DialogBox not drawing the dialog correctly - winapi

Question

So I have the following dialogbox template which I saved in a .rc file:
DIALOG_TEST DIALOG 0, 0, 186, 95
STYLE DS_3DLOOK | DS_CENTER | DS_MODALFRAME | DS_SHELLFONT | WS_CAPTION | WS_VISIBLE | WS_POPUP | WS_SYSMENU
CAPTION "Dialog"
FONT 8, "Ms Shell Dlg"
{
PUSHBUTTON "Cancel", IDD_CAN, 129, 24, 50, 14, 0, WS_EX_LEFT
DEFPUSHBUTTON "OK", IDD_OK, 129, 7, 50, 14, 0, WS_EX_LEFT
}
which I call using DialogBox in the following way:
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
HWND button;
switch (message) /* handle the messages */
{
case WM_CREATE:
button = CreateWindowEx(WS_EX_CLIENTEDGE, "BUTTON",
"Test",
WS_VISIBLE | WS_CHILD | WS_BORDER,
200, 40, 200, 30,
hwnd, (HMENU) 1, NULL, NULL);
break;
case WM_COMMAND:
switch(LOWORD(wParam))
{
case 1:
DialogBox(GetModuleHandle(NULL), TEXT("DIALOG_TEST"),
hwnd, AboutDlgProc);
break;
}
break;
case WM_DESTROY:
PostQuitMessage (0); /* send a WM_QUIT to the message queue */
break;
default: /* for messages that we don't deal with */
return DefWindowProc (hwnd, message, wParam, lParam);
}
return 0;
}
All works fine except that for some reason the window is not being drawn correctly:
it's like the dialogbox is being drawn twice, what am I doing wrong?
As for the Window Procedure for the dialogbox, the only thing it does is close the window when the "Cancel" is pressed.
BOOL CALLBACK AboutDlgProc(HWND hDlg, UINT message,
WPARAM wParam, LPARAM lParam)
{
switch (message)
{
case WM_COMMAND:
switch(HIWORD(wParam))
{
case BN_CLICKED:
switch (LOWORD (wParam))
{
case IDD_CAN:
EndDialog(hDlg, TRUE);
return TRUE ;
}
break;
}
break;
}
}

Answer 1

A button can send more than one kind of notification in a WM_COMMAND message, so if you want to create the dialog box only when the button is clicked you need to check to make sure that the notification code (in HIWORD(wParam)) is BN_CLICKED. See WM_COMMAND documentation.