QQmlContext

The QQmlContext class defines a context within a QML engine. More

Inheritance diagram of PySide2.QtQml.QQmlContext

Synopsis

Functions

Detailed Description

Contexts allow data to be exposed to the QML components instantiated by the QML engine.

Each QQmlContext 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 setContextProperty() . The following example shows a Qt model being bound to a context and then accessed from a QML file.

QQmlEngine engine;
QStringListModel modelData;
QQmlContext *context = new QQmlContext(engine.rootContext());
context->setContextProperty("myModel", &modelData);

QQmlComponent component(&engine);
component.setData("import QtQuick 2.0\nListView { model: myModel }", QUrl());
QObject *window = component.create(context);

Note it is the responsibility of the creator to delete any QQmlContext it constructs. If the context object in the example is no longer needed when the window component instance is destroyed, the context must be destroyed explicitly. The simplest way to ensure this is to set window as the parent of context .

To simplify binding and maintaining larger data sets, a context object can be set on a QQmlContext . All the properties of the context object are available by name in the context, as though they were all individually added through calls to 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 maintaining context property values.

The following example has the same effect as the previous one, but it uses a context object.

class MyDataSet : ... {
    ...
    Q_PROPERTY(QAbstractItemModel *myModel READ model NOTIFY modelChanged)
    ...
};

MyDataSet myDataSet;
QQmlEngine engine;
QQmlContext *context = new QQmlContext(engine.rootContext());
context->setContextObject(&myDataSet);

QQmlComponent component(&engine);
component.setData("import QtQuick 2.0\nListView { model: myModel }", QUrl());
component.create(context);

All properties added explicitly by setContextProperty() take precedence over the context object’s properties.

The Context Hierarchy

Contexts form a hierarchy. The root of this hierarchy is the QML engine’s root context . Child contexts inherit the context properties of their parents; if a child context sets a context property that already exists in its parent, the new context property overrides that of the parent.

The following example defines two contexts - context1 and context2 . The second context overrides the “b” context property inherited from the first with a new value.

QQmlEngine engine;
QQmlContext *context1 = new QQmlContext(engine.rootContext());
QQmlContext *context2 = new QQmlContext(context1);

context1->setContextProperty("a", 12);
context1->setContextProperty("b", 12);

context2->setContextProperty("b", 15);

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.

Warning

Setting the context object or adding new context properties after an object has been created in that context is an expensive operation (essentially forcing all bindings to reevaluate). Thus whenever possible you should complete “setup” of the context before using it to create any objects.

See also

Exposing Attributes of C++ Types to QML

class PySide2.QtQml.QQmlContext(parent[, objParent=None])

PySide2.QtQml.QQmlContext(parent[, objParent=None])

param parent

PySide2.QtQml.QQmlContext

param objParent

PySide2.QtCore.QObject

Create a new QQmlContext with the given parentContext , and the QObject parent .

Create a new QQmlContext as a child of engine ‘s root context, and the QObject parent .

PySide2.QtQml.QQmlContext.baseUrl()
Return type

PySide2.QtCore.QUrl

Returns the base url of the component, or the containing component if none is set.

See also

setBaseUrl()

PySide2.QtQml.QQmlContext.contextObject()
Return type

PySide2.QtCore.QObject

Return the context object, or 0 if there is no context object.

PySide2.QtQml.QQmlContext.contextProperty(arg__1)
Parameters

arg__1 – str

Return type

object

Returns the value of the name property for this context as a QVariant .

PySide2.QtQml.QQmlContext.engine()
Return type

PySide2.QtQml.QQmlEngine

Return the context’s QQmlEngine , or 0 if the context has no QQmlEngine or the QQmlEngine was destroyed.

PySide2.QtQml.QQmlContext.isValid()
Return type

bool

Returns whether the context is valid.

To be valid, a context must have a engine, and it’s contextObject() , if any, must not have been deleted.

PySide2.QtQml.QQmlContext.nameForObject(arg__1)
Parameters

arg__1PySide2.QtCore.QObject

Return type

str

Returns the name of object in this context, or an empty string if object is not named in the context. Objects are named by setContextProperty() , or by ids in the case of QML created contexts.

If the object has multiple names, the first is returned.

PySide2.QtQml.QQmlContext.parentContext()
Return type

PySide2.QtQml.QQmlContext

Return the context’s parent QQmlContext , or 0 if this context has no parent or if the parent has been destroyed.

PySide2.QtQml.QQmlContext.resolvedUrl(arg__1)
Parameters

arg__1PySide2.QtCore.QUrl

Return type

PySide2.QtCore.QUrl

Resolves the URL src relative to the URL of the containing component.

PySide2.QtQml.QQmlContext.setBaseUrl(arg__1)
Parameters

arg__1PySide2.QtCore.QUrl

Explicitly sets the url resolvedUrl() will use for relative references to baseUrl .

Calling this function will override the url of the containing component used by default.

PySide2.QtQml.QQmlContext.setContextObject(arg__1)
Parameters

arg__1PySide2.QtCore.QObject

Set the context object .

See also

contextObject()

PySide2.QtQml.QQmlContext.setContextProperty(arg__1, arg__2)
Parameters
PySide2.QtQml.QQmlContext.setContextProperty(arg__1, arg__2)
Parameters
  • arg__1 – str

  • arg__2 – object