/**************************************************************************** ** ** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies). ** Contact: http://www.qt-project.org/ ** ** This file is part of the documentation of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:FDL$ ** GNU Free Documentation License ** Alternatively, this file may be used under the terms of the GNU Free ** Documentation License version 1.3 as published by the Free Software ** Foundation and appearing in the file included in the packaging of ** this file. ** ** Other Usage ** Alternatively, this file may be used in accordance with the terms ** and conditions contained in a signed written agreement between you ** and Nokia. ** ** ** ** ** ** $QT_END_LICENSE$ ** ****************************************************************************/ /*! \page qml-c++models.qdoc \title Exposing C++ Models \brief exposing Qt C++ models to the runtime Models can be defined in C++ and then made available to QML. This is useful for exposing existing C++ data models or otherwise complex datasets to QML. A C++ model class can be defined as a \l QStringList, a \l QList or a \l QAbstractItemModel. The first two are useful for exposing simpler datasets, while QAbstractItemModel provides a more flexible solution for more complex models. \section1 QStringList-based Model A model may be a simple \l QStringList, which provides the contents of the list via the \e modelData role. Here is a ListView with a delegate that references its model item's value using the \c modelData role: \snippet examples/declarative/modelviews/stringlistmodel/view.qml 0 A Qt application can load this QML document and set the value of \c myModel to a QStringList: \snippet examples/declarative/modelviews/stringlistmodel/main.cpp 0 The complete example is available in Qt's \l {declarative/modelviews/stringlistmodel}{examples/declarative/modelviews/stringlistmodel} directory. \b{Note:} There is no way for the view to know that the contents of a QStringList have changed. If the QStringList changes, it will be necessary to reset the model by calling QQmlContext::setContextProperty() again. \section1 QObjectList-based model A list of QObject* values can also be used as a model. A QList provides the properties of the objects in the list as roles. The following application creates a \c DataObject class that with Q_PROPERTY values that will be accessible as named roles when a QList is exposed to QML: \snippet examples/declarative/modelviews/objectlistmodel/dataobject.h 0 \dots 4 \snippet examples/declarative/modelviews/objectlistmodel/dataobject.h 1 \codeline \snippet examples/declarative/modelviews/objectlistmodel/main.cpp 0 \dots The QObject* is available as the \c modelData property. As a convenience, the properties of the object are also made available directly in the delegate's context. Here, \c view.qml references the \c DataModel properties in the ListView delegate: \snippet examples/declarative/modelviews/objectlistmodel/view.qml 0 Note the use of the fully qualified access to the \c color property. The properties of the object are not replicated in the \c model object, since they are easily available via the \c modelData object. The complete example is available in Qt's \l {declarative/modelviews/objectlistmodel}{examples/declarative/modelviews/objectlistmodel} directory. Note: There is no way for the view to know that the contents of a QList have changed. If the QList changes, it will be necessary to reset the model by calling QQmlContext::setContextProperty() again. \section1 QAbstractItemModel A model can be defined by subclassing QAbstractItemModel. This is the best approach if you have a more complex model that cannot be supported by the other approaches. A QAbstractItemModel can also automatically notify a QML view when the model data has changed. The roles of a QAbstractItemModel subclass can be exposed to QML by calling QAbstractItemModel::setRoleNames(). The default role names set by Qt are: \table \header \li Qt Role \li QML Role Name \row \li Qt::DisplayRole \li display \row \li Qt::DecorationRole \li decoration \endtable Here is an application with a QAbstractListModel subclass named \c AnimalModel that has \e type and \e size roles. It calls QAbstractItemModel::setRoleNames() to set the role names for accessing the properties via QML: \snippet examples/declarative/modelviews/abstractitemmodel/model.h 0 \dots \snippet examples/declarative/modelviews/abstractitemmodel/model.h 1 \dots \snippet examples/declarative/modelviews/abstractitemmodel/model.h 2 \codeline \snippet examples/declarative/modelviews/abstractitemmodel/model.cpp 0 \codeline \snippet examples/declarative/modelviews/abstractitemmodel/main.cpp 0 \dots This model is displayed by a ListView delegate that accesses the \e type and \e size roles: \snippet examples/declarative/modelviews/abstractitemmodel/view.qml 0 QML views are automatically updated when the model changes. Remember the model must follow the standard rules for model changes and notify the view when the model has changed by using QAbstractItemModel::dataChanged(), QAbstractItemModel::beginInsertRows(), etc. See the \l {Model subclassing reference} for more information. The complete example is available in Qt's \l {declarative/modelviews/abstractitemmodel}{examples/declarative/modelviews/abstractitemmodel} directory. QAbstractItemModel presents a hierarchy of tables, but the views currently provided by QML can only display list data. In order to display child lists of a hierarchical model the VisualDataModel element provides several properties and functions for use with models of type QAbstractItemModel: \list \li \e hasModelChildren role property to determine whether a node has child nodes. \li \l VisualDataModel::rootIndex allows the root node to be specified \li \l VisualDataModel::modelIndex() returns a QModelIndex which can be assigned to VisualDataModel::rootIndex \li \l VisualDataModel::parentModelIndex() returns a QModelIndex which can be assigned to VisualDataModel::rootIndex \endlist \section1 Exposing C++ Data Models to QML The above examples use QQmlContext::setContextProperty() to set model values directly in QML components. An alternative to this is to register the C++ model class as a QML type from a QML C++ plugin using QQmlExtensionPlugin. This would allow the model classes to be created directly as elements within QML: \table \row \li \code class MyModelPlugin : public QQmlExtensionPlugin { public: void registerTypes(const char *uri) { qmlRegisterType(uri, 1, 0, "MyModel"); } } Q_EXPORT_PLUGIN2(mymodelplugin, MyModelPlugin); \endcode \li \qml MyModel { id: myModel ListElement { someProperty: "some value" } } \endqml \qml ListView { width: 200; height: 250 model: myModel delegate: Text { text: someProperty } } \endqml \endtable See \l {Tutorial: Writing QML extensions with C++} for details on writing QML C++ plugins. */