Missing resources in QT Stylesheets

Question

I am using stylesheets in QT to skin several buttons with images from the QT resource system:

QFrame#DialogButtonTitle_SaveAsNew
{
  background-image: url(images:DialogButtonTitle_SaveAsNew.png);
}

This works great, but I would really like to write a warning to our logs if the image file could not be found (and the button is thus naked). Any way to catch such errors?

Answer 1

It's possible that Qt will call one of their message functions when something like this happens (although I don't know for sure). If it does, you could install a message handler function and append some or all of the messages to your log file. There is some information about doing so in the documentation for qInstallMsgHandler.

Answer 2

I believe you can do it like this:

• Read about the QAbstractFileEngine and QAbstractFileEngineHandler classes.
• Extend Qt's own implementation, QFSFileEngine. I believe it also handles the ":" namespace.
• Reimplement the QAbstractFileEngine::open() method.
• Register your engine using a custom QAbstractFileEngineHandler. The create() method should check the file name to see if it is being read from a resource file.

Haven't tested, but I think it should work. Code:

bool MyEngine::open(QIODevice::OpenMode mode)
{
    bool r = QFSFileEngine::open(mode);
    if (!r) {
        qWarning() << "Failed to open" << fileName();
    }
    return r;
}

QAbstractFileEngine *MyEngineHandler::create(const QString &fileName) const
{
     return fileName.startsWith("images:") ? new MyEngine(fileName) : 0;
}

Edit.

This will not work. The resource file system, “:”, is handled by a private file engine called QResourceFileEngine, not by QFSFileEngine.