将委托作为回调传递给本机 C++ API调用

Question

有人可以指出我这段代码有什么问题吗？我在混合 C++ 和 MC++ 方面经历了非常艰难的经历。我已经阅读了很多关于这个主题的博客和教程（传递委托），但现在看起来我的代码没问题（在调试模式下一步步编译和运行良好）它崩溃了。

主要问题是它需要有一个作为成员函数的委托（需要访问其他类成员）。

我记得在waveInProc文档中有一条注释说在回调中你不能调用任何系统函数。这应该是导致应用程序崩溃的原因，因为它尝试使用其他成员并且托管环境发生在此处调用其他系统方法？

ref class CWaveIn
{
public:
 void CWaveIn::Open(int currentInputDeviceId)
private:
 void AllocateBuffer(void);
 void WaveInProc(HWAVEIN hwi, UINT uMsg, DWORD_PTR dwInstance, DWORD_PTR dwParam1, DWORD_PTR dwParam2);
 delegate void CallBack(HWAVEIN hwi, UINT uMsg, DWORD_PTR dwInstance, DWORD_PTR dwParam1, DWORD_PTR dwParam2);
 CallBack^ myDelegate;
protected:
 WAVEFORMATEX* waveFormat;
 int bufferDuration; // in seconds
 BYTE* waveInBuffer;
 int bufferSize;
};

void CWaveIn::AllocateBuffer(void)
{
 free(waveInBuffer);
 bufferSize = waveFormat->nAvgBytesPerSec * bufferDuration;
 waveInBuffer = new BYTE[bufferSize];
 Debug::WriteLine("BufferSize: " + bufferSize);
}

void CWaveIn::WaveInProc(HWAVEIN hwi, UINT uMsg, DWORD_PTR dwInstance, DWORD_PTR dwParam1, DWORD_PTR dwParam2) 
{
 switch(uMsg) {
  case WIM_CLOSE:
   Debug::WriteLine("WIM_CLOSE");
   break;
  case WIM_DATA:
   for(int i=0;i<bufferSize; i++) {
    Debug::Write(waveInBuffer[i] + " ");
   }
   Debug::WriteLine("WIM_DATA");
   break;
  case WIM_OPEN:
   Debug::WriteLine("WIM_OPEN");
   break;
 }
}

void CWaveIn::Open(int currentInputDeviceId) 
{
 MMRESULT result = ::waveInOpen(0, currentInputDeviceId, waveFormat, 0, 0, WAVE_FORMAT_QUERY);
 Debug::WriteLine(L"CWaveIn::Open() WAVE_FORMAT_QUERY: device " + currentInputDeviceId.ToString());
 DebugError(result);
 if(result == MMSYSERR_NOERROR)
 {
  myDelegate = gcnew CallBack(this, &CWaveIn::WaveInProc);
  pin_ptr<CallBack^> ptrMyDelegate= &myDelegate;
  IntPtr delegatePointer = System::Runtime::InteropServices::Marshal::GetFunctionPointerForDelegate(myDelegate);

  HWAVEIN hWaveIn;
  MMRESULT result = ::waveInOpen(&hWaveIn, currentInputDeviceId, waveFormat, (DWORD_PTR)delegatePointer.ToPointer(), 0, CALLBACK_FUNCTION | WAVE_FORMAT_DIRECT);
  Debug::WriteLine(L"CWaveIn::Open() : device " + currentInputDeviceId.ToString());
  DebugError(result);

  AllocateBuffer();

  WAVEHDR WaveInHdr;
  WaveInHdr.lpData = (LPSTR)waveInBuffer;
  WaveInHdr.dwBufferLength = bufferSize;
  WaveInHdr.dwBytesRecorded=0;
  WaveInHdr.dwUser = 0L;
  WaveInHdr.dwFlags = 0L;
  WaveInHdr.dwLoops = 0L;
  ::waveInPrepareHeader(hWaveIn, &WaveInHdr, sizeof(WAVEHDR));
  result = ::waveInAddBuffer(hWaveIn, &WaveInHdr, sizeof(WAVEHDR));

  result = ::waveInStart(hWaveIn);
  Debug::WriteLine(L"CWaveIn::Start() : device " + currentInputDeviceId.ToString());
  DebugError(result);
 }
}

Answer 1

您需要使用 GCHandle 而不是 pin_ptr。请参阅 http://msdn.microsoft.com/en -us/library/367eeye0(v=vs.80).aspx

Answer 2

您在托管堆上声明 pin_ptr，然后将其传递给非托管函数
对此指针的所有托管引用都位于 CWaveIn::Open(int currentInputDeviceId) 内
所以我猜 GC 认为在 CWaveIn::Open 退出后没有理由保留这个对象。

尝试在类作用域而不是函数作用域中创建它