Taskbars; 'Cannot create top level child window'

This is a discussion on Taskbars; 'Cannot create top level child window' within the Windows Programming forums, part of the Platform Specific Boards category; My current problem involves taskbars. I've added libcomctl32.a to the linker stuff in my project options in Dev C++ and ...

  1. #1
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    Taskbars; 'Cannot create top level child window'

    My current problem involves taskbars. I've added libcomctl32.a to the linker stuff in my project options in Dev C++ and included commctrl.h and it compiles OK. I have the code in my WM_CREATE for the main window. HWND hStatus is outside of it.
    Code:
            InitCommonControls();
    
    	hStatus = CreateWindowEx(0, STATUSCLASSNAME, NULL,
            WS_CHILD | WS_VISIBLE | SBARS_SIZEGRIP, 0, 40, 0, 40,
            g_hWnd, (HMENU)ID_STATUS, GetModuleHandle(NULL), NULL);
    
            int statwidths[] = {100, -1};
    
        	SendMessage(hStatus, SB_SETPARTS, 2, (LPARAM)statwidths);
        	SendMessage(hStatus, SB_SETTEXT, 0, (LPARAM)"Hi there :)");
    This is from the winprog status bar tutorial. Problem is, CreateWindowEx returns NULL and the error code is 1406 which apparently is 'Cannot create top level child window'. what? MSDN says something about it, but it is very brief and it's not from the developer perspective.

    A child window is 'any window that is not a top level window', but I can't see what's going on in the above that makes it like that. I read other posts that said the code there works fine. Any ideas?

  2. #2
    Registered User Queatrix's Avatar
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    Maybe you made a mistake similar to the one in your other post?
    The reason I say that, is because that code compiles and runs fine for me.

  3. #3
    Cat without Hat CornedBee's Avatar
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    Let me guess. You create the main window like this:
    Code:
    g_hWnd = CreateWindowEx(...);
    The effect of this is: g_hWnd doesn't get a value until CreateWindowEx returns. Which is after WM_CREATE is dispatched to the new window. (The reason for that is, if WM_CREATE returns FALSE, window creation fails.)

    So the g_hWnd you use in WM_CREATE is still NULL - to the system, it looks like you want the window to be top-level, which contradicts you passing WS_CHILD.

    The solution is to never use global window handles in the WndProc; always use the HWND passed to the procedure.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

  4. #4
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    Thanks, now the status bar appears just fine. I changed the application to use 1 big parent window and child windows for the status bar and scroll area. Now I'd like to know if there's a GetSytemMetric-esque function / message for the status bars so I can figure out sizes for the scrolling child window when resizing and such. MSDN states the font determines the height but ...

    -I can't find a function that returns the height of the font.
    -There's still the rest of the area that isn't taken up by text.

    I first figured that the window size you create the status bar with determines it's height but it turns out it's not that easy.

  5. #5
    Cat without Hat CornedBee's Avatar
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    I can't find a function that returns the height of the font.
    GetFontMetrics. Or just GetFont/GetObject, the LOGFONT structure might contain the necessary stuff.

    There's still the rest of the area that isn't taken up by text.
    That ought to be a simple calculation based on the font size.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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