Native QFileDialog position under Win32

[no_ghost]

Qt documentation says:

"Note that on Windows the dialog will spin a blocking modal event loop that will not dispatch any QTimers, and if parent is not 0 then it will position the dialog just under the parent's title bar."

Not in the center of the parent window, as one expecting.

But WinAPI provides a very simple way to define native file dialog's positions. In few words - you have to assign a hook function pointer in OPENFILENAME structure and position dialog properly in that function.

This function creates correct OPENFILENAME (don't forget to make similar changes in qt_win_make_OFNA function)

static OPENFILENAME* qt_win_make_OFN(QWidget *parent,
                                     const QString& initialSelection,
                                     const QString& initialDirectory,
                                     const QString& title,
                                     const QString& filters,
                                     QFileDialog::FileMode mode,
				     QFileDialog::Options options)
{
 
    // ....
    OPENFILENAME* ofn = new OPENFILENAME;
    memset(ofn, 0, sizeof(OPENFILENAME));
 
    // ....
    ofn->lpfnHook = qt_win_ofn_hook; // custom hook
    ofn->lCustData = (LPARAM)parent; // parent of dialog window
    ofn->Flags = (OFN_NOCHANGEDIR | OFN_HIDEREADONLY | OFN_EXPLORER | OFN_ENABLEHOOK); // OFN_ENABLEHOOK enables ofn hook fields
    // ....
}

static OPENFILENAME* qt_win_make_OFN(QWidget *parent,
                                     const QString& initialSelection,
                                     const QString& initialDirectory,
                                     const QString& title,
                                     const QString& filters,
                                     QFileDialog::FileMode mode,
				     QFileDialog::Options options)
{

    // ....
    OPENFILENAME* ofn = new OPENFILENAME;
    memset(ofn, 0, sizeof(OPENFILENAME));

    // ....
    ofn->lpfnHook = qt_win_ofn_hook; // custom hook
    ofn->lCustData = (LPARAM)parent; // parent of dialog window
    ofn->Flags = (OFN_NOCHANGEDIR | OFN_HIDEREADONLY | OFN_EXPLORER | OFN_ENABLEHOOK); // OFN_ENABLEHOOK enables ofn hook fields
    // ....
}

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And this is a hook function:

UINT_PTR CALLBACK qt_win_ofn_hook(HWND hdlg, UINT uiMsg, WPARAM wParam, LPARAM lParam)
{
    // process initialization message
    if(uiMsg == WM_INITDIALOG)
    {
        OPENFILENAME* ofn;
        QWidget* parent;
 
        HWND frame_dlg;
        RECT frame_rect;
 
        QRect parent_rect;
 
        int dlg_left;
        int dlg_top;
 
        // this should work even if lParam points to OPENFILENAMEA
        ofn = (OPENFILENAME*)lParam; // ofn goes to lparam (as MSDN says)
        parent = (QWidget*)ofn->lCustData; // custom data filled in ofn
 
        if(parent == 0)
        {
            // using desktop if no parent window
            parent_rect = QApplication::desktop()->geometry();
        }
        else
        {
            // getting parent rect
            QPoint parent_topleft;
 
            parent_topleft = parent->mapToGlobal(QPoint(0, 0));
            parent_rect = QRect(parent_topleft, parent->size());
        }
 
        frame_dlg = GetParent(hdlg); // file dialog handle
        GetWindowRect(frame_dlg, &frame_rect); // file dialog frame rect
 
        // compute left and top of final rect
        dlg_left = (parent_rect.left() + parent_rect.right()) / 2 - 
            (frame_rect.right - frame_rect.left) / 2;
        dlg_top = (parent_rect.top() + parent_rect.bottom()) / 2 - 
            (frame_rect.bottom - frame_rect.top) / 2;
 
        // position file dialog
        SetWindowPos(frame_dlg, 0, dlg_left, dlg_top, 0, 0, SWP_NOSIZE);
    }
 
    return FALSE;
}

UINT_PTR CALLBACK qt_win_ofn_hook(HWND hdlg, UINT uiMsg, WPARAM wParam, LPARAM lParam)
{
    // process initialization message
    if(uiMsg == WM_INITDIALOG)
    {
        OPENFILENAME* ofn;
        QWidget* parent;

        HWND frame_dlg;
        RECT frame_rect;

        QRect parent_rect;

        int dlg_left;
        int dlg_top;

        // this should work even if lParam points to OPENFILENAMEA
        ofn = (OPENFILENAME*)lParam; // ofn goes to lparam (as MSDN says)
        parent = (QWidget*)ofn->lCustData; // custom data filled in ofn

        if(parent == 0)
        {
            // using desktop if no parent window
            parent_rect = QApplication::desktop()->geometry();
        }
        else
        {
            // getting parent rect
            QPoint parent_topleft;

            parent_topleft = parent->mapToGlobal(QPoint(0, 0));
            parent_rect = QRect(parent_topleft, parent->size());
        }

        frame_dlg = GetParent(hdlg); // file dialog handle
        GetWindowRect(frame_dlg, &frame_rect); // file dialog frame rect

        // compute left and top of final rect
        dlg_left = (parent_rect.left() + parent_rect.right()) / 2 - 
            (frame_rect.right - frame_rect.left) / 2;
        dlg_top = (parent_rect.top() + parent_rect.bottom()) / 2 - 
            (frame_rect.bottom - frame_rect.top) / 2;

        // position file dialog
        SetWindowPos(frame_dlg, 0, dlg_left, dlg_top, 0, 0, SWP_NOSIZE);
    }

    return FALSE;
}

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Full qfiledialog_win.cpp file is in the attachments.

Hope it will help. Or may be, in one beautiful day, it will be commited to the main repository.