private void InitRichTextBoxContextMenu(RichTextBox textBox)
{
    //创建剪切子菜单
    var cutMenuItem = new MenuItem( "剪切");
    cutMenuItem.Click += (sender, eventArgs) => textBox.Cut();

    //创建复制子菜单
    var copyMenuItem = new MenuItem( "复制");
    copyMenuItem.Click += (sender, eventArgs) => textBox.Copy();

    //创建粘贴子菜单
    var pasteMenuItem = new MenuItem( "粘贴");
    pasteMenuItem.Click += (sender, eventArgs) => textBox.Paste();

    //创建右键菜单并将子菜单加入到右键菜单中
    var contextMenu = new ContextMenu();
    contextMenu.MenuItems.Add(cutMenuItem);
    contextMenu.MenuItems.Add(copyMenuItem);
    contextMenu.MenuItems.Add(pasteMenuItem);

    textBox.ContextMenu = contextMenu; //为richtextbox设置菜单
}