How to use Qt plugins?

[AndrzejB]

I start creating BPG image plugin. I see https://github.com/FreeSlave/qt-sprite-image-plugin as example.

1. How use plugins? For example in my ImageViewer, is possible dynamic register ?
2. How register in system , for GwenView? only in KDE?
3. What about versions Qt main program and version Qt used to create plugins ? May be different?

[AndrzejB]

Now, is Qt5 error in

Q_EXPORT_STATIC_PLUGIN(ArgbPlugin)
Q_EXPORT_PLUGIN2(argb, ArgbPlugin)

Now I found solution:
https://stackoverflow.com/questions/22394477/how-to-create-plugins-qt-5-2-0

Where must be folder imageformats? What is QT_INSTALL_PLUGINS ?
How call install, how migrate from .pro to cmake?
Solved where folder:
https://www.qtcentre.org/threads/46927-Location-of-imageformats-directory

[Christian Ehrlicher]

@AndrzejB said in How to use Qt plugins?:

How use plugins? For example in my ImageViewer, is possible dynamic register ?

No need to register something - the plugin just has to be where the Qt version you're using for your program is looking for plugins

How register in system , for GwenView? only in KDE?

See above

What about versions Qt main program and version Qt used to create plugins ? May be different?

The plugin should have compiled with the same Qt version. Plugins compiled with an older version should work too when the main Qt version matches.

[AndrzejB]

I read plugins:

QDir pluginsDir(QApplication::applicationDirPath());
    pluginsDir.cd("plugins");
    foreach (QString filename, pluginsDir.entryList(QDir::Files))
    {
        qDebug() << "Trying to load plugin: " << filename;
        QPluginLoader pl(pluginsDir.absoluteFilePath(filename));
        QObject *plugin = pl.instance();
        if (plugin)
        {
            qDebug() << "Plugin loaded";
        }
        else
        {
            qDebug() << "Failed to load plugin, error: " << pl.errorString();
        }
    }

next I read mime, but not bpg in my list

    QStringList mimeTypeFilters;
    const QByteArrayList supportedMimeTypes = acceptMode == QFileDialog::AcceptOpen
        ? QImageReader::supportedMimeTypes() : QImageWriter::supportedMimeTypes();
    for (const QByteArray &mimeTypeName : supportedMimeTypes) {
        //const char* s = QString(mimeTypeName).toStdString().c_str();
        mimeTypeFilters.append(mimeTypeName);
    }
    mimeTypeFilters.sort();
    dialog.setMimeTypeFilters(mimeTypeFilters);
    dialog.selectMimeTypeFilter("image/bpg");

Plugin has json:

{
    "Keys" : [ "bpg" ],
    "MimeTypes" : ["image/bpg",]
}

[SGaist]

Hi,

The image format plugins should be in a folder named imageformats.

See this Qt Quarterly article.

[AndrzejB]

Now, is Qt5 error in

Q_EXPORT_STATIC_PLUGIN(ArgbPlugin)
Q_EXPORT_PLUGIN2(argb, ArgbPlugin)

Now I found solution:
https://stackoverflow.com/questions/22394477/how-to-create-plugins-qt-5-2-0

Where must be folder imageformats? What is QT_INSTALL_PLUGINS ?
How call install, how migrate from .pro to cmake?
Solved where folder:
https://www.qtcentre.org/threads/46927-Location-of-imageformats-directory