SearchAndBrowseModel QML Type

The SearchAndBrowseModel is a generic model which can be used to search, browse, filter and sort data. More...

Import Statement: import QtIvi 1.0
Instantiates: QIviSearchAndBrowseModel
Inherits:

AbstractFeatureListModel

Properties

Signals

Methods

Detailed Description

The SearchAndBrowseModel 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 SearchAndBrowseModel only fetches the data it really needs and can it can be configured how this can be done.

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

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.
canGoForwardboolTrue if this item can be used to go one level forward and display the next set of items.

Setting it up

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

    SearchAndBrowseModel {
        serviceObject: 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 SearchAndBrowseModel 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 IVI 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 IVI Query Language Documentation.

Browsing

In addition to filtering and sorting, the SearchAndBrowseModel 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 SearchAndBrowseModel provides the following methods/properties for browsing:

Navigation Types

The SearchAndBrowseModel 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.

StackView {
    id: stack
    initialItem: view

    Component {
        id: view
        ListView {
            model: SearchAndBrowseModel {
                contentType: "artist"
            }
            delegate: MouseArea {
                onClicked: {
                    stack.push({ "item" : view,
                                "properties:" {
                                    "model" : model->goForward(index, SearchAndBrowseModel.OutOfModelNavigation)
                                }});
                }
            }
        }
    }
}

Loading Types

Multiple loading types are supported, as the SearchAndBrowseModel is made to work with asynchrounous 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 also goForward().

Property Documentation

availableContentTypes : list<string>

Holds all the available content types

See also contentType.


canGoBack : bool

Holds whether the goBack() function can be used to return to the previous content.

See Browsing for more information.


capabilities : enumeration

Holds the capabilities of the backend for the current content of the model.

The capabilties controls what the current contentType supports. e.g. filtering or sorting. It can be a combination of the following values:

ConstantDescription
NoExtrasThe backend does only support the minimum feature set and is stateful.
SupportsFilteringThe backend supports filtering of the content. QIviSearchAndBrowseModelInterface::availableContentTypes() and QIviSearchAndBrowseModelInterface::supportedIdentifiers() will be used as input for the Qt IVI Query Language.
SupportsSortingThe backend supports sorting of the content. QIviSearchAndBrowseModelInterface::availableContentTypes() and QIviSearchAndBrowseModelInterface::supportedIdentifiers() 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.
SupportsGetSizeThe backend can return the final number of items for a specific request. This makes it possible to support the QIviSearchAndBrowseModel::DataChanged loading type.
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.

See also QIviSearchAndBrowseModelInterface::registerContentType and QIviSearchAndBrowseModelInterface::registerContentType.


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.


contentType : string

Holds the current type of content displayed in this model.

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

See also SearchAndBrowseModel::availableContentTypes.


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.


query : string

Holds the current query used for filtering and sorting the current content of the model.

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

See Qt IVI Query Language for more information.

See also FilteringAndSorting.


Signal Documentation

fetchMoreThresholdReached()

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


Method Documentation

bool canGoForward(i)

Returns true when the item at index i can be used to show the next set of elements.

See also Browsing for more information.


object get(i)

Returns the item at index i.


void goBack()

Goes one level back in the navigation history.

See also Browsing for more information.


SearchAndBrowseModel goForward(i, navigationType)

Uses the item at index i and shows the next set of items.

navigationType can be one of the following values:

ConstantDescription
InModelNavigationThe new content will be loaded into this model and the existing model data will be reset
OutOfModelNavigationA new model will be returned which loads the new content. The model data of this model will not be changed and can still be used.

Note: Whether the OutOfModelNavigation navigation type is supported is decided by the backend.

See also Browsing for more information.


indexOf(SearchAndBrowseModelItem item, object functor)

Determines the index of item in this model and calls the functor once the result is ready. The result is passed as the first argument to the functor and is -1 if the item is not part of the list.

model.indexOf(item, function (index) {
    console.log("The index of item is: ", index)
})

insert(int index, SearchAndBrowseModelItem item)

Insert the item at the position index.

If the backend doesn't accept the provided item, this operation will end in a no op.


move(int cur_index, int new_index)

Moves the item at position cur_index to the new position new_index.


remove(int index)

Removes the item at position index.


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