QIviPagingModel Class
The QIviPagingModel is a generic model to load its data using the "Paging" aproach. More...
| Header: | #include <QIviPagingModel> |
| qmake: | QT += ivicore |
| Instantiated By: | PagingModel |
| Inherits: | QIviAbstractFeatureListModel |
| Inherited By: |
Public Types
| enum | LoadingType { FetchMore, DataChanged } |
| enum | Roles { NameRole, TypeRole, ItemRole } |
Properties
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Public Functions
| QIviPagingModel(QObject *parent = nullptr) | |
| T | at(int i) const |
| QtIviCoreModule::ModelCapabilities | capabilities() const |
| int | chunkSize() const |
| int | fetchMoreThreshold() const |
| QVariant | get(int i) const |
| QIviPagingModel::LoadingType | loadingType() const |
| void | reload() |
| void | setChunkSize(int chunkSize) |
| void | setFetchMoreThreshold(int fetchMoreThreshold) |
| void | setLoadingType(QIviPagingModel::LoadingType loadingType) |
Reimplemented Public Functions
| virtual bool | canFetchMore(const QModelIndex &parent) const override |
| virtual QVariant | data(const QModelIndex &index, int role) const override |
| virtual void | fetchMore(const QModelIndex &parent) override |
| virtual QHash<int, QByteArray> | roleNames() const override |
| virtual int | rowCount(const QModelIndex &parent = QModelIndex()) const override |
Signals
| void | capabilitiesChanged(QtIviCoreModule::ModelCapabilities capabilities) |
| void | chunkSizeChanged(int chunkSize) |
| void | countChanged() |
| void | fetchMoreThresholdChanged(int fetchMoreThreshold) |
| void | fetchMoreThresholdReached() const |
| void | loadingTypeChanged(QIviPagingModel::LoadingType loadingType) |
Reimplemented Protected Functions
| virtual void | clearServiceObject() override |
| virtual void | connectToServiceObject(QIviServiceObject *serviceObject) override |
| virtual void | disconnectFromServiceObject(QIviServiceObject *serviceObject) override |
Detailed Description
The QIviPagingModel should be used directly or as a base class whenever a lot of data needs to be presented in a ListView.
The model only fetches the data it really needs and can it can be configured how this can be done using the loadingType property.
The backend filling the model with data needs to implement the QIviPagingModelInterface class.
Setting it up
The QIviPagingModel is using QtIviCore's Dynamic Backend System and is derived from QIviAbstractFeatureListModel. Other than most "QtIvi Feature classes", the QIviPagingModel 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:
QIviMediaPlayer *player = new QIviMediaPlayer(); player->startAutoDiscovery(); QIviPagingModel *model = new QIviPagingModel(); model->setServiceObject(player->serviceObject());
Loading Types
Multiple loading types are supported, as the QIviPagingModel is made to work with asynchronous requests to fetch its data. The FetchMore loading type is the default and is using the canFetchMore()/fetchMore() functions of QAbstractItemModel to fetch new data once the view hits the end of the currently available data. As fetching can take some time, there is the fetchMoreThreshold property which controls how much in advance a new fetch should be started.
The other loading type is DataChanged. In contrast to FetchMore, the complete model is pre-populated with empty rows and the actual data for a specific row is fetched the first time the data() function is called. Once the data is available, the dataChanged() signal will be triggered for this row and the view will start to render the new data.
Please see the documentation of LoadingType for more details on how the modes work and when they are suitable to use.
See the Models section for more information about all models in QtIvi.
Member Type Documentation
enum QIviPagingModel::LoadingType
| Constant | Value | Description |
|---|---|---|
QIviPagingModel::FetchMore | 0 | This is the default and can be used if you don't know the final size of the list (e.g. a infinite list). The list will detect that it is near the end (fetchMoreThreshold) and then fetch the next chunk of data using canFetchMore and fetchMore. The drawback of this method is that you can't display a dynamic scroll-bar indicator which is resized depending on the content of the list, because the final size of the data is not known. The other problem could be fast scrolling, as the data might not arrive in-time and scrolling stops. This can be tweaked by the fetchMoreThreshold property. |
QIviPagingModel::DataChanged | 1 | For this loading type you need to know how many items are in the list, as dummy items are created and the user can already start scrolling even though the data is not yet ready to be displayed. Similar to FetchMore, the data is also loaded in chunks. You can safely use a scroll indicator here. The delegate needs to support this approach, as it doesn't have content when it's first created. |
enum QIviPagingModel::Roles
| Constant | Value | Description |
|---|---|---|
QIviPagingModel::NameRole | Qt::DisplayRole | The name of the item. E.g. The name of a contact in a addressbook, or the artist-name in a list of artists. |
QIviPagingModel::TypeRole | Qt::UserRole | The type of the item. E.g. "artist", "track", "contact". |
QIviPagingModel::ItemRole | Qt::UserRole + 1 | The item itself. This provides access to the properties which are type specific. E.g. the address of a contact. |
Property Documentation
capabilities : const QtIviCoreModule::ModelCapabilities
Holds the capabilities of the backend for the current content of the model.
The capabilities controls what the current contentType supports. e.g. filtering or sorting.
Access functions:
| QtIviCoreModule::ModelCapabilities | capabilities() const |
Notifier signal:
| void | capabilitiesChanged(QtIviCoreModule::ModelCapabilities capabilities) |
chunkSize : int
Holds the number of rows which are requested from the backend interface.
This property can be used to fine tune the loading performance.
Bigger chunks means less calls to the backend and to a potential IPC underneath, but more data to be transferred and probably longer waiting time until the request was finished.
Access functions:
| int | chunkSize() const |
| void | setChunkSize(int chunkSize) |
Notifier signal:
| void | chunkSizeChanged(int chunkSize) |
count : const int
Holds the current number of rows in this model.
Access functions:
| virtual int | rowCount(const QModelIndex &parent = QModelIndex()) const override |
Notifier signal:
| void | countChanged() |
fetchMoreThreshold : int
Holds the row delta to the end before the next chunk is loaded
This property can be used to fine tune the loading performance. When the threshold is reached the next chunk of rows are requested from the backend. How many rows are fetched can be defined by using the chunkSize property.
The threshold defines the number of rows before the cached rows ends.
Note: This property is only used when loadingType is set to FetchMore.
Access functions:
| int | fetchMoreThreshold() const |
| void | setFetchMoreThreshold(int fetchMoreThreshold) |
Notifier signal:
| void | fetchMoreThresholdChanged(int fetchMoreThreshold) |
loadingType : QIviPagingModel::LoadingType
Holds the currently used loading type used for loading the data.
Note: When changing this property the content will be reset.
Access functions:
| QIviPagingModel::LoadingType | loadingType() const |
| void | setLoadingType(QIviPagingModel::LoadingType loadingType) |
Notifier signal:
| void | loadingTypeChanged(QIviPagingModel::LoadingType loadingType) |
Member Function Documentation
QIviPagingModel::QIviPagingModel(QObject *parent = nullptr)
Constructs a QIviPagingModel.
The parent argument is passed on to the QIviAbstractFeatureListModel base class.
[signal] void QIviPagingModel::fetchMoreThresholdReached() const
This signal is emitted whenever the fetchMoreThreshold is reached and new data is requested from the backend.
template <typename T> T QIviPagingModel::at(int i) const
Returns the item at index i converted to the template type T.
[override virtual] bool QIviPagingModel::canFetchMore(const QModelIndex &parent) const
Reimplements: QAbstractItemModel::canFetchMore(const QModelIndex &parent) const.
[override virtual protected] void QIviPagingModel::clearServiceObject()
Reimplements: QIviAbstractFeatureListModel::clearServiceObject().
[override virtual protected] void QIviPagingModel::connectToServiceObject(QIviServiceObject *serviceObject)
Reimplements: QIviAbstractFeatureListModel::connectToServiceObject(QIviServiceObject *serviceObject).
[override virtual] QVariant QIviPagingModel::data(const QModelIndex &index, int role) const
Reimplements: QAbstractItemModel::data(const QModelIndex &index, int role) const.
[override virtual protected] void QIviPagingModel::disconnectFromServiceObject(QIviServiceObject *serviceObject)
Reimplements: QIviAbstractFeatureListModel::disconnectFromServiceObject(QIviServiceObject *serviceObject).
[override virtual] void QIviPagingModel::fetchMore(const QModelIndex &parent)
Reimplements: QAbstractItemModel::fetchMore(const QModelIndex &parent).
QVariant QIviPagingModel::get(int i) const
Returns the item at index i as QVariant.
This function is intended to be used from QML. For C++ please use the at() instead.
Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.
void QIviPagingModel::reload()
Resets the model and starts fetching the content again.
Note: This function can be invoked via the meta-object system and from QML. See Q_INVOKABLE.
[override virtual] QHash<int, QByteArray> QIviPagingModel::roleNames() const
Reimplements: QAbstractItemModel::roleNames() const.
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