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

Synopsis¶
Functions¶
def
baseUrl
()def
contextObject
()def
contextProperty
(arg__1)def
engine
()def
isValid
()def
nameForObject
(arg__1)def
parentContext
()def
resolvedUrl
(arg__1)def
setBaseUrl
(arg__1)def
setContextObject
(arg__1)def
setContextProperty
(arg__1, arg__2)def
setContextProperty
(arg__1, arg__2)
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
PySide6.QtQml.
QQmlContext
(parent[, objParent=None])¶ PySide6.QtQml.QQmlContext(parent[, objParent=None])
- Parameters
objParent –
PySide6.QtCore.QObject
parent –
PySide6.QtQml.QQmlContext
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
.
-
PySide6.QtQml.QQmlContext.
baseUrl
()¶ - Return type
Returns the base url of the component, or the containing component if none is set.
See also
-
PySide6.QtQml.QQmlContext.
contextObject
()¶ - Return type
Return the context object, or 0 if there is no context object.
See also
-
PySide6.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 .
See also
-
PySide6.QtQml.QQmlContext.
engine
()¶ - Return type
Return the context’s QQmlEngine
, or 0 if the context has no QQmlEngine
or the QQmlEngine
was destroyed.
-
PySide6.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.
-
PySide6.QtQml.QQmlContext.
nameForObject
(arg__1)¶ - Parameters
arg__1 –
PySide6.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.
-
PySide6.QtQml.QQmlContext.
parentContext
()¶ - Return type
Return the context’s parent QQmlContext
, or 0 if this context has no parent or if the parent has been destroyed.
-
PySide6.QtQml.QQmlContext.
resolvedUrl
(arg__1)¶ - Parameters
arg__1 –
PySide6.QtCore.QUrl
- Return type
Resolves the URL src
relative to the URL of the containing component.
See also
-
PySide6.QtQml.QQmlContext.
setBaseUrl
(arg__1)¶ - Parameters
arg__1 –
PySide6.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.
See also
-
PySide6.QtQml.QQmlContext.
setContextObject
(arg__1)¶ - Parameters
arg__1 –
PySide6.QtCore.QObject
Set the context object
.
See also
-
PySide6.QtQml.QQmlContext.
setContextProperty
(arg__1, arg__2)¶ - Parameters
arg__1 – str
arg__2 –
PySide6.QtCore.QObject
-
PySide6.QtQml.QQmlContext.
setContextProperty
(arg__1, arg__2) - Parameters
arg__1 – str
arg__2 – object
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