FolderListModel - a C++ model plugin

Defining the Model

We are subclassing QAbstractListModel which will allow us to give data to QML and send notifications when the data changes:

As you see, we also inherit the QDeclarativeParserStatus interface, so that we can delay initial processing until we have all properties set (via componentComplete() below).

The first thing to do when devising a new type for QML is to define the properties you want the type to have:

The purposes of each of these should be pretty obvious - in QML we will set the folder to display (a file: URL), and the kinds of files we want to show in the view of the model.

Next are the constructor, destructor, and standard QAbstractListModel subclassing requirements:

The data() function is where we provide model values. The rowCount() function is also a standard part of the QAbstractListModel interface, but we also want to provide a simpler count property:

Then we have the functions for the remaining properties which we defined above:

Imperative actions upon the model are made available to QML via a Q_INVOKABLE tag on a normal member function. The isFolder(index) function says whether the value at index is a folder:

Then we have the QDeclarativeParserStatus interface:

Then the NOTIFY function for the folders property. The implementation will emit this when the folder property is changed.

The class ends with some implementation details:

Lastly, the boilerplare to declare the type for QML use:

 class QmlFolderListModelPlugin : public QQmlExtensionPlugin
 {
     Q_OBJECT
     Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QQmlExtensionInterface" FILE "folderlistmodel.json")

 public:
     virtual void registerTypes(const char *uri)
     {
         Q_ASSERT(QLatin1String(uri) == QLatin1String("Qt.labs.folderlistmodel"));
 #ifndef QT_NO_DIRMODEL
         qmlRegisterType<QQuickFolderListModel>(uri,1,0,"FolderListModel");
 #endif
     }
 };