.net控件Control透明

public partial class tspControl : UserControl
    {
        public tspControl()
        {
            InitializeComponent();
            SetStyle(ControlStyles.SupportsTransparentBackColor
              | ControlStyles.UserPaint
              | ControlStyles.AllPaintingInWmPaint
              | ControlStyles.Opaque, true);
            this.BackColor = Color.Transparent;
        }       
        private Image img;
        public Image Image
        {
            get
            {
                return img;
            }
            set
            {
                img = value;
            }
        }
        protected override void OnLocationChanged(EventArgs e)
        {
            //base.OnLocationChanged(e);
            Visible = false;
            Visible = true;
        }
        protected override CreateParams CreateParams
        {
            get
            {
                //return base.CreateParams;
                CreateParams cp = base.CreateParams;
                cp.ExStyle |= 0x00000020; //WS_EX_TRANSPARENT 
                return cp;
            }
        }
        protected override void OnPaint(PaintEventArgs pe)
        {
            if (img != null)
            {
                base.OnPaint(pe);
                pe.Graphics.DrawImage(img, 0, 0);
            }
            else
            {
            }
        }
    }

//注：如果是手动改变图片，最好在刷新一下界面(this.Refresh()；)，记着图片要是透明的才能实现透明