c# – 为什么我的高度和宽度为0？

static void Main(string[] args)
    {
        Process notePad = new Process();
        notePad.StartInfo.FileName = "notepad.exe";
        notePad.Start();
        IntPtr handle = notePad.Handle;

        RECT windowRect = new RECT();
        GetWindowRect(handle,ref windowRect);
        int width = windowRect.Right - windowRect.Left;
        int height = windowRect.Bottom - windowRect.Top;

        Console.WriteLine("Height: " + height + ",Width: " + width);
        Console.ReadLine();
    }

这是我对GetWindowRect的定义：

[DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool GetWindowRect(IntPtr hWnd,ref RECT lpRect);

这是我对RECT的定义：

[StructLayout(LayoutKind.Sequential)]
    public struct RECT
    {
        public int Left;        // x position of upper-left corner
        public int Top;         // y position of upper-left corner
        public int Right;       // x position of lower-right corner
        public int Bottom;      // y position of lower-right corner
    }

谢谢大家的帮助.