Object oriented c++ win32?

Question

I want to create my own class to handle creating windows and the window procedure but I have noticed that the window procedure has to be static! I'm now wondering whether its possible to make the window procedure object oriented? I have read some tutorials on object oriented windows, but they always make the procedure static -.- whats the use in that? :/

Any links or info on how to get around this problem would be appreciated,

thanks

Answer 1

You can get around that by making the static WndProc delegate everything to the members:

// Forward declarations
class MyWindowClass;
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)

std::map<HWND, MyWindowClass *> windowMap;

// Your class
class MyWindowClass  {
private:
  HWND m_handle;

  // The member WndProc
  LRESULT MyWndProc(UINT message, WPARAM wParam, LPARAM lParam) { /* ... */ }

public:
  MyWindowClass()
  {
    /* TODO: Create the window here and assign its handle to m_handle */
    /* Pass &WndProc as the pointer to the Window procedure */

    // Register the window
    windowMap[m_handle] = this;
  }
};

// The delegating WndProc
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
  std::map<HWND, MyWindowClass *>::iterator it = windowMap.find(hWnd);
  if (it != windowMap.end())
    return it->second->MyWndProc(message, wParam, lParam);
  return 0;
}

Answer 2

The general technique of allowing a window instance to be represented by as class instance is to make use of the SetWindowLongPtr and GetWindowLongPtr to associate your class instance pointer with the window handle. Below is some sample code to get you started. It may not compile without a few tweaks. It's only meant to be a reference.

Personally, I've stopped rolling my own window classes back a few years ago when I discovered ATL's CWindow and CWindowImpl template class. They take care of doing all this mundane coding for you so can focus on just writing methods that handle window messages. See the example code I wrote up here.

Hope this helps.

class CYourWindowClass
{
private:
    HWND m_hwnd;

public:
    LRESULT WndProc(UINT uMsg, WPARAM wParam, LPARAM lParam)
    {
        switch (uMsg)
        {
            case WM_CREATE: return OnCreate(wParam, lParam);
            case wM_PAINT: return OnPaint(wParam, lParam);
            case WM_DESTROY:
            {
                SetWindowLongPtr(m_hwnd, GWLP_USERDATA, NULL);
                m_hwnd = NULL;
                return 0;
            }
        }
        return DefWindowProc(m_hwnd, uMsg, wParam, lParam);

    }

    CYourWindowClass()
    {
        m_hwnd = NULL;
    }

    ~CYourWindowClass()
    {
        ASSERT(m_hwnd == NULL && "You forgot to destroy your window!");
        if (m_hwnd)
        {
            SetWindowLong(m_hwnd, GWLP_USERDATA, 0);
        }
    }

    bool Create(...) // add whatever parameters you want
    {
        HWND hwnd = CreateWindow("Your Window Class Name", "Your Window title", dwStyle, x, y, width, height, NULL, hMenu, g_hInstance, (LPARAM)this);
        if (hwnd == NULL)
            return false;

        ASSERT(m_hwnd == hwnd);
        return true;
    }


    static LRESULT __stdcall StaticWndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
    {
        CYourWindowClass* pWindow = (CYourWindowClass*)GetWindowLongPtr(hwnd, GWLP_USERDATA);

        if (uMsg == WM_CREATE)
        {
            pWindow = ((CREATESTRUCT*)lParam)->lpCreateParams;
            SetWindowLongPtr(hwnd, GWLP_USERDATA, (void*)pWindow);
            m_hWnd = hwnd;
        }

        if (pWindow != NULL)
        {
            return pWindow->WndProc(uMsg, wParam, lParam);
        }

        return DefWindowProc(hwnd, uMsg, wParam, lParam);
    };


};

Answer 3

If you are looking for object oriented Win32 API then you should look to MFC and/or WTL.

Answer 4

Just to add to Brian's answer but for a win32 framework that's more beginner friendly take a look at Win32++. The library itself isn't as comprehensive in features compared to MFC or QT but that is a tradeoff the designer made at the beginning to keep the library easy to understand and simple to use.

If you're still interested in this topic, I highly encourage you to take a look at it since it uses yet another technique for saving the 'this' pointer by utilizing thread local storage.

Answer 5

You can use the window handle passed to the WindowProc to grab an object you've created for that particular window and delegate the event handling to that object.

e.g.

IMyWindowInterface* pWnd = getMyWindowObject(hWnd);
pWnd->ProcessMessage(uMsg, wParam, lParam);