PagingModel QML Type

The PagingModel is a generic model to load its data using the "Paging" aproach. More...

Import Statement: import QtIvi 1.0
Instantiates: QIviPagingModel
Inherits:

AbstractFeatureListModel

Inherited By:

SearchAndBrowseModel

Properties

Signals

Methods

Detailed Description

The PagingModel 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.

All rows in the model need to be subclassed from StandardItem.

The following roles are available in this model:

Role nameTypeDescription
namestringThe name of the item. E.g. The name of a contact in a addressbook, or the artist-name in a list of artists.
typestringThe type of the item. E.g. "artist", "track", "contact".
itemobjectThe item itself. This provides access to the properties which are type specific. E.g. the address of a contact.

Setting it up

The PagingModel is using QtIviCore's Dynamic Backend System and is derived from QIviAbstractFeatureListModel. Other than most "QtIvi Feature classes", the PagingModel 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:

Item {
    MediaPlayer {
        id: player
    }

    PagingModel {
        serviceObject: player.serviceObject
    }
}

Loading Types

Multiple loading types are supported, as the PagingModel 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.

Property Documentation

capabilities : enumeration

Holds the capabilities of the backend.

The capabilities controls what the backend supports. It can be a combination of the following values:

ConstantDescription
NoExtrasThe backend does only support the minimum feature set and is stateful.
SupportsGetSizeThe backend can return the final number of items for a specific request. This makes it possible to support the QIviPagingModel::DataChanged loading type.
SupportsFilteringThe backend supports filtering of the content. QIviSearchAndBrowseModelInterface::availableContentTypesChanged() and QIviSearchAndBrowseModelInterface::queryIdentifiersChanged() will be used as input for the Qt IVI Query Language.
SupportsSortingThe backend supports sorting of the content. QIviSearchAndBrowseModelInterface::availableContentTypesChanged() and QIviSearchAndBrowseModelInterface::queryIdentifiersChanged() will be used as input for the Qt IVI Query Language.
SupportsAndConjunctionThe backend supports handling multiple filters at the same time and these filters can be combined by using the AND conjunction.
SupportsOrConjunctionThe backend supports handling multiple filters at the same time and these filters can be combined by using the OR conjunction.
SupportsStatelessNavigationThe backend is stateless and supports handling multiple instances of a QIviSearchAndBrowseModel requesting different data at the same time. E.g. One request for artists, sorted by name and another request for tracks. The backend has to consider that both request come from models which are currently visible at the same time.
SupportsInsertThe backend supports inserting new items at a given position.
SupportsMoveThe backend supports moving items within the model.
SupportsRemoveThe backend supports removing items from the model.

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.


count : int

Holds the current number of rows in this model.


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.


loadingType : enumeration

Holds the currently used loading type used for loading the data.

It can be one of the following values:

ConstantDescription
FetchMoreThis 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.
DataChangedFor 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.

Note: When changing this property the content will be reset.


Signal Documentation

fetchMoreThresholdReached()

This signal is emitted whenever the fetchMoreThreshold is reached and new data is requested from the backend.


Method Documentation

object get(i)

Returns the item at index i.


reload()

Resets the model and starts fetching the content again.


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