P/Invoke 改变传递参数的值

Question

所以我在 DLL 中有这个 c++ 函数

__declspec(dllexport) MOUSERAWDATA __stdcall GetMouseRawData(LPARAM lParam)
{
    UINT bufferSize = 0;
    BYTE *buffer = new BYTE[bufferSize];
    GetRawInputData((HRAWINPUT)lParam, RID_INPUT, NULL, &bufferSize, sizeof(RAWINPUTHEADER));
    GetRawInputData((HRAWINPUT)lParam, RID_INPUT, (LPVOID)buffer, &bufferSize, sizeof(RAWINPUTHEADER));
    RAWINPUT *raw = (RAWINPUT*)buffer;
    MOUSERAWDATA data;
    if (raw->header.dwType == RIM_TYPEMOUSE)
    {
        data.longX = raw->data.mouse.lLastX;
        data.longY = raw->data.mouse.lLastY;
    }
    return data;
}

以下是在我的 c# 项目中：

[DllImport("RawInput.dll", CallingConvention = CallingConvention.StdCall)]
private static extern MouseRawData GetMouseRawData(IntPtr lParam);
.
.
.
protected override void WndProc(ref Message m)
{
    switch(m.Msg)
    {
        case WM_CREATE:
            if (AttachMouseListener(this.Handle))
                Console.WriteLine("It works!");
            break;
        case WM_INPUT:
            MouseRawData data = GetMouseRawData(m.LParam);
            break;
        default:
            base.WndProc(ref m);
            break;
     }
}

当我运行这段代码时，以下值被传递给 GetMouseRawData

但由于某种原因，lParam 在 C++ 端的值总是不同的。

我本例 0x004fe95c = 5237084

有人知道为什么会这样吗？

Answer 1

您正在分配一个长度为 0 的缓冲区。然后“询问”缓冲区的大小。然后通过告诉他们您的缓冲区大小正确来欺骗 GetRawInputData。将缓冲区分配移动到第一次调用后您已了解所需缓冲区大小的位置。

UINT bufferSize = 0;
BYTE *buffer = new BYTE[bufferSize];
GetRawInputData((HRAWINPUT)lParam, RID_INPUT, NULL, &bufferSize, sizeof(RAWINPUTHEADER));
GetRawInputData((HRAWINPUT)lParam, RID_INPUT, (LPVOID)buffer, &bufferSize, sizeof(RAWINPUTHEADER));
RAWINPUT *raw = (RAWINPUT*)buffer;

您需要delete[] 您的缓冲区以防止泄漏。 您需要初始化data (MOUSERAWDATA) 以防止它有条件地包含垃圾。调用者如何知道raw->header.dwType == RIM_TYPEMOUSE 是真是假？

您是否考虑过根据Microsoft guidance 直接调用 GetRawInputData()：

public static extern int GetRawInputData(IntPtr hRawInput, RawInputCommand uiCommand, out RAWINPUT pData, ref int pcbSize, int cbSizeHeader);

protected override void WndProc(ref Message m)
{
    if (m.Msg == (int)WindowMessages.RawInput)  // WindowMessages.RawInput = 0x00FF (WM_INPUT)
    {
        RAWINPUT input = new RAWINPUT();
        int outSize = 0;
        int size = Marshal.SizeOf(typeof(RAWINPUT));

        outSize = Win32API.GetRawInputData(m.LParam, RawInputCommand.Input, out input, ref size, Marshal.SizeOf(typeof(RAWINPUTHEADER)));
        if (outSize != -1)
        {
            if (input.Header.Type == RawInputType.Mouse)
            {
                //input.Mouse.LastX;
                //input.Mouse.LastY;
            }
        }
    }
    base.WndProc(ref m);
}