使用CreateWindow创建MDI子窗口

Question

this works

mcs.szTitle = L"untitled";
mcs.szClass = childClassName;
mcs.hOwner  = GetModuleHandle(NULL);
mcs.x = mcs.cx = CW_USEDEFAULT;
mcs.y = mcs.cy = CW_USEDEFAULT;
mcs.style = WS_HSCROLL;
hChild = (HWND)SendMessage(hMDIClient, WM_MDICREATE, 0, (LONG)&mcs);

but I can't send it a pointer to the object that has the WndProc I'd like to use (see here for wrapping up WndProc in classes) like this

hChild = CreateWindow(childClassName, L"", WS_VISIBLE, CW_USEDEFAULT, CW_USEDEFAULT, 400, 250, hMDIClient, NULL, GetModuleHandle(NULL), this);

However doing it like that will cause an error with the windo, there will be no zlose, no minimise, no maximise, I can't resize it, and if I create another mdi child window, the previous one will become deselectable.

Is it possible to use either SendMessage or CreateWindow, pass a this pointer and still create a working MDI Child window?

Answer 1

I solved it by doing this

hChild = CreateMDIWindow(childClassName, L"", WS_EX_WINDOWEDGE, 49, 50, 51, 52, hMDIClient, GetModuleHandle(NULL), (LPARAM)this);

and then in the static WndProc

LRESULT CALLBACK CWindowHandler::MsgRouter(HWND hwnd, UINT message,
                                            WPARAM wparam, LPARAM lparam)
{
    CREATESTRUCT* wnd = 0;
    MDICREATESTRUCT* mdiStruct = 0;
    CMDIChildWindowBase* wndBase;

    if(message == WM_NCCREATE)
    {
        wnd = (CREATESTRUCT*)(lparam);
        mdiStruct = (MDICREATESTRUCT*)wnd->lpCreateParams;
        wndBase = (CMDIChildWindowBase*)mdiStruct->lParam;
        SetWindowLongPtr(hwnd, GWLP_USERDATA, reinterpret_cast<LONG_PTR>(wndBase));

        // save window handle
        wndBase->SetHWND(hwnd);
    }
    else
        wndBase = reinterpret_cast<CMDIChildWindowBase *>(::GetWindowLong(hwnd, GWL_USERDATA));

    // call the windows message handler
    if(wndBase)
        return wndBase->WndProcs(message, wparam, lparam);
    return DefWindowProc(hwnd, message, wparam, lparam);
}

so when creating an MDIChild, lparam in WndProc will be a pointer to a CREATESTRUCT, whose lpCreateParams will be a MIDICREATESTRUCT, whose lParam will be the pointer to your object.

phew.

Answer 2

When you pass the MDICREATESTRUCT to WM_MDICREATE , you can provide the object pointer in MDICREATESTRUCT.lParam field:

mcs.szTitle = L"untitled";
mcs.szClass = childClassName;
mcs.hOwner  = GetModuleHandle(NULL);
mcs.x = mcs.cx = CW_USEDEFAULT;
mcs.y = mcs.cy = CW_USEDEFAULT;
mcs.style = WS_HSCROLL;
mcs.lParam = (LPARAM) this; // <-- here

hChild = (HWND) SendMessage(hMDIClient, WM_MDICREATE, 0, (LPARAM)&mcs);