class QQmlContext#

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

Synopsis#

Methods#

def __init__()
def baseUrl()
def contextObject()
def contextProperty()
def engine()
def importedScript()
def isValid()
def nameForObject()
def objectForName()
def parentContext()
def resolvedUrl()
def setBaseUrl()
def setContextObject()
def setContextProperties()
def setContextProperty()

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

__init__(parent[, objParent=None])#

Parameters:

parent – QQmlEngine
objParent – QObject

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

__init__(parent[, objParent=None])

Parameters:

parent – QQmlContext
objParent – QObject

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

baseUrl()#

Return type:: QUrl

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

See also

setBaseUrl()

contextObject()#

Return type:: QObject

Return the context object, or None if there is no context object.

See also

setContextObject()

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.

See also

setContextProperty() objectForName() nameForObject() contextObject()

engine()#

Return type:: QQmlEngine

Return the context’s QQmlEngine , or None if the context has no QQmlEngine or the QQmlEngine was destroyed.

importedScript(name)#

Parameters:: name – str
Return type:: QJSValue

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.

nameForObject(arg__1)#

Parameters:: arg__1 – 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

contextProperty() objectForName()

objectForName(arg__1)#

Parameters:: arg__1 – str
Return type:: QObject

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

contextProperty() nameForObject()

parentContext()#

Return type:: QQmlContext

Return the context’s parent QQmlContext , or None if this context has no parent or if the parent has been destroyed.

resolvedUrl(arg__1)#

Parameters:: arg__1 – QUrl
Return type:: QUrl

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

See also

baseUrl() setBaseUrl()

setBaseUrl(arg__1)#

Parameters:: arg__1 – 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

baseUrl() resolvedUrl()

setContextObject(arg__1)#

Parameters:: arg__1 – 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

contextObject()

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

setContextProperty()

setContextProperty(arg__1, arg__2)#

Parameters:

arg__1 – str
arg__2 – 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

contextProperty()

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.