Linux - Support system's theme change

  • Hi,

    I have just noticed that though my application works as I would expect on Linux (Ubuntu 11.04), if I change my system's theme, then my application doesn't fully handle the change. The window border decoration will respect the theme, but the menus, dialog buttons, etc. won't.

    I have just checked with the Qt (4.7.3) demos (which I manually built on my Ubuntu 11.04 box) and it's the same. They, in fact, use the same (default?) theme as my application. However, everything works as I would expect using Qt Creator 2.2.1.

    So, what is the difference between my application / the Qt demos and Qt Creator? How do I go about ensuring that my application respects the system's theme?

    Cheers, Alan.

    P.S.: I have just checked on Windows and Mac OS X, and as far as I can tell everything works as expected, i.e. my application handles changes in the system's theme without any problem.

  • What happens if you set the style of your program in code?
    What style are you trying to use?

  • If I programmatically set a style, e.g.
    @app->setStyle(new QPlastiqueStyle);@
    then the style is properly set, but it obviously doesn't respond to any change to the system's theme, and is therefore not what I want.

    In fact, I don't use and don't want to use any particular style. I just want my application to use the 'default' system style and respond to any change to it. Nothing more nothing less.

  • The problem is, that your app runs on gnome and this is gtk and not Qt. If you use KDE, your app will use the system theme!

  • I've used kubuntu 10.10 in the past and there it's ok. But that's kde.

    Are you sure about that Scylla?
    It seems strange to me.

    A workaround could be to get the system style in code and set it like you did.

  • Here it works as expected (Kubuntu 1010). If you don't use a hard coded style, it should work on KDE.

  • You need to have a GTK style engine in Qt, so that Qt will use GTK styling by default.

    EDIT: Okay, that link is outdated. But anyway, that piece of code allows to use GTK styles in Qt, I don’t know where is instructions to use it.

  • For what it is worth, I quickly installed Kubuntu 11.04, and ran my application on it, and its look didn't match that of the KDE theme. Then again, I built my application on Ubuntu 11.04 and copied it over to my Kubuntu system, so it might explain...? (Note: I don't use any hard-coded style and, in fact, don't want to have to do that at all, since my application may end up being use on different flavours of Linux.)

    Eddy: what do you mean by "get the system style in code"?

    Smar: I have seen that Qt has QGtkStyle class, but on my Ubuntu box, QT_NO_STYLE_GTK is defined and therefore QGtkStyle is not available. Then again, as I mentioned before, I don't want to have to use styles. I would just hope that things would somehow work... :)

  • Hi Alan,

    There is an example called stylesheet that uses the solution I talked about.

    @QString defaultStyle = QApplication::style()->metaObject()->className();@

    have a look in the StyleSheetEditor constructor.

    About Ubuntu 11.04 : I read that they are leaving gtk. Maybe this has something to do with it? Since prior versions of ubuntu didn't have this problem.

  • Thanks Eddy. I just had a quick look and for my application under Ubuntu 11.04, the following code:

    @QRegExp regExp(".(.*)\+?Style");
    QString defaultStyle = QApplication::style()->metaObject()->className();

    qDebug() << "BEFORE:" << defaultStyle;

    if (regExp.exactMatch(defaultStyle))
    defaultStyle = regExp.cap(1);

    qDebug() << "AFTER:" << defaultStyle;@


    bq. BEFORE: "QCleanlooksStyle"
    AFTER: "Cleanlooks"

    This is already the style that my application uses, so I am not sure it helps...?

  • Did you try to set it in code using that string eventually? I suppose you did.
    The reason why I ask is that you told us before that setting it using code went well.
    If it's not, there must be a problem with the them I suppose on your system.

  • Well, I did try indeed (using app->setStyle(new QCleanlookStyle), even though app->style() would return QCleanLookStyle before I set the 'new' style.

    Otherwise, I did say that hard setting the style worked in the sense that the style gets applied, but I also said that if I change the theme, then my application doesn't respond to the change.

    As I also said, the Qt examples behave the same as my application (i.e. don't respond to a change in the theme) while Qt Creator works as expected (i.e. responds to a change in the theme).

  • Sorry it couldn't help you out. It was worth trying I guess.

  • No worries, and yes always worth trying. I guess that if I was to study Qt Creator's source code carefully, then I would find out how they do it...

  • Sounds like a good idea. And you could learn other usefull things.

    Keep us posted.

  • Oh, I already have from Qt Creator's source code. :) It's just that I am still struggling about the overall structure of the source code, so I tend to use it as a last resource.

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