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Diffstat (limited to 'src/declarative/qml/qdeclarativecontext.cpp')
| -rw-r--r-- | src/declarative/qml/qdeclarativecontext.cpp | 85 |
1 files changed, 40 insertions, 45 deletions
diff --git a/src/declarative/qml/qdeclarativecontext.cpp b/src/declarative/qml/qdeclarativecontext.cpp index 2b8cf70..a9224ad 100644 --- a/src/declarative/qml/qdeclarativecontext.cpp +++ b/src/declarative/qml/qdeclarativecontext.cpp @@ -71,31 +71,30 @@ QDeclarativeContextPrivate::QDeclarativeContextPrivate() Contexts allow data to be exposed to the QML components instantiated by the QML engine. - Each QDeclarativeContext contains a set of properties, distinct from - its QObject properties, that allow data to be - explicitly bound to a context by name. The context properties are defined or - updated by calling QDeclarativeContext::setContextProperty(). The following example shows - a Qt model being bound to a context and then accessed from a QML file. + Each QDeclarativeContext contains a set of properties, distinct from its QObject + properties, that allow data to be explicitly bound to a context by name. The + context properties are defined and updated by calling + QDeclarativeContext::setContextProperty(). The following example shows a Qt model + being bound to a context and then accessed from a QML file. \code QDeclarativeEngine engine; - QDeclarativeContext context(engine.rootContext()); - context.setContextProperty("myModel", modelData); + QDeclarativeContext *context = new QDeclarativeContext(engine.rootContext()); + context->setContextProperty("myModel", modelData); QDeclarativeComponent component(&engine, "ListView { model=myModel }"); - component.create(&context); + component.create(context); \endcode - To simplify binding and maintaining larger data sets, QObject's can be - added to a QDeclarativeContext. These objects are known as the context's default - objects. In this case all the properties of the QObject are - made available by name in the context, as though they were all individually - added by calling QDeclarativeContext::setContextProperty(). Changes to the property's - values are detected through the property's notify signal. This method is - also slightly more faster than manually adding property values. + To simplify binding and maintaining larger data sets, a context object can be set + on a QDeclarativeContext. All the properties of the context object are available + by name in the context, as though they were all individually added through calls + to QDeclarativeContext::setContextProperty(). Changes to the property's values are + detected through the property's notify signal. Setting a context object is both + faster and easier than manually adding and maintaing context property values. - The following example has the same effect as the one above, but it is - achieved using a default object. + The following example has the same effect as the previous one, but it uses a context + object. \code class MyDataSet : ... { @@ -104,46 +103,42 @@ QDeclarativeContextPrivate::QDeclarativeContextPrivate() ... }; - MyDataSet myDataSet; + MyDataSet *myDataSet = new MyDataSet; QDeclarativeEngine engine; - QDeclarativeContext context(engine.rootContext()); - context.setContextObject(&myDataSet); + QDeclarativeContext *context = new QDeclarativeContext(engine.rootContext()); + context->setContextObject(myDataSet); QDeclarativeComponent component(&engine, "ListView { model=myModel }"); - component.create(&context); + component.create(context); \endcode - Default objects added first take precedence over those added later. All properties - added explicitly by QDeclarativeContext::setContextProperty() take precedence over default - object properties. + All properties added explicitly by QDeclarativeContext::setContextProperty() take + precedence over context object's properties. - Contexts are hierarchal, with the \l {QDeclarativeEngine::rootContext()}{root context} - being created by the QDeclarativeEngine. A component instantiated in a given context - has access to that context's data, as well as the data defined by its - ancestor contexts. Data values (including those added implicitly by the - default objects) in a context override those in ancestor contexts. Data - that should be available to all components instantiated by the QDeclarativeEngine - should be added to the \l {QDeclarativeEngine::rootContext()}{root context}. + Contexts form a hierarchy. The root of this heirarchy is the QDeclarativeEngine's + \l {QDeclarativeEngine::rootContext()}{root context}. A component instance can + access the data in its own context, as well as all its ancestor contexts. Data + can be made available to all instances by modifying the + \l {QDeclarativeEngine::rootContext()}{root context}. - In the following example, + The following example defines two contexts - \c context1 and \c context2. The + second context overrides the "b" context property inherited from the first with a + new value. \code QDeclarativeEngine engine; - QDeclarativeContext context1(engine.rootContext()); - QDeclarativeContext context2(&context1); - QDeclarativeContext context3(&context2); - - context1.setContextProperty("a", 12); - context2.setContextProperty("b", 13); - context3.setContextProperty("a", 14); - context3.setContextProperty("c", 14); + QDeclarativeContext *context1 = new QDeclarativeContext(engine.rootContext()); + QDeclarativeContext *context2 = new QDeclarativeContext(context1); + + context1->setContextProperty("a", 12); + context1->setContextProperty("b", 12); + + context2->setContextProperty("b", 15); \endcode - a QML component instantiated in context1 would have access to the "a" data, - a QML component instantiated in context2 would have access to the "a" and - "b" data, and a QML component instantiated in context3 would have access to - the "a", "b" and "c" data - although its "a" data would return 14, unlike - that in context1 or context2. + While QML objects instantiated in a context are not strictly owned by that + context, their bindings are. If a context is destroyed, the property bindings of + outstanding QML objects will stop evaluating. */ /*! \internal */ |