求教在当前或指定窗口绘制网格（涉winapi）

[PCCYC]

API已经导入。
代码也完成，但是界面没任何反应。
代码片段如下：

  public Form1()
        {
            InitializeComponent();
        }

        [DllImport("user32.dll", EntryPoint = "FindWindow")]
        private extern static IntPtr FindWindow(string lpClassName, string lpWindowName);

        [DllImport("user32.dll")]
        private static extern int GetWindowRect(IntPtr hwnd, out Rect lpRect);

        public struct Rect
        {
            public int Left;
            public int Top;
            public int Right;
            public int Bottom;
        }


        [StructLayout(LayoutKind.Sequential)]
        struct PAINTSTRUCT
        {
            public IntPtr hdc;
            public bool fErase;
            public RECT rcPaint;
            public bool fRestore;
            public bool fIncUpdate;
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 32)]
            public byte[] rgbReserved;
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct RECT
        {
            public int Left, Top, Right, Bottom;

            public RECT(int left, int top, int right, int bottom)
            {
                Left = left;
                Top = top;
                Right = right;
                Bottom = bottom;
            }

            public RECT(System.Drawing.Rectangle r) : this(r.Left, r.Top, r.Right, r.Bottom) { }

            public int X
            {
                get { return Left; }
                set { Right -= (Left - value); Left = value; }
            }

            public int Y
            {
                get { return Top; }
                set { Bottom -= (Top - value); Top = value; }
            }

            public int Height
            {
                get { return Bottom - Top; }
                set { Bottom = value + Top; }
            }

            public int Width
            {
                get { return Right - Left; }
                set { Right = value + Left; }
            }

            public System.Drawing.Point Location
            {
                get { return new System.Drawing.Point(Left, Top); }
                set { X = value.X; Y = value.Y; }
            }

            public System.Drawing.Size Size
            {
                get { return new System.Drawing.Size(Width, Height); }
                set { Width = value.Width; Height = value.Height; }
            }

            public static implicit operator System.Drawing.Rectangle(RECT r)
            {
                return new System.Drawing.Rectangle(r.Left, r.Top, r.Width, r.Height);
            }

            public static implicit operator RECT(System.Drawing.Rectangle r)
            {
                return new RECT(r);
            }

            public static bool operator ==(RECT r1, RECT r2)
            {
                return r1.Equals(r2);
            }

            public static bool operator !=(RECT r1, RECT r2)
            {
                return !r1.Equals(r2);
            }

            public bool Equals(RECT r)
            {
                return r.Left == Left && r.Top == Top && r.Right == Right && r.Bottom == Bottom;
            }

            public override bool Equals(object obj)
            {
                if (obj is RECT)
                    return Equals((RECT)obj);
                else if (obj is System.Drawing.Rectangle)
                    return Equals(new RECT((System.Drawing.Rectangle)obj));
                return false;
            }

            public override int GetHashCode()
            {
                return ((System.Drawing.Rectangle)this).GetHashCode();
            }

            public override string ToString()
            {
                return string.Format(System.Globalization.CultureInfo.CurrentCulture, "{{Left={0},Top={1},Right={2},Bottom={3}}}", Left, Top, Right, Bottom);
            }
        }

        [DllImport("user32.dll")]
        static extern IntPtr BeginPaint(IntPtr hwnd, out PAINTSTRUCT lpPaint);

        [DllImport("user32.dll")]
        static extern bool EndPaint(IntPtr hWnd, [In] ref PAINTSTRUCT lpPaint);

        [DllImport("gdi32.dll")]
        static extern bool MoveToEx(IntPtr hdc, int X, int Y, IntPtr lpPoint);

        [DllImport("gdi32.dll")]
        static extern bool LineTo(IntPtr hdc, int nXEnd, int nYEnd);

        private delegate int HookProc(int code, IntPtr wParam, IntPtr lParam);
        static IntPtr hHook;
        IntPtr windowHandle =IntPtr.Zero;
        uint processHandle;

        HookProc PaintHookProcedure;

        [System.Runtime.InteropServices.DllImport("user32.dll", EntryPoint = "SetWindowsHookEx", SetLastError = true)]


        static extern IntPtr SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hMod, uint dwThreadId);

        [System.Runtime.InteropServices.DllImport("user32.dll")]
        static extern int CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);

        private const int WM_PAINT = 15;
        private const int WH_GETMESSAGE = 3;

        [System.Runtime.InteropServices.DllImport("user32.dll")]
        static extern uint GetWindowThreadProcessId(IntPtr hWnd, out uint lpdwProcessId);
        Rect rect;
        PAINTSTRUCT bPaintstruct;

        [DllImport("kernel32.dll")]
        static extern uint GetLastError();

        [System.Runtime.InteropServices.DllImport("kernel32.dll", CharSet = System.Runtime.InteropServices.CharSet.Auto)]
        public static extern IntPtr GetModuleHandle(string lpModuleName);

        [DllImport("user32.dll", CharSet = CharSet.Auto, ExactSpelling = true)]
        public static extern IntPtr GetForegroundWindow();

        private void button1_Click(object sender, EventArgs e)
        {

            uint processHandle;


            PaintHookProcedure = new HookProc(PaintHookProc);

            Process curProcess = Process.GetCurrentProcess();


            // windowHandle = FindWindow("Notepad", null);
            //  windowHandle = FindWindow(null, "计算器");
            IntPtr hMod = System.Runtime.InteropServices.Marshal.GetHINSTANCE(typeof(Form1).Module);
            windowHandle = GetForegroundWindow();
            MessageBox.Show($"hMod={hMod},windowHandle={windowHandle}");
   

            uint threadID = GetWindowThreadProcessId(windowHandle, out processHandle);

            //获取尺寸
            GetWindowRect(windowHandle, out rect);
            var ret = GetLastError();
            SetWindowsHookEx(WH_GETMESSAGE, PaintHookProcedure, GetModuleHandle(curProcess.MainModule.ModuleName), 0);

             ret =  GetLastError();
            MessageBox.Show($"hMod={hMod.ToString()},GetLastError={ret.ToString()},threadID={threadID}" );
        }
 protected override void WndProc(ref Message message)
        {
            switch (message.Msg)
            {
                case WH_GETMESSAGE:
                    if (windowHandle != IntPtr.Zero)
                    {
                        ThreadPool.QueueUserWorkItem(o =>
                        {
                            //触发成功
                            MessageBox.Show(DateTime.Now.ToString("ssfffff"));
                        });
                        #region 绘制网格
                        var height = rect.Top;
                        var width = rect.Left;
                        var hdc = BeginPaint(windowHandle, out bPaintstruct);
                        for (int i = 20; i < width; i = i + 20)
                        {
                            MoveToEx(hdc, i, 0, IntPtr.Zero);
                            LineTo(hdc, i, height);
                        }

                        for (int j = 20; j < height; j = j + 20)
                        {
                            MoveToEx(hdc, 0, j, IntPtr.Zero);
                            LineTo(hdc, width, j);
                        }

                        EndPaint(windowHandle, ref bPaintstruct);
                        #endregion

                    }
         

                    break;
            }
            base.WndProc(ref message);
        }

[良朋]

绘制网格其实完全可以不用API的

            //网格绘制
            pen = new Pen(Color.Green);
            pen.DashPattern = new float[] { 3f, 5f };
            //竖线
            int n = width;
            for (int i = 0; i < n; i += 30)
            {
                g.DrawLine(pen, new Point(i, 0), new Point(i, height));
                //g.ResetTransform();
                string txt = (Math.Round(i * XRate)).ToString();
                g.DrawString(txt, this.Font, brush, i - 10, 3);
            }
            //横线
            n = height;
            for (int i = 0; i < n; i += 30)
            {
                g.DrawLine(pen, new Point(0, i), new Point(width, i));
                //g.ResetTransform();
                string txt = (Math.Round(i * YRate)).ToString();
                StringFormat sf = new StringFormat();
                sf.Alignment = StringAlignment.Near;
                g.DrawString(txt, this.Font, brush, 3, i - 10, sf);
            }

[PCCYC]

引用 1 楼 良朋 的回复:

绘制网格其实完全可以不用API的

            //网格绘制
            pen = new Pen(Color.Green);
。。

谢了，XRate、YRate和brush能否给个初值，让我看看正常的效果。