Stacked dock widgets tab bars not consistent

  • Hello! I am relatively new to Qt, and have been pulling my hair out trying to solve this issue. I am working on a theme for the open source project OBS, which just updated to allow dock widgets for many of the main UI elements.

    However, when stacking two dock widgets together, the QTabBar is near impossible to style correctly with a QSS file, and the overall behavior is extremely inconsistent. For example, the biggest issue I'm having is that the separator line (I'm not even really sure what to call this specific element) is present when two widgets are newly stacked, as shown here:

    New stack

    But when the program is restarted, this line is now gone, and the entire object looks different (presumably because this line is adding 1px of height to the QTabBar itsel:

    Old stack

    So, the question I have is, in the context of a stacked dock widget, what is that line element called and how can I select it/remove/change it with QSS or otherwise? QSS would be preferred as that will be the minimum amount of changes needed. I have searched around and found quite a few people having this same issue with the dock widget tab bar and how it does not behave like a normal QTabBar. Thanks in advance for any advice or help you can provide.

    For reference, here is the QSS I'm working with as it relates to the QTabBar:

  • Lifetime Qt Champion

    Hi and welcome to devnet,

    Can you also provide a minimal sample code that shows the problem once the style sheet is applied ?

  • @SGaist Unfortunately, I don't think I will be able to. As I mentioned, I'm very new to Qt and I don't know how to generate a sample application (I know next to nothing about C/C++, I'm more of a web guy).

    I will see if I can find some simple sample applications, however, and try to replicate it there.

  • Ok, I've managed to create a reduced test case (using the Dock Widgets example app that ships with Qt) to replicate this issue.

    What constitutes "minimal sample code" that you need to see here? Here's what happens in the example:

    Before restart:

    After restart:

    You can see that the line is 1px smaller after relaunching the test app.

  • Lifetime Qt Champion

    If the code is small you can post it here.

  • @SGaist I still don't understand what specifically you're asking for, so here's the entire application:

  • Any updates? Do I need to provide anything further for this to be looked at?

  • Lifetime Qt Champion

    That might be specific to Windows, It doesn't seem to happen on macOS.

    On a side note, your gist is missing a .pro and .qrc file and the Q_INIT_RESOURCE is not needed and done too late.

  • So no other suggestions or ideas? I really just need to understand if this is a Qt problem, or a problem with my .qss file.

    I can provide the missing files when I get time, but I don't think they're relevant to this issue and if I remember correctly, they were pretty much blank anyway.

    As for the code itself, this is the example code that ships with Qt, the only modification I did was to apply my theme, so I'm not sure what you mean by "not needed and done too late" there. I can try removing it and see if it makes a difference, however.

  • Bump, still looking for an answer on this. Thanks!

  • Lifetime Qt Champion

    In between did you update Qt ? 5.10 is just around the corner with the Beta 4 that was just released.

  • I am currently building against 5.9.1, and the issue is still present. I was building against 5.7.0 before.

    I am very reluctant to update to the latest for compatibility reasons.

  • Lifetime Qt Champion

    Why 5.9.1 ? 5.9.3 got released and 5.10 is in RC.

  • 5.9.1 is what I have been testing against. I've installed 5.10 and the same issue occurs.

    5.7.0 is what the application is currently shipping with, as mentioned due to compatibility concerns. We are looking to update Qt to a newer version in the near future that includes VS2017 support, but we have many different (and older) versions of macOS and Linux that must remain supported.

  • Lifetime Qt Champion


    you stylesheet looked so nice ( even without right icons)
    I tested it and could reproduce it on Linux and Windows.
    (after restore state/ running second time, it would loose a pixel)

    If i float and redocked/tabbed them again, it would draw as expected.

    Using trial and error and found out that if i remove
    alt text

    I could no longer reproduce it.

    had same issue
    and also contained

        qproperty-drawBase: 0;
        border-radius: 3px;

    So my conclusion is that the line
    qproperty-drawBase: 0;
    Is not working 100% and start searching for that and found

    I tried

    QList<QDockWidget *> dockWidgets = findChildren<QDockWidget *>();
        for (int var = 0; var < dockWidgets.size(); var++) {

    But as far as I can test.
    Using qproperty-drawBase: 0; is a no go with Docks and tabs.

    If i do ( with qproperty-drawBase: 1; in stylesheet)
    (using the menu New Letter)

      for (int var = 0; var < dockWidgets.size(); var++) {
        if (dockWidgets[var]->drawBase())

    after restorestate
    i get the the missing line syndrom instantly.
    alt text

    I assume it has something to do with its a property and not a stylesheet tag but
    i have no future info but other qproperty- uses have issues too.


  • Lifetime Qt Champion

    Nice catch !

  • @mrjj said in Stacked dock widgets tab bars not consistent:




    Thank you so much for this. That was definitely it. I found the same conflicting reports that using a property in QSS like that should work (and it does seem to sometimes work), but that was definitely the issue. Tested removing the property line and now everything is working consistently.

    I can't figure out another way of styling that divider line in QSS, but I can at least work around it now that there's some level of consistency. Thank you, again, for pointing me in the right direction!

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