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# QDeclarativeEngine Class Reference
[QtDeclarative module]

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

Inherits QObject.

### Types

- enum ObjectOwnership { CppOwnership, JavaScriptOwnership }

### Methods

- __init__ (self, QObject parent = None)
- addImageProvider (self, QString id, QDeclarativeImageProvider)
- addImportPath (self, QString dir)
- addPluginPath (self, QString dir)
- QUrl baseUrl (self)
- clearComponentCache (self)
- QDeclarativeImageProvider imageProvider (self, QString id)
- QStringList importPathList (self)
- (bool, QString errorString) importPlugin (self, QString filePath, QString uri)
- QNetworkAccessManager networkAccessManager (self)
- QDeclarativeNetworkAccessManagerFactory networkAccessManagerFactory (self)
- QString offlineStoragePath (self)
- bool outputWarningsToStandardError (self)
- QStringList pluginPathList (self)
- removeImageProvider (self, QString id)
- QDeclarativeContext rootContext (self)
- setBaseUrl (self, QUrl)
- setImportPathList (self, QStringList paths)
- setNetworkAccessManagerFactory (self, QDeclarativeNetworkAccessManagerFactory)
- setOfflineStoragePath (self, QString dir)
- setOutputWarningsToStandardError (self, bool)
- setPluginPathList (self, QStringList paths)

### Static Methods

- QDeclarativeContext contextForObject (QObject)
- ObjectOwnership objectOwnership (QObject)
- setContextForObject (QObject, QDeclarativeContext)
- setObjectOwnership (QObject, ObjectOwnership)

### Qt Signals

- void quit ()
- void warnings (const QList<QDeclarativeError>&)

## Detailed Description

The QDeclarativeEngine class provides an environment for instantiating QML components.

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

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

     QDeclarativeEngine engine;
     QDeclarativeComponent component(&engine);
     component.setData("import QtQuick 1.0\nText { text: \"Hello world!\" }", QUrl());
     QDeclarativeItem *item = qobject_cast<QDeclarativeItem *>(component.create());

     //add item to view, etc
     ...

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

## Type Documentation

### QDeclarativeEngine.ObjectOwnership

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

Constant | Value | Description
--- | --- | ---
`QDeclarativeEngine.CppOwnership` | `0` | The object is owned by C++ code, and will never be deleted by QML. The JavaScript destroy() method cannot be used on objects with CppOwnership. This option is similar to QScriptEngine.QtOwnership.
`QDeclarativeEngine.JavaScriptOwnership` | `1` | The object is owned by JavaScript. When the object is returned to QML as the return value of a method call or property access, QML will delete the object if there are no remaining JavaScript references to it and it has no QObject.parent(). 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 object ownership. By default, an object that is created by QML has JavaScriptOwnership. The exception to this are the root objects created by calling QDeclarativeCompnent.create() or QDeclarativeComponent.beginCreate() which have CppOwnership 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 CppOwnership by default. The exception to this is objects returned from a C++ method call. The ownership of these objects is passed to JavaScript.

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

## Method Documentation

### QDeclarativeEngine.__init__ (self, QObject parent = None)

The parent argument, if not None, causes self to be owned by Qt instead of PyQt.

Create a new QDeclarativeEngine with the given parent.

### QDeclarativeEngine.addImageProvider (self, QString id, QDeclarativeImageProvider)

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

Image providers enable support for pixmap and threaded image requests. See the QDeclarativeImageProvider 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.

Note that images loaded from a QDeclarativeImageProvider are cached by QPixmapCache, similar to any image loaded by QML.

See also removeImageProvider().

### QDeclarativeEngine.addImportPath (self, QString dir)

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 or a URL.

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

See also setImportPathList() and QML Modules.

### QDeclarativeEngine.addPluginPath (self, QString dir)

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().

See also setPluginPathList().

### QUrl QDeclarativeEngine.baseUrl (self)

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

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

See also setBaseUrl().

### QDeclarativeEngine.clearComponentCache (self)

Clears the engine's internal component cache.

Normally the QDeclarativeEngine caches components loaded from qml files. This method clears this cache and forces the component to be reloaded.

### QDeclarativeContext QDeclarativeEngine.contextForObject (QObject)

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

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

See also setContextForObject().

### QDeclarativeImageProvider QDeclarativeEngine.imageProvider (self, QString id)

Returns the QDeclarativeImageProvider set for providerId.

### QStringList QDeclarativeEngine.importPathList (self)

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 QDeclarativeEngine 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 declarative extensions plugins.

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

See also addImportPath() and setImportPathList().

### (bool, QString errorString) QDeclarativeEngine.importPlugin (self, QString filePath, QString uri)

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, *errorString will be set to a message describing the failure.

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

### QNetworkAccessManager QDeclarativeEngine.networkAccessManager (self)

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

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

See also setNetworkAccessManagerFactory().

### QDeclarativeNetworkAccessManagerFactory QDeclarativeEngine.networkAccessManagerFactory (self)

Returns the current QDeclarativeNetworkAccessManagerFactory.

See also setNetworkAccessManagerFactory().

### ObjectOwnership QDeclarativeEngine.objectOwnership (QObject)

Returns the ownership of object.

See also setObjectOwnership().

### QString QDeclarativeEngine.offlineStoragePath (self)

### bool QDeclarativeEngine.outputWarningsToStandardError (self)

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.

See also setOutputWarningsToStandardError().

### QStringList QDeclarativeEngine.pluginPathList (self)

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.

See also addPluginPath() and setPluginPathList().

### QDeclarativeEngine.removeImageProvider (self, QString id)

Removes the QDeclarativeImageProvider for providerId.

Returns the provider if it was found; otherwise returns 0.

See also addImageProvider().

### QDeclarativeContext QDeclarativeEngine.rootContext (self)

Returns the engine's root context.

The root context is automatically created by the QDeclarativeEngine. 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.

### QDeclarativeEngine.setBaseUrl (self, QUrl)

Set the base URL for this engine to url.

See also baseUrl().

### QDeclarativeEngine.setContextForObject (QObject, QDeclarativeContext)

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

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

See also contextForObject().

### QDeclarativeEngine.setImportPathList (self, QStringList paths)

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 `QML_IMPORT_PATH` environment variable, and the builtin `ImportsPath` from QLibraryInfo.

See also importPathList() and addImportPath().

### QDeclarativeEngine.setNetworkAccessManagerFactory (self, QDeclarativeNetworkAccessManagerFactory)

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.

See also networkAccessManagerFactory().

### QDeclarativeEngine.setObjectOwnership (QObject, ObjectOwnership)

Sets the ownership of object.

See also objectOwnership().

### QDeclarativeEngine.setOfflineStoragePath (self, QString dir)

### QDeclarativeEngine.setOutputWarningsToStandardError (self, 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, on the warnings() signal will be emitted. This allows applications to handle warning output themselves.

The default value is true.

See also outputWarningsToStandardError().

### QDeclarativeEngine.setPluginPathList (self, QStringList paths)

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.

See also pluginPathList() and addPluginPath().

## Qt Signal Documentation

### void quit ()

This is the default overload of this signal.

This signal is emitted when the QML loaded by the engine would like to quit.

### void warnings (const QList<QDeclarativeError>&)

This is the default overload of this signal.

This signal is emitted when warnings messages are generated by QML.