QIfFilterAndBrowseModel Class

Detailed Description

The QIfFilterAndBrowseModel should be used directly or as a base class whenever a lot of data needs to be presented in a ListView.

The model is built upon the basic principle of filtering and sorting the data already where they are created instead of retrieving everything and sort or filter it locally. In addition the QIfFilterAndBrowseModel only fetches the data it really needs and can it can be configured how this can be done.

The backend filling the model with data needs to implement the QIfFilterAndBrowseModelInterface class.

Setting it up

The QIfFilterAndBrowseModel is using QtInterfaceFramework's Dynamic Backend System and is derived from QIfAbstractFeatureListModel. Other than most "QtInterfaceFramework Feature classes", the QIfFilterAndBrowseModel doesn't automatically connect to available backends.

The easiest approach to set it up, is to connect to the same backend used by another feature. E.g. for connecting to the media backend, use the instance from the mediaplayer feature:

QIfMediaPlayer *player = new QIfMediaPlayer();
player->startAutoDiscovery();
QIfFilterAndBrowseModel *model = new QIfFilterAndBrowseModel();
model->setServiceObject(player->serviceObject());

Content Types

Once the model is connected to a backend, the contentType needs to be selected. All possible content types can be queried from the availableContentTypes property. As the name already suggests, this property selects what type of content should be shown in the model. For the mediaplayer example, the available content types could be "track", "album" and "artist".

Filtering and Sorting

One of the main use case of the QIfFilterAndBrowseModel is to provide a powerful way of filtering and sorting the content of the underlying data model. As explained above, the filtering and sorting is supposed to happen where the data is produced. To make this work across multiple backends the Qt Interface Framework Query Language was invented.

The query property is used to sort the content of the model: e.g. by setting the string "[/name]", the content will be sorted by name in ascending order.

For filtering, the same property is used but without the brackets e.g. "name='Example Item'" for only showing items which have the 'name' property set to 'Example Item'.

Filtering and sorting can also be combined in one string and the filter part can also be more complex. More on that can be found in the detailed Qt Interface Framework Query Language Documentation.

Browsing

In addition to filtering and sorting, the QIfFilterAndBrowseModel also supports browsing through a hierarchy of different content types. The easiest way to explain this is to look at the existing media example.

When implementing a library view of all available media files, you might want to provide a way for the user to browse through the media database and select a song. You might also want to provide several staring points and from there limit the results. E.g.

• Artist -> Album -> Track
• Album -> Track
• Track

This can be achieved by defining a complex filter query which takes the previously selected item into account. That is the most powerful way of doing it, as the developer/designer can define the browsing order and it can easily be changed. The downside of this is that the backend needs to support this way of filtering and sorting as well, which is not always be the case. A good example here is a DLNA backend, where the server already defines a fixed browsing order.

The QIfFilterAndBrowseModel provides the following methods for browsing:

• canGoForward()
• goForward()
• canGoBack()
• goBack()

Navigation Types

The QIfFilterAndBrowseModel supports two navigation types when browsing through the available data: for most use cases the simple InModelNavigation type is sufficient. By using this, the content type of the current model instance changes when navigating and the model is reset to show the new data. The other navigation type is OutOfModelNavigation and leaves the current model instance as it is. Instead the goForward() method returns a new model instance which contains the new data. This is especially useful when several views need to be open at the same time. E.g. when used inside a QML StackView.

QIfFilterAndBrowseModel *artistModel = new QIfFilterAndBrowseModel();
model->setContentType("artist");
//Returns a new instance of QIfFilterAndBrowseModel which contains all albums from the artist at index '0'
QIfFilterAndBrowseModel *albumModel = artistModel->goForward(0, QIfFilterAndBrowseModel::OutOfModelNavigation);