SetViewportMargins() and “locked” rows and columns

  • Hello,
    the documentation of void QAbstractScrollArea::setViewportMargins(int left, int top, int right, int bottom) says:

    Sets the margins around the scrolling area to left, top, right and bottom. This is useful for applications such as spreadsheets with "locked" rows and columns. The marginal space is is left blank; put widgets in the unused area.
    Note that this function is frequently called by QTreeView and QTableView, so margins must be implemented by QAbstractScrollArea subclasses. Also, if the subclasses are to be used in item views, they should not call this function.

    First of all, I got confused with description itself. The function is not virtual so it is not the case when I should re-implement it to supply my margins. If I should call it than when, at what points? And if QTreeView is calling it internally with its own values than how our calls will cooperate? Looking at Qt sources I have found that QTreeView::updateGeometries() does call it with parameters (essentially) 0, headerHeight, 0, 0. So should I re-implement updateGeometries()?

    Googling further I found that other people call setViewportMargins() from overridden resizeEvent(). So I also did so and this works BUT:

    #. I am wondering how this technique co-exist with internal QTreeView::updateGeometries() that calls setViewportMargins() with essentially hard-coded parameters (only headerHeight is changed to 0 if header is hidden)?
    #. Although it works the "unused area" appears above header. But to implement "locked" rows mentioned by documentation one needs this area to be under header

    I have got unused area below header by overriding updateGeometries() and moving header() to the top (after calling QTreeView::updateGeometries();). But I am not sure that this is right thing to do.

    So my question is:
    What way to implement "locked" rows is meant by setViewportMargins() documentation and how should they actually be implemented?

    Thank you

    P.S. Note that I am aware about another way to implement frozen rows (or columns) - "Frozen Column Example": But this is not exactly what I need because this technique hides first row(column) of main table(tree) widget and shows it in overlay (static) widget. In my case I need a different info in the area below header and main widget should be actually moved down to show all rows

  • @mvidelgauz Hi, I have exactly the same problem and I couldn't find any answer to it on the web. Did you resolve your issue somehow? Would be very grateful for help.

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