BM_GETCHECK not working - c++

Question

I have code like this :
In WM_CREATE
hCheckBox = CreateWindowEx(0,"Button","Random text", WS_CHILD | WS_VISIBLE | WS_CLIPSIBLINGS| BS_AUTOCHECKBOX | BS_TEXT | WS_GROUP | WS_TABSTOP,150,323,300,20,hwnd,0,hInstance,0) ;
In WM_COMMAND
if ( SendMessage( hCheckBox , BM_GETCHECK, (WPARAM) NULL, (LPARAM) NULL ) == BST_CHECKED )
MessageBox( 0, "Working", "Msg", 0 );
Doesn't matter if the checkbox is checked or not, it never return BST_CHECKED.
Trying to make it work for the last 2 hours :(

Answer 1

It is not entirely apparent whether hCheckBox is a local automatic variable. If so, I can assure you it is not holding its value from the time the CreateWindow fires until the time the WM_COMMAND message is received. Use this instead:
LRESULT chk = SendDlgItemMessage(hDlg, IDC_CHECKBOX_CTRL_ID, BM_GETCHECK, 0, 0);
Where hDlg is your dialog or main window handle, and IDC_CHECKBOX_CTRL_ID is the control ID. To that, you need to specify the control id as a non-zero value for the HMENU parameter to your create-call:
hCheckBox = CreateWindowEx(0,"Button","Random text", WS_CHILD | WS_VISIBLE |
WS_CLIPSIBLINGS| BS_AUTOCHECKBOX | BS_TEXT | WS_GROUP |
WS_TABSTOP,150,323,300,20,hwnd, IDC_CHECKBOX_CTRL_ID, hInstance,0);
And in case it wasn't obvious. Define IDC_CHECKBOX_CTRL_ID as a non-zero integer.
EDIT
Assuming the control is setup correctly, you should be able to handle the WM_COMMAND for this checkbox as follows in your WndProc
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
int wmId, wmEvent;
switch (message)
{
case WM_CREATE:
CreateWindowExA(0,"Button","Random text", WS_CHILD | WS_VISIBLE |
WS_CLIPSIBLINGS| BS_AUTOCHECKBOX | BS_TEXT | WS_GROUP |
WS_TABSTOP,100,100,300,48, hWnd, (HMENU)IDC_CHECKBOX_CTRL_ID, hInst, 0);
break;
case WM_COMMAND:
wmId = LOWORD(wParam);
wmEvent = HIWORD(wParam);
// Parse the menu selections:
if (wmId == IDC_CHECKBOX_CTRL_ID)
{
if (wmEvent == BN_CLICKED)
{
LRESULT chkState = SendMessage((HWND)lParam, BM_GETCHECK, 0, 0);
if (chkState == BST_CHECKED)
MessageBoxA(hWnd, "Checkbox is checked!", "CheckBox", MB_OK);
}
break;
};
// fall-thru intentional
default:
return DefWindowProc(hWnd, message, wParam, lParam);
};
return 0;
}
I just slammed this into a stock generic WIN32 app with a blank window. the results are in the image below: