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
importedScript
(name)def
isValid
()def
nameForObject
(arg__1)def
objectForName
(arg__1)def
parentContext
()def
resolvedUrl
(arg__1)def
setBaseUrl
(arg__1)def
setContextObject
(arg__1)def
setContextProperties
(properties)def
setContextProperty
(arg__1, arg__2)def
setContextProperty
(arg__1, arg__2)
Note
This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE
Detailed Description#
Contexts hold the objects identified by id in a QML document. You can use nameForObject()
and objectForName()
to retrieve them.
Note
It is the responsibility of the creator to delete any QQmlContext
it constructs. If a QQmlContext
is no longer needed, it must be destroyed explicitly. The simplest way to ensure this is to give the QQmlContext
a parent.
The Context Hierarchy#
Contexts form a hierarchy. The root of this hierarchy is the QML engine’s root context
. Each QML component creates its own context when instantiated and some QML elements create extra contexts for themselves.
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.
Context Properties#
Contexts also allow data to be exposed to the QML components instantiated by the QML engine. Such data is invisible to any tooling, including the Qt Quick Compiler and to future readers of the QML documents in question. It will only be exposed if the QML component is instantiated in the specific C++ context you are envisioning. In other places, different context data may be exposed instead.
Instead of using the QML context to expose data to your QML components, you should either create additional object properties to hold the data or use singletons
. See Exposing C++ State to QML for a detailed explanation.
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 can be defined and updated by calling setContextProperty()
.
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.
All properties added explicitly by setContextProperty()
take precedence over the context object’s properties.
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.
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 re-evaluate). Thus, if you need to use context properties, you should at least complete the “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 None
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. If you know that the property you’re looking for is a QObject assigned using a QML id in the current context, objectForName()
is more convenient and faster. In contrast to objectForName()
and nameForObject()
, this method does traverse the context hierarchy and searches in parent contexts if the name
is not found in the current one. It also considers any contextObject()
you may have set.
- PySide6.QtQml.QQmlContext.engine()#
- Return type:
Return the context’s QQmlEngine
, or None
if the context has no QQmlEngine
or the QQmlEngine
was destroyed.
- PySide6.QtQml.QQmlContext.importedScript(name)#
- Parameters:
name – str
- Return type:
- 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 as properties of a context object, or by ids in the case of QML created contexts.
If the object has multiple names, the first is returned.
In contrast to contextProperty()
, this method does not traverse the context hierarchy. If the name is not found in the current context, an empty String is returned.
See also
- PySide6.QtQml.QQmlContext.objectForName(arg__1)#
- Parameters:
arg__1 – str
- Return type:
Returns the object for a given name
in this context. Returns nullptr if name
is not available in the context or if the value associated with name
is not a QObject. Objects are named by setContextProperty()
, or as properties of a context object, or by ids in the case of QML created contexts. In contrast to contextProperty()
, this method does not traverse the context hierarchy. If the name is not found in the current context, nullptr is returned.
See also
- PySide6.QtQml.QQmlContext.parentContext()#
- Return type:
Return the context’s parent QQmlContext
, or None
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
.
Note
You should not use context objects to inject values into your QML components. Use singletons or regular object properties instead.
See also
- PySide6.QtQml.QQmlContext.setContextProperties(properties)#
- Parameters:
properties – .list of QQmlContext.PropertyPair
Set a batch of properties
on this context.
Setting all properties in one batch avoids unnecessary refreshing expressions, and is therefore recommended instead of calling setContextProperty()
for each individual property.
Note
You should not use context properties to inject values into your QML components. Use singletons or regular object properties instead.
See also
- PySide6.QtQml.QQmlContext.setContextProperty(arg__1, arg__2)#
- Parameters:
arg__1 – str
arg__2 –
PySide6.QtCore.QObject
Set the value
of the name
property on this context.
QQmlContext
does not take ownership of value
.
Note
You should not use context properties to inject values into your QML components. Use singletons or regular object properties instead.
See also
- PySide6.QtQml.QQmlContext.setContextProperty(arg__1, arg__2)
- Parameters:
arg__1 – str
arg__2 – object
Set a the value
of the name
property on this context.
Note
You should not use context properties to inject values into your QML components. Use singletons or regular object properties instead.