992, 18);
this.tabControl1.TabIndex = 4;
this.tabControl1.Visible = false;
this.tabControl1.SelectedIndexChanged += new System.EventHandler(this.tabControl1_SelectedIndexChanged);

MDIParent：

public partial class MDIParent1 : Form
{private void MDIParent1_Load(object sender, EventArgs e){MdiChildBase.SetTabII = this.SetTabControl;LoadMdiForm(typeof(Main));}public void LoadMdiForm(Type formType){Form w = Application.OpenForms[formType.Name];bool exists = false;MdiChildBase mdiChild = null;if (w != null){exists = true;mdiChild = w as MdiChildBase;}if (!exists){mdiChild = (MdiChildBase)Activator.CreateInstance(formType, true);mdiChild.MdiParent = this;mdiChild.Show();}mdiChild.SetTabI = SetTabControl;mdiChild.BringToFront();mdiChild.Activate();}public void SetTabControl(string type,string name){ if(type=="add"){TabPage page= new TabPage();page.Text = name;page.Name = name;tabControl1.TabPages.Add(page);tabControl1.SelectedTab = page;if (tabControl1.TabPages.Count > 0) tabControl1.Visible = true ;}else if (type=="remove"){TabPage tab = tabControl1.TabPages[name];if(tab != null)tabControl1.TabPages.Remove(tab);if (tabControl1.TabPages.Count == 0) tabControl1.Visible = false;}else if (type=="select"){TabPage page = tabControl1.TabPages[name];tabControl1.SelectedTab = page;}}private void tabControl1_SelectedIndexChanged(object sender, EventArgs e){if (tabControl1.SelectedTab == null) return;string WindowsName = tabControl1.SelectedTab.Text;// MdiChildrenForm w = Application.OpenForms[WindowsName];//判断对应窗口是否被打开//if ((w == null) || (w.IsDisposed))w.Activate();//w.Show();//w.WindowState = FormWindowState.Normal;}
}

子窗体main：

public partial class Main : MdiChildBase
{public Main(){CheckForIllegalCrossThreadCalls = false;InitializeComponent();}private void Form1_Load(object sender, EventArgs e){}
}

 MdiChildBase：

public class MdiChildBase:Form
{public MdiChildBase(){this.FormClosing += new FormClosingEventHandler(baseFormClosing);this.Shown += new EventHandler(baseFormShown);}/// <summary>/// 主要用于MDI父窗体中窗口列表的显示/// </summary>/// <param name="type"></param>/// <param name="name"></param>public delegate void SetTabControlDelegate(string type, string name);//用于从mdiparent主窗口发起的窗口FormClosing、Shown过程中对窗口列表的添加删除；public SetTabControlDelegate SetTabI;//用于从其他非mdiparent主窗口发起的窗口生成，在mdiparent主窗口load中设置了方法名称；//即：mdiparent主窗口实例存在的话，会在子窗口中的FormClosing和Shown过程中执行对应的方法；//    若主窗口不是从 mdiparent主窗口开始运行，则不存在MDI父窗体，SetTabII为null，也不会执行对应方法public static SetTabControlDelegate SetTabII;   //public Action<string,string> SetTabI;//public static Action<string, string> SetTabII;public virtual void baseFormClosing(object sender, EventArgs e){//SetTabI?.Invoke("remove", this.Name);if (SetTabI != null){SetTabI.Invoke("remove", this.Name);//MessageBox.Show("remove");}}public virtual void baseFormShown(object sender, EventArgs e){//SetTabI?.Invoke("add", this.Name);if (SetTabI != null){SetTabI.Invoke("add", this.Name);//MessageBox.Show("add");}}}

代码复用问题

上面所说的是针对父窗体包含子窗体的使用方式，在实际中会存在一个窗体可用于子窗体，也可用于单独窗体或单独项目中的启动窗体，如下面的窗体“数据对比”，它继承自MdiChildBase创建，当它用于一个不包含MDIParent的项目中（不包含对MDIParent的引用，因为MDIParent做为主窗体，可能所在项目包含了对所有窗体/类的引用），可借助MdiChildBase中的委托实例SetTabII来进行区分，具体信息见MdiChildBase类中SetTabII的文字说明。

//Form f = Application.OpenForms["数据对比"];
数据对比 f = new 数据对比(dt);
Form mDIParent = Application.OpenForms["MDIParent1"];
MDIParent1 mDIParent1 = Application.OpenForms["MDIParent1"] as MDIParent1;MdiChildBase mdiChild = null;
if (f != null)
{f.MdiParent = mDIParent;mdiChild = f as MdiChildBase;
}
else
{mdiChild = (MdiChildBase)Activator.CreateInstance(typeof(数据对比), true);mdiChild.MdiParent = mDIParent;
}mdiChild.SetTabI = MdiChildBase.SetTabII;
mdiChild.Show();
mdiChild.BringToFront();
mdiChild.Activate();