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/****************************************************************************
**
** 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<QObject*> 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<QObject*> 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<DataObject*> 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<MyModel>(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.
*/
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