peerconnection_client的MainWnd分析(

MainWnd中使用的就是MFC的消息机制，在此复习一下MFC吧

在MainWnd::Create()中，调用RegisterWindowClass()：

bool MainWnd::RegisterWindowClass() {
  if (wnd_class_)
    return true;

  WNDCLASSEX wcex = { sizeof(WNDCLASSEX) };
  wcex.style = CS_DBLCLKS;
  wcex.hInstance = GetModuleHandle(NULL);
  wcex.hbrBackground = reinterpret_cast<HBRUSH>(COLOR_WINDOW + 1);
  wcex.hCursor = ::LoadCursor(NULL, IDC_ARROW);
  wcex.lpfnWndProc = &WndProc;  //注册消息处理函数
  wcex.lpszClassName = kClassName;
  wnd_class_ = ::RegisterClassEx(&wcex);
  ASSERT(wnd_class_ != 0);
  return wnd_class_ != 0;
}

MainWnd中发送消息为调用：

PostMessage(wnd_, WM_COMMAND, ...)

其中wnd_为接收消息的窗口句柄，MainWnd中接收消息的函数就是上面注册的WndProc：

LRESULT CALLBACK MainWnd::WndProc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp) {
  MainWnd* me = reinterpret_cast<MainWnd*>(
      ::GetWindowLongPtr(hwnd, GWLP_USERDATA));
  if (!me && WM_CREATE == msg) {
    CREATESTRUCT* cs = reinterpret_cast<CREATESTRUCT*>(lp);
    me = reinterpret_cast<MainWnd*>(cs->lpCreateParams);
    me->wnd_ = hwnd;
    ::SetWindowLongPtr(hwnd, GWLP_USERDATA, reinterpret_cast<LONG_PTR>(me));
  }

  LRESULT result = 0;
  if (me) {
    void* prev_nested_msg = me->nested_msg_;
    me->nested_msg_ = &msg;

    bool handled = me->OnMessage(msg, wp, lp, &result);
    if (WM_NCDESTROY == msg) {
      me->destroyed_ = true;
    } else if (!handled) {
      result = ::DefWindowProc(hwnd, msg, wp, lp);
    }

    if (me->destroyed_ && prev_nested_msg == NULL) {
      me->OnDestroyed();
      me->wnd_ = NULL;
      me->destroyed_ = false;
    }

    me->nested_msg_ = prev_nested_msg;
  } else {
    result = ::DefWindowProc(hwnd, msg, wp, lp);
  }

  return result;
}