WindowFromPoint的返回值是0怎么处理

[StructLayout (LayoutKind.Sequential)]
        public class point
        {

            public int  x;
            public int  y;
            public point(int  _x, int  _y)
            {

                x = _x;
                y = _y;
            }
        }
 point _point = Control.MousePosition;
                    IntPtr hwyunyong = WindowFromPoint(_point);
hwyunyong 值总是为0 ，怎么处理？谢谢 --------------------编程问答-------------------- 本身没看出有什么错。

    // 按着鼠标移动看效果

    public Form1()

    {

        InitializeComponent();

        this.MouseMove += delegate { this.Text = "Handle:" + WindowFromPoint(Control.MousePosition); };

    }



    [DllImport("user32.dll", SetLastError=true)]

    static extern IntPtr WindowFromPoint(System.Drawing.Point Point);

--------------------编程问答--------------------

补充：.NET技术 ,  C#