DockPanel 右键增加关闭，除此之外全部关闭的功能

在项目中新建一个class文件，代码如下:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace WeifenLuo.WinFormsUI.Docking
{
    public class DockContentEx : WeifenLuo.WinFormsUI.Docking.DockContent
    {
        private ContextMenuStrip contextMenuStrip1;
        private ToolStripMenuItem 关闭ToolStripMenuItem;
        private ToolStripMenuItem 全部关闭ToolStripMenuItem;
        private ToolStripMenuItem 除此之外全部关闭ToolStripMenuItem;
        private IContainer components;
    
        public DockContentEx()
        {
            //ContextMenuStrip cms = new System.Windows.Forms.ContextMenuStrip();
            //ToolStripMenuItem tsmiClose = new System.Windows.Forms.ToolStripMenuItem();
            //ToolStripMenuItem tsmiCloseAll = new System.Windows.Forms.ToolStripMenuItem();

            //tsmiClose.Name = "cms";
            //tsmiClose.Size = new System.Drawing.Size(98, 22);
            //tsmiClose.Text = "关闭";
            //tsmiClose.Click += new System.EventHandler(this.tsmiClose_Click);

            //cms.Items.AddRange(new System.Windows.Forms.ToolStripItem[] {tsmiClose});
            //cms.Name = "tsmiClose";
            //cms.Size = new System.Drawing.Size(99, 26);

            InitializeComponent();
            this.TabPageContextMenuStrip = contextMenuStrip1;
        }


        private void InitializeComponent()
        {
            this.components = new System.ComponentModel.Container();
            this.contextMenuStrip1 = new System.Windows.Forms.ContextMenuStrip(this.components);
            this.关闭ToolStripMenuItem = new System.Windows.Forms.ToolStripMenuItem();
            this.除此之外全部关闭ToolStripMenuItem = new System.Windows.Forms.ToolStripMenuItem();
            this.全部关闭ToolStripMenuItem = new System.Windows.Forms.ToolStripMenuItem();
            this.contextMenuStrip1.SuspendLayout();
            this.SuspendLayout();
            // 
            // contextMenuStrip1
            // 
            this.contextMenuStrip1.Items.AddRange(new System.Windows.Forms.ToolStripItem[] {
            this.关闭ToolStripMenuItem,
            this.除此之外全部关闭ToolStripMenuItem,
            this.全部关闭ToolStripMenuItem});
            this.contextMenuStrip1.Name = "contextMenuStrip1";
            this.contextMenuStrip1.ShowImageMargin = false;
            this.contextMenuStrip1.Size = new System.Drawing.Size(142, 92);
            // 
            // 关闭ToolStripMenuItem
            // 
            this.关闭ToolStripMenuItem.Name = "关闭ToolStripMenuItem";
            this.关闭ToolStripMenuItem.Size = new System.Drawing.Size(141, 22);
            this.关闭ToolStripMenuItem.Text = "关闭";
            this.关闭ToolStripMenuItem.Click += new System.EventHandler(this.关闭ToolStripMenuItem_Click);
            // 
            // 除此之外全部关闭ToolStripMenuItem
            // 
            this.除此之外全部关闭ToolStripMenuItem.Name = "除此之外全部关闭ToolStripMenuItem";
            this.除此之外全部关闭ToolStripMenuItem.Size = new System.Drawing.Size(141, 22);
            this.除此之外全部关闭ToolStripMenuItem.Text = "除此之外全部关闭";
            this.除此之外全部关闭ToolStripMenuItem.Click += new System.EventHandler(this.除此之外全部关闭ToolStripMenuItem_Click);
            // 
            // 全部关闭ToolStripMenuItem
            // 
            this.全部关闭ToolStripMenuItem.Name = "全部关闭ToolStripMenuItem";
            this.全部关闭ToolStripMenuItem.Size = new System.Drawing.Size(141, 22);
            this.全部关闭ToolStripMenuItem.Text = "全部关闭";
            this.全部关闭ToolStripMenuItem.Click += new System.EventHandler(this.全部关闭ToolStripMenuItem_Click);
            // 
            // DockContentEx
            // 
            this.ClientSize = new System.Drawing.Size(292, 273);
            this.Font = new System.Drawing.Font("SimSun", 9F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(134)));
            this.Name = "DockContentEx";
            this.contextMenuStrip1.ResumeLayout(false);
            this.ResumeLayout(false);

        }

        private void 关闭ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            this.Close();
        }

        private void 除此之外全部关闭ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            IDockContent[] documents = DockPanel.DocumentsToArray();

            foreach (IDockContent content in documents)
            {
                if (!content.Equals(this))
                {
                    content.DockHandler.Close();                    
                }
            }
        }

        private void 全部关闭ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            IDockContent[] documents = DockPanel.DocumentsToArray();

            foreach (IDockContent content in documents)
            {
                content.DockHandler.Close();
            }
        }
    }
}

其他准备以dockpanel方式打开的form都改为继承自上面这个DockPanelEx类