QQmlEngine

The QQmlEngine class provides an environment for instantiating QML components. More

Inheritance diagram of PySide2.QtQml.QQmlEngine

Inherited by: QQmlApplicationEngine

Synopsis

Functions

Slots

Signals

Static functions

Detailed Description

Each QML component is instantiated in a QQmlContext . QQmlContext ‘s are essential for passing data to QML components. In QML, contexts are arranged hierarchically and this hierarchy is managed by the QQmlEngine .

Prior to creating any QML components, an application must have created a QQmlEngine to gain access to a QML context. The following example shows how to create a simple Text item.

QQmlEngine engine;
QQmlComponent component(&engine);
component.setData("import QtQuick 2.0\nText { text: \"Hello world!\" }", QUrl());
QQuickItem *item = qobject_cast<QQuickItem *>(component.create());

//add item to view, etc
...

In this case, the Text item will be created in the engine’s root context .

See also

QQmlComponent QQmlContext QML Global Object

class PySide2.QtQml.QQmlEngine([p=None])

Create a new QQmlEngine with the given parent .

PySide2.QtQml.QQmlEngine.ObjectOwnership

controls whether or not QML automatically destroys the QObject when the corresponding JavaScript object is garbage collected by the engine. The two ownership options are:

Constant

Description

QQmlEngine.CppOwnership

The object is owned by C++ code and QML will never delete it. The JavaScript destroy() method cannot be used on these objects. This option is similar to QScriptEngine::QtOwnership.

QQmlEngine.JavaScriptOwnership

The object is owned by JavaScript. When the object is returned to QML as the return value of a method call, QML will track it and delete it if there are no remaining JavaScript references to it and it has no parent() . An object tracked by one QQmlEngine will be deleted during that QQmlEngine ‘s destructor. Thus, JavaScript references between objects with from two different engines will not be valid if one of these engines is deleted. This option is similar to QScriptEngine::ScriptOwnership.

Generally an application doesn’t need to set an object’s ownership explicitly. QML uses a heuristic to set the default ownership. By default, an object that is created by QML has . The exception to this are the root objects created by calling create() or beginCreate() , which have by default. The ownership of these root-level objects is considered to have been transferred to the C++ caller.

Objects not-created by QML have by default. The exception to this are objects returned from C++ method calls; their ownership will be set to . This applies only to explicit invocations of Q_INVOKABLE methods or slots, but not to property getter invocations.

Calling setObjectOwnership() overrides the default ownership heuristic used by QML.

PySide2.QtQml.QQmlEngine.addImageProvider(id, arg__2)
Parameters

Sets the provider to use for images requested via the image : url scheme, with host providerId . The QQmlEngine takes ownership of provider .

Image providers enable support for pixmap and threaded image requests. See the QQuickImageProvider documentation for details on implementing and using image providers.

All required image providers should be added to the engine before any QML sources files are loaded.

See also

removeImageProvider() QQuickImageProvider QQmlImageProviderBase

PySide2.QtQml.QQmlEngine.addImportPath(dir)
Parameters

dir – str

Adds path as a directory where the engine searches for installed modules in a URL-based directory structure.

The path may be a local filesystem directory, a Qt Resource path (:/imports ), a Qt Resource url (qrc:/imports ) or a URL.

The path will be converted into canonical form before it is added to the import path list.

The newly added path will be first in the importPathList() .

See also

setImportPathList() QML Modules

PySide2.QtQml.QQmlEngine.addNamedBundle(name, fileName)
Parameters
  • name – str

  • fileName – str

Return type

bool

PySide2.QtQml.QQmlEngine.addPluginPath(dir)
Parameters

dir – str

Adds path as a directory where the engine searches for native plugins for imported modules (referenced in the qmldir file).

By default, the list contains only . , i.e. the engine searches in the directory of the qmldir file itself.

The newly added path will be first in the pluginPathList() .

PySide2.QtQml.QQmlEngine.baseUrl()
Return type

PySide2.QtCore.QUrl

Return the base URL for this engine. The base URL is only used to resolve components when a relative URL is passed to the QQmlComponent constructor.

If a base URL has not been explicitly set, this method returns the application’s current working directory.

See also

setBaseUrl()

PySide2.QtQml.QQmlEngine.clearComponentCache()

Clears the engine’s internal component cache.

This function causes the property metadata of all components previously loaded by the engine to be destroyed. All previously loaded components and the property bindings for all extant objects created from those components will cease to function.

This function returns the engine to a state where it does not contain any loaded component data. This may be useful in order to reload a smaller subset of the previous component set, or to load a new version of a previously loaded component.

Once the component cache has been cleared, components must be loaded before any new objects can be created.

static PySide2.QtQml.QQmlEngine.contextForObject(arg__1)
Parameters

arg__1PySide2.QtCore.QObject

Return type

PySide2.QtQml.QQmlContext

Returns the QQmlContext for the object , or 0 if no context has been set.

When the QQmlEngine instantiates a QObject , the context is set automatically.

See also

setContextForObject() qmlContext() qmlEngine()

PySide2.QtQml.QQmlEngine.exit(retCode)
Parameters

retCode – int

PySide2.QtQml.QQmlEngine.imageProvider(id)
Parameters

id – str

Return type

PySide2.QtQml.QQmlImageProviderBase

Returns the image provider set for providerId if found; otherwise returns None .

See also

QQuickImageProvider

PySide2.QtQml.QQmlEngine.importPathList()
Return type

list of strings

Returns the list of directories where the engine searches for installed modules in a URL-based directory structure.

For example, if /opt/MyApp/lib/imports is in the path, then QML that imports com.mycompany.Feature will cause the QQmlEngine to look in /opt/MyApp/lib/imports/com/mycompany/Feature/ for the components provided by that module. A qmldir file is required for defining the type version mapping and possibly QML extensions plugins.

By default, the list contains the directory of the application executable, paths specified in the QML2_IMPORT_PATH environment variable, and the builtin Qml2ImportsPath from QLibraryInfo .

PySide2.QtQml.QQmlEngine.importPlugin(filePath, uri, errors)
Parameters
  • filePath – str

  • uri – str

  • errorsQList

Return type

bool

Imports the plugin named filePath with the uri provided. Returns true if the plugin was successfully imported; otherwise returns false.

On failure and if non-null, the errors list will have any errors which occurred prepended to it.

The plugin has to be a Qt plugin which implements the QQmlEngineExtensionPlugin interface.

PySide2.QtQml.QQmlEngine.incubationController()
Return type

PySide2.QtQml.QQmlIncubationController

Returns the currently set incubation controller, or 0 if no controller has been set.

PySide2.QtQml.QQmlEngine.networkAccessManager()
Return type

PySide2.QtNetwork.QNetworkAccessManager

Returns a common QNetworkAccessManager which can be used by any QML type instantiated by this engine.

If a QQmlNetworkAccessManagerFactory has been set and a QNetworkAccessManager has not yet been created, the QQmlNetworkAccessManagerFactory will be used to create the QNetworkAccessManager ; otherwise the returned QNetworkAccessManager will have no proxy or cache set.

PySide2.QtQml.QQmlEngine.networkAccessManagerFactory()
Return type

PySide2.QtQml.QQmlNetworkAccessManagerFactory

Returns the current QQmlNetworkAccessManagerFactory .

static PySide2.QtQml.QQmlEngine.objectOwnership(arg__1)
Parameters

arg__1PySide2.QtCore.QObject

Return type

ObjectOwnership

Returns the ownership of object .

PySide2.QtQml.QQmlEngine.offlineStorageDatabaseFilePath(databaseName)
Parameters

databaseName – str

Return type

str

Returns the file path where a Local Storage database with the identifier databaseName is (or would be) located.

See also

LocalStorage.openDatabaseSync()

PySide2.QtQml.QQmlEngine.offlineStoragePath()
Return type

str

This property holds the directory for storing offline user data.

Returns the directory where SQL and other offline storage is placed.

The SQL databases created with openDatabase() are stored here.

The default is QML/OfflineStorage in the platform-standard user application data directory.

Note that the path may not currently exist on the filesystem, so callers wanting to create new files at this location should create it first - see mkpath() .

PySide2.QtQml.QQmlEngine.outputWarningsToStandardError()
Return type

bool

Returns true if warning messages will be output to stderr in addition to being emitted by the warnings() signal, otherwise false.

The default value is true.

PySide2.QtQml.QQmlEngine.pluginPathList()
Return type

list of strings

Returns the list of directories where the engine searches for native plugins for imported modules (referenced in the qmldir file).

By default, the list contains only . , i.e. the engine searches in the directory of the qmldir file itself.

PySide2.QtQml.QQmlEngine.quit()
PySide2.QtQml.QQmlEngine.removeImageProvider(id)
Parameters

id – str

Removes the image provider for providerId .

See also

addImageProvider() QQuickImageProvider

PySide2.QtQml.QQmlEngine.retranslate()

Refreshes all binding expressions that use strings marked for translation.

Call this function after you have installed a new translator with installTranslator , to ensure that your user-interface shows up-to-date translations.

Note

Due to a limitation in the implementation, this function refreshes all the engine’s bindings, not only those that use strings marked for translation. This may be optimized in a future release.

PySide2.QtQml.QQmlEngine.rootContext()
Return type

PySide2.QtQml.QQmlContext

Returns the engine’s root context.

The root context is automatically created by the QQmlEngine . Data that should be available to all QML component instances instantiated by the engine should be put in the root context.

Additional data that should only be available to a subset of component instances should be added to sub-contexts parented to the root context.

PySide2.QtQml.QQmlEngine.setBaseUrl(arg__1)
Parameters

arg__1PySide2.QtCore.QUrl

Set the base URL for this engine to url .

See also

baseUrl()

static PySide2.QtQml.QQmlEngine.setContextForObject(arg__1, arg__2)
Parameters

Sets the QQmlContext for the object to context . If the object already has a context, a warning is output, but the context is not changed.

When the QQmlEngine instantiates a QObject , the context is set automatically.

PySide2.QtQml.QQmlEngine.setImportPathList(paths)
Parameters

paths – list of strings

Sets paths as the list of directories where the engine searches for installed modules in a URL-based directory structure.

By default, the list contains the directory of the application executable, paths specified in the QML2_IMPORT_PATH environment variable, and the builtin Qml2ImportsPath from QLibraryInfo .

PySide2.QtQml.QQmlEngine.setIncubationController(arg__1)
Parameters

arg__1PySide2.QtQml.QQmlIncubationController

Sets the engine’s incubation controller . The engine can only have one active controller and it does not take ownership of it.

PySide2.QtQml.QQmlEngine.setNetworkAccessManagerFactory(arg__1)
Parameters

arg__1PySide2.QtQml.QQmlNetworkAccessManagerFactory

Sets the factory to use for creating QNetworkAccessManager (s).

QNetworkAccessManager is used for all network access by QML. By implementing a factory it is possible to create custom QNetworkAccessManager with specialized caching, proxy and cookie support.

The factory must be set before executing the engine.

Note

QQmlEngine does not take ownership of the factory.

static PySide2.QtQml.QQmlEngine.setObjectOwnership(arg__1, arg__2)
Parameters

Sets the ownership of object .

PySide2.QtQml.QQmlEngine.setOfflineStoragePath(dir)
Parameters

dir – str

This property holds the directory for storing offline user data.

Returns the directory where SQL and other offline storage is placed.

The SQL databases created with openDatabase() are stored here.

The default is QML/OfflineStorage in the platform-standard user application data directory.

Note that the path may not currently exist on the filesystem, so callers wanting to create new files at this location should create it first - see mkpath() .

PySide2.QtQml.QQmlEngine.setOutputWarningsToStandardError(arg__1)
Parameters

arg__1 – bool

Set whether warning messages will be output to stderr to enabled .

If enabled is true, any warning messages generated by QML will be output to stderr and emitted by the warnings() signal. If enabled is false, only the warnings() signal will be emitted. This allows applications to handle warning output themselves.

The default value is true.

PySide2.QtQml.QQmlEngine.setPluginPathList(paths)
Parameters

paths – list of strings

Sets the list of directories where the engine searches for native plugins for imported modules (referenced in the qmldir file) to paths .

By default, the list contains only . , i.e. the engine searches in the directory of the qmldir file itself.

PySide2.QtQml.QQmlEngine.setUrlInterceptor(urlInterceptor)
Parameters

urlInterceptorPySide2.QtQml.QQmlAbstractUrlInterceptor

This API is private for 5.1

Sets the urlInterceptor to be used when resolving URLs in QML. This also applies to URLs used for loading script files and QML types. This should not be modifed while the engine is loading files, or URL selection may be inconsistent.

PySide2.QtQml.QQmlEngine.trimComponentCache()

Trims the engine’s internal component cache.

This function causes the property metadata of any loaded components which are not currently in use to be destroyed.

A component is considered to be in use if there are any extant instances of the component itself, any instances of other components that use the component, or any objects instantiated by any of those components.

PySide2.QtQml.QQmlEngine.urlInterceptor()
Return type

PySide2.QtQml.QQmlAbstractUrlInterceptor

This API is private for 5.1

Returns the current QQmlAbstractUrlInterceptor . It must not be modified outside the GUI thread.

PySide2.QtQml.QQmlEngine.warnings(warnings)
Parameters

warnings