DLL（Windows API）中的回调？ [复制]

Question

我需要编写一个与 winmm.dll 接口的库。

https://msdn.microsoft.com/en-us/library/windows/desktop/dd798458(v=vs.85).aspx

public static class winmm {
...
   [DllImport("winmm.dll", SetLastError = true)]
   public static extern uint midiInOpen(out UIntPtr lphMidiIn, uint
      uDeviceID, UIntPtr dwCallback, UIntPtr dwCallbackInstance, uint dwFlags);
...
}

---

public void MidiInOpen() {
   winmm.midiInOpen(out midiHdl, (uint)deviceId, CALLBACK, CALLBACKINSTANCE, FLAG);
}

public void midiInCallback() {
      ...
 }

如何设置dwCallback 和dwCallbackInstance 参数？

Answer 1

关于dwCallback 使用delegate

设置

[DllImport("winmm.dll", SetLastError = true)]
private static extern MMRESULT midiInOpen(out HMIDIIN lphMidiIn, UIntPtr uDeviceID,
        MidiInProc dwCallback, UIntPtr dwCallbackInstance, MidiOpenFlags dwFlags);

[StructLayout(LayoutKind.Sequential)]
public struct HMIDIIN
{
   public IntPtr handle;
}

public enum MMRESULT : uint
{
   // General return codes.
   MMSYSERR_BASE = 0,
   MMSYSERR_NOERROR = MMSYSERR_BASE + 0,
   ...
}

public enum MidiOpenFlags : uint
{
   CALLBACK_TYPEMASK = 0x70000,
   CALLBACK_NULL = 0x00000,
   ...
}

public enum MidiInMessage : uint
{
   MIM_OPEN = 0x3C1,
   MIM_CLOSE = 0x3C2,
   ...
}

委托

public delegate void MidiInProc(HMIDIIN hMidiIn, MidiInMessage wMsg, UIntPtr dwInstance, UIntPtr dwParam1, UIntPtr dwParam2);

用法

MidiInProc dwCallback ...

public static MMRESULT midiInOpen(out HMIDIIN lphMidiIn, UIntPtr uDeviceID, MidiInProc dwCallback, UIntPtr dwCallbackInstance)
{
   return midiInOpen(out lphMidiIn, uDeviceID, dwCallback, dwCallbackInstance, dwCallback == null ? MidiOpenFlags.CALLBACK_NULL : MidiOpenFlags.CALLBACK_FUNCTION);
}

---

关于dwCallbackInstance使用GCHandle

midiInOpen function

dwCallbackInstance 传递给回调函数的用户实例数据。此参数不用于窗口回调函数或 线程。

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