使用XtraTabbedMdiManager后如何给Mdi窗体添加背景图片

使用XtraTabbedMdiManager控件管理Mdi里面的窗体后，发现背景图片不能显示，
重写DevExpress.XtraTabbedMdi.XtraTabbedMdiManager的DrawNC方法就行了。
using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using System.ComponentModel;

namespace MdiForm
{
    public class TabbedMdiManager : DevExpress.XtraTabbedMdi.XtraTabbedMdiManager
    {
        Image _backImage = null;

        public TabbedMdiManager(): base()
        {
        }

        public TabbedMdiManager(IContainer container) : base(container)
        {
        }

        public Image BackImage
        {
            set { _backImage = value; }
            get { return _backImage; }
        }

        protected override void DrawNC(DevExpress.Utils.Drawing.DXPaintEventArgs e)
        {
            if (this.Pages.Count > 0 || _backImage == null)
            {
                base.DrawNC(e);
            }
            else
            {
                e.Graphics.DrawImage(_backImage, Bounds);
            }
        }

    }
}

在MdiForm中：
       public FrmMian()
        {
            // Required for Windows Form Designer support
            InitializeComponent();

            // TODO: Add any constructor code after InitializeComponent call
            InitTabbedMdiManager();
        }

        public void InitTabbedMdiManager()
        {
            TabbedMdiManager TabbedMdiManager1 = new TabbedMdiManager();
            TabbedMdiManager1.MdiParent = this;
            TabbedMdiManager1.BackImage = MdiForm.Properties.Resources.BackgroundImage;       
         }

如果没有使用XtraTabbedMdiManager控件 ，在构造函数中添加：
       public FrmMian()
        {
            // Required for Windows Form Designer support
            InitializeComponent();

            foreach (Control var in this.Controls)
            {
                if (var is MdiClient)
                {
                    var.BackgroundImage = MdiForm.Properties.Resources.BackgroundImage;
                    var.BackgroundImageLayout = ImageLayout.Stretch;
                    break;
                }
            }
        }