WM_DESTROY not called inside wrapped WndProc - c++

Question

I have adopted the typical solution you find out there in order to use the WNDPROC as an object method, but it looks like the WM_DESTROY message is not sent to the object window's own WNDPROC and the program does not exit after closing the window.
My window class looks like this (irrelevant code removed):
class MyWindow : MyApp
{
public:
MyWindow();
void Create(void);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
private:
HWND _hWnd;
};
void MyWindow::Create()
{
// Here I register my class and call CreateWindowEx
// Everything works fine so far
// Part of the code where I assign the static WNDPROC
WNDCLASSEXW wcex;
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.style = CS_HREDRAW | CS_VREDRAW;
wcex.lpfnWndProc = MyApp::WndProc;
wcex.cbClsExtra = 0;
wcex.cbWndExtra = 0;
wcex.hInstance = this->Instance;
wcex.hIcon = LoadIcon(this->Instance, MAKEINTRESOURCE(32512));
wcex.hCursor = LoadCursor(nullptr, IDC_ARROW);
wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
wcex.lpszMenuName = NULL;
wcex.lpszClassName = "MyWindowClass";
wcex.hIconSm = LoadIcon(this->Instance, MAKEINTRESOURCE(32512));
RegisterClassExW(&wcex);
this->_hWnd = CreateWindowExW(
WS_EX_TOOLWINDOW | WS_EX_TOOLWINDOW,
wcex.lpszClassName,
"Window Title",
WS_POPUP,
10, 10,
600, 400,
nullptr,
nullptr,
this->Instance,
nullptr
);
ShowWindow(this->_hWnd, SW_SHOW);
UpdateWindow(this->_hWnd);
}
LRESULT CALLBACK MyWindow::WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
switch (msg)
{
case WM_CREATE:
{
// If I place a MessageBox here, it shows up
}
break;
case WM_DESTROY:
// It never gets to this point
// Decrease windows count
this->WindowsCount--;
PostQuitMessage(0);
break;
break;
default:
return DefWindowProc(hWnd, msg, wParam, lParam);
}
return 0;
}
And now a class which holds the static WNDPROC, which is assigned at creation
class MyApp
{
public:
static HINSTANCE Instance;
static int WindowsCount;
MyApp();
static LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
};
and implementation
LRESULT CALLBACK MyApp::WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
// Window object
MyWindow* myWindow = NULL;
if (msg == WM_CREATE) {
myWindow = reinterpret_cast<MyWindow *>(((LPCREATESTRUCT)lParam)->lpCreateParams);
SetWindowLongPtr(hWnd, GWLP_USERDATA, (LONG_PTR)myWindow);
}
else {
myWindow = reinterpret_cast<MyWindow *>(GetWindowLongPtr(hWnd, GWLP_USERDATA));
}
// If window not identified, identify now
if (myWindow) {
return myWindow->WndProc(hWnd, msg, wParam, lParam);
}
// Call window object's processor
return DefWindowProc(hWnd, msg, wParam, lParam);
}
The WM_CLOSE message is not caught either. I really do not understand why these messages are not passed on

Answer 1

You are setting the lpParam parameter of CreateWindowEx() to nullptr, so myWindow is always nullptr in MyApp::WndProc(), thus MyWindow::WndProc() is never called. You need to pass this instead of nullptr.
You are also not doing any error checking to make sure RegisterClassExW() and CreateWindowEx() succeed before calling ShowWindow()/UpdateWindow().
Also, consider using SetWindowSubclass() instead of (Get|Set)WindowLongPtr(GWLP_USERDATA). See Subclassing Controls on MSDN, and Raymond Chen's blog article on Safer Subclassing.