window fails to initiate when specifying a custom class name registered with RegisterClass to Create-CodePudding

I'm creating a window that's supposed to contain buttons. When I create the first window (the container) I use a WNDCLASS to specify a WindowProc callback function to lpfnWndProc and it works as intended. When I do it the second time with a window, specifying a callback used to detect when the button is clicked, it doesn't work; the CreateWindowEx call there returns NULL (comment below shows where).

When I don't create WNDCLAS wB below and specify some other valid lpClassName to CreateWindowEx instead, such as Button it works fine.

code used

#pragma comment(linker, "/entry:wWinMainCRTStartup")

#include <windows.h>

#include <iostream>

HWND button;

LRESULT CALLBACK ButtonWindowProc(HWND hwnd, UINT uMsg, WPARAM wParam,
                                  LPARAM lParam);
LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE, PWSTR pCmdLine,
                    int nCmdShow) {
  WNDCLASS wc = {};

  wc.lpfnWndProc = WindowProc;
  wc.hInstance = hInstance;
  wc.lpszClassName = L"textedit";

  RegisterClass(&wc);

  HWND hwnd = CreateWindowEx(
      0, wc.lpszClassName, L"textedit", WS_OVERLAPPEDWINDOW,

      CW_USEDEFAULT, CW_USEDEFAULT, 340, 240, NULL, NULL, hInstance, NULL);
  if (hwnd == NULL) {
    return 0;
  }

  HWND hWndEdit = CreateWindowEx(WS_EX_CONTROLPARENT, L"Edit", L"id here",
                                 WS_BORDER | WS_CHILD | WS_VISIBLE, 94, 20, 140,
                                 40, hwnd, NULL, NULL, NULL);
 
  // if I leave wcB unused/remove it and
  // specify L"Button" as the lpClassName to CreateWindowEx below, the button displays

  WNDCLASS wcB = {};

  wcB.lpfnWndProc = ButtonWindowProc;
  wcB.hInstance = hInstance;
  wcB.lpszClassName = L"modify";

  RegisterClass(&wcB);

  ShowWindow(hwnd, nCmdShow);
  // doing the exact same thing I did when creating the first window
  // but it fails to create the window

  HWND hButton =
      CreateWindowEx(0L, L"modify", L"modify", BS_FLAT | WS_VISIBLE | WS_CHILD,
                      94, 70, 140, 50, hwnd, NULL, hInstance, NULL);
  ShowWindow(hButton, nCmdShow);

  // here hButton is NULL     <----------------------

  if (hButton == NULL) {
    return 0;
  }
  MSG msg = {};
  while (GetMessage(&msg, NULL, 0, 0)) {
    TranslateMessage(&msg);
    DispatchMessage(&msg);
  }

  return 0;
}

LRESULT CALLBACK ButtonWindowProc(HWND hwnd, UINT uMsg, WPARAM wParam,
                                  LPARAM lParam) {
  switch (uMsg) {
    case WM_DESTROY:
      PostQuitMessage(0);
      return 0;

    case BN_CLICKED:
         std::cout << "clicked";
    case WM_PAINT:
      PAINTSTRUCT ps;
      HDC hdc = BeginPaint(hwnd, &ps);
      FillRect(hdc, &ps.rcPaint, (HBRUSH)(COLOR_WINDOW   1));
      EndPaint(hwnd, &ps);

      return 0;
  }

  return 0;
  return DefWindowProc(hwnd, uMsg, wParam, lParam);
};

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam,
                            LPARAM lParam) {
  switch (uMsg) {
    case WM_DESTROY:
      PostQuitMessage(0);
      return 0;

    case WM_PAINT:
      PAINTSTRUCT ps;
      HDC hdc = BeginPaint(hwnd, &ps);
      FillRect(hdc, &ps.rcPaint, (HBRUSH)(COLOR_WINDOW   1));
      EndPaint(hwnd, &ps);

      return 0;
  }

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

GetLastError() returns 1400, but I don't understand how the handle hwnd could possible be invalid because as I mentioned before, when I just change the lpClassName I pass to CreateWindowEx, it works without errors.

I would appreciate any help in finding out why the window (the HWND of which is hButton) does not initiate, and possible workarounds.

CodePudding user response：

The solution to the problem in the title was solved by the comment by Igor Tandetnik:

ButtonWindowProc returns 0 for all messages it doesn't handle, and doesn't pass them to DefWindowProc. In particular, it returns 0 in response to WM_NCCREATE, which is a signal that the window creation has failed. You probably didn't mean to put return 0; right before return DefWindowProc(...);

After fixing that, the window was created but was invisible. To fix that I used FillRect without (HBRUSH)(COLOR_WINDOW 1)

 SetDCBrushColor(hdc, bkcolor);
 SetBkColor(hdc, RGB(187, 189, 189));
 FillRect(hdc, &ps.rcPaint, (HBRUSH)GetStockObject(DC_BRUSH));

to fix the cursor not being a pointer, I set the hCursor.

wcB.hCursor = LoadCursor(NULL, IDC_HAND);

Lastly, to detect left mouse button clicks I checked for the WM_LBUTTONDOWN message.