WinAPI - button cannot be clicked - c++

Question

I want to make a panel, which groups buttons by itself:
HWND my_panel = CreateWindow(
"STATIC",
"",
WS_VISIBLE | WS_CHILD | WS_BORDER,
30,
100,
300,
300,
main_window, // main dialog
NULL,
( HINSTANCE ) GetWindowLong( main_window, GWL_HINSTANCE ),
NULL
);
Then I add a button to this panel:
HWND button_in_a_group = CreateWindow(
"BUTTON",
"Hello world",
WS_VISIBLE | WS_CHILD | BS_DEFPUSHBUTTON,
20,
20,
50,
50,
my_panel, // as a child for above
NULL,
( HINSTANCE ) GetWindowLong( main_window, GWL_HINSTANCE ),
NULL
);
When I click the button, it doesn't send a WM_COMMAND but WM_PARENTNOTIFY to callback function. Then, if I press Enter, it works - WM_COMMAND is sent by the button.
How to enable mouse click on nested button, and why nested windows doesn't work as expected?

Answer 1

Messages are sent to parent window. In this case the static windows is the button's parent. So the main window is not receiving button messages, except WM_PARENTNOTIFY.
You can subclass the static window:
SetWindowSubclass(my_panel, ChildProc, 0, 0);
Define a ChildProc to catch the button messages. See also Subclassing Controls
The button also requires an identifier as follows:
CreateWindow("BUTTON", "Hello world", ... my_panel, HMENU(BUTTON_ID) ...);
WM_COMMAND message is sent to ChildProc when button is clicked. The BN_CLICKED notification carries BUTTON_ID
Note, SetWindowSubclass needs additional header and library:
#include <CommCtrl.h>
#pragma comment(lib, "Comctl32.lib") //Visual Studio option for adding libraries
...
LRESULT CALLBACK ChildProc(HWND hwnd, UINT msg,
WPARAM wParam, LPARAM lParam, UINT_PTR, DWORD_PTR)
{
switch(msg) {
case WM_COMMAND:
switch(LOWORD(wParam)) {
case BUTTON_ID:
MessageBox(0, "hello world", 0, 0);
break;
}
break;
case WM_NCDESTROY:
RemoveWindowSubclass(hwnd, ChildProc, 0);
break;
}
return DefSubclassProc(hwnd, msg, wParam, lParam);
}