在 Windows 过程中使用成员函数（使用 C++）

Question

我正在创建一个Windows应用程序。我正在尝试设置一个 Application 类并处理其中的成员函数中的事件，并预先声明该类的一个实例以在 Windows 过程中调用。

我希望看到一个白色的无响应窗口，但窗口创建返回 nullptr。这是main.cpp

#include <windows.h>
#include "WinApplication.h"

WinApplication* app;

LRESULT CALLBACK windowCallback(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    //return DefWindowProc(hwnd, uMsg, wParam, lParam);
    return app->appCallback(uMsg, wParam, lParam);
}

int WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd)
{
    app = new WinApplication();
    WNDCLASS window_class = {};
    window_class.style = CS_HREDRAW | CS_VREDRAW;
    window_class.lpszClassName = TEXT("Window Class");
    window_class.lpfnWndProc = windowCallback;
    
    // Register Class
    if (!RegisterClass(&window_class))
        return 1;
    
    // Create Window
    HWND window = CreateWindow(window_class.lpszClassName, TEXT("MyApp"), WS_OVERLAPPEDWINDOW | WS_VISIBLE, CW_USEDEFAULT, CW_USEDEFAULT, DEF_WIDTH, DEF_HEIGHT, 0, 0, hInstance, 0);
    
    app->init(window);
    while (true) {  }

    return 0;
}

这是会员回调：

LRESULT WinApplication::appCallback(UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    return 0;
}

如有任何帮助，我们将不胜感激

Answer 1

您不能 directoy 将类函数传递给 WinAPI 回调。

大多数调用回调的 WinAPI 函数也采用一个参数，您可以使用该参数来引用您的类。

很久以前我写了这个例子（在https://cplusplus.com/forum/general/170775/#msg851518），它演示了该技术：

#include <iostream>
#include <string>
#include <vector>

#ifndef NOMINMAX
#define NOMINMAX
#endif
extern "C" 
{
  #include <windows.h>
}

//----------------------------------------------------------------------------
// EnumWindows() -- return a list of toplevel window handles
class EnumerateWindows: public std::vector <HWND>
{
private:
  // Here's the class's callback method ......................................
  BOOL EnumWindowsMethod( HWND hWnd )
  {
    push_back( hWnd );
    return TRUE;
  }

  // Here's the static callback procedure ....................................
  static BOOL CALLBACK EnumWindowsProc( HWND hWnd, LPARAM lParam )
  {
    return reinterpret_cast <EnumerateWindows*> (lParam)->EnumWindowsMethod( hWnd );
  }
  
public:
  // Here's the function that makes it all happen ............................
  EnumerateWindows()
  {
    EnumWindows( EnumWindowsProc, (LPARAM)this );
  }
};

//----------------------------------------------------------------------------
// GetWindowText() -- return a window's titlebar text
std::string GetWindowText( HWND hWnd )
{
  std::string s( MAX_PATH, '\0' );
  s.resize( GetWindowText( hWnd, const_cast <char*> (s.c_str()), MAX_PATH ) );
  return s;
}

//----------------------------------------------------------------------------
int main()
{
  std::cout << "Toplevel windows (that actually have titles) are:\n";
  for (const auto& handle : EnumerateWindows())
  {
    const std::string& title = GetWindowText( handle );
    if (!title.empty())
      std::cout << "  \"" << title << "\"\n";
  }
}