class QQuickWidget¶

The QQuickWidget class provides a widget for displaying a Qt Quick user interface. More…

Synopsis¶

Properties¶

resizeModeᅟ - Determines whether the view should resize the window contents
sourceᅟ - URL of the source of the QML component
statusᅟ

Methods¶

def __init__()
def engine()
def errors()
def format()
def grabFramebuffer()
def initialSize()
def quickWindow()
def resizeMode()
def rootContext()
def rootObject()
def setClearColor()
def setFormat()
def setResizeMode()
def source()
def status()

Signals¶

def sceneGraphError()
def statusChanged()

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¶

This is a convenience wrapper for QQuickWindow which will automatically load and display a QML scene when given the URL of the main source file. Alternatively, you can instantiate your own objects using QQmlComponent and place them in a manually set up QQuickWidget .

Typical usage:

QQuickWidget *view = new QQuickWidget;
view->setSource(QUrl::fromLocalFile("myqmlfile.qml"));
view->show();

To receive errors related to loading and executing QML with QQuickWidget , you can connect to the statusChanged() signal and monitor for Error . The errors are available via errors() .

QQuickWidget also manages sizing of the view and root object. By default, the resizeMode is SizeViewToRootObject , which will load the component and resize it to the size of the view. Alternatively the resizeMode may be set to SizeRootObjectToView which will resize the view to the size of the root object.

Performance Considerations¶

QQuickWidget is an alternative to using QQuickView and QWidget::createWindowContainer(). The restrictions on stacking order do not apply, making QQuickWidget the more flexible alternative, behaving more like an ordinary widget.

However, the above mentioned advantages come at the expense of performance:

Unlike QQuickWindow and QQuickView , QQuickWidget involves at least one additional render pass targeting an offscreen color buffer, typically a 2D texture, followed by drawing a texture quad. This means increased load especially for the fragment processing of the GPU.

Using QQuickWidget disables the threaded render loop on all platforms. This means that some of the benefits of threaded rendering, for example Animator classes and vsync driven animations, will not be available.

Note

Avoid calling winId() on a QQuickWidget . This function triggers the creation of a native window, resulting in reduced performance and possibly rendering glitches. The entire purpose of QQuickWidget is to render Quick scenes without a separate native window, hence making it a native widget should always be avoided.

Graphics API Support¶

QQuickWidget is functional with all the 3D graphics APIs supported by Qt Quick, as well as the software backend. Other backends, for example OpenVG, are not compatible however and attempting to construct a QQuickWidget will lead to problems.

Overriding the platform’s default graphics API is done the same way as with QQuickWindow and QQuickView : either by calling setGraphicsApi() early on before constructing the first QQuickWidget , or by setting the QSG_RHI_BACKEND environment variable.

Note

One top-level window can only use one single graphics API for rendering. For example, attempting to place a QQuickWidget using Vulkan and a QOpenGLWidget in the widget hierarchy of the same top-level window, problems will occur and one of the widgets will not be rendering as expected.

Scene Graph and Context Persistency¶

QQuickWidget honors isPersistentSceneGraph() , meaning that applications can decide - by calling setPersistentSceneGraph() on the window returned from the quickWindow() function - to let scenegraph nodes and other Qt Quick scene related resources be released whenever the widget becomes hidden. By default persistency is enabled, just like with QQuickWindow .

When running with the OpenGL, QQuickWindow offers the possibility to disable persistent OpenGL contexts as well. This setting is currently ignored by QQuickWidget and the context is always persistent. The OpenGL context is thus not destroyed when hiding the widget. The context is destroyed only when the widget is destroyed or when the widget gets reparented into another top-level widget’s child hierarchy. However, some applications, in particular those that have their own graphics resources due to performing custom OpenGL rendering in the Qt Quick scene, may wish to disable the latter since they may not be prepared to handle the loss of the context when moving a QQuickWidget into another window. Such applications can set the QCoreApplication::AA_ShareOpenGLContexts attribute. For a discussion on the details of resource initialization and cleanup, refer to the QOpenGLWidget documentation.

Note

QQuickWidget offers less fine-grained control over its internal OpenGL context than QOpenGLWidget, and there are subtle differences, most notably that disabling the persistent scene graph will lead to destroying the context on a window change regardless of the presence of QCoreApplication::AA_ShareOpenGLContexts.

Limitations¶

Putting other widgets underneath and making the QQuickWidget transparent will not lead to the expected results: the widgets underneath will not be visible. This is because in practice the QQuickWidget is drawn before all other regular, non-OpenGL widgets, and so see-through types of solutions are not feasible. Other type of layouts, like having widgets on top of the QQuickWidget , will function as expected.

When absolutely necessary, this limitation can be overcome by setting the Qt::WA_AlwaysStackOnTop attribute on the QQuickWidget . Be aware, however that this breaks stacking order. For example it will not be possible to have other widgets on top of the QQuickWidget , so it should only be used in situations where a semi-transparent QQuickWidget with other widgets visible underneath is required.

This limitation only applies when there are other widgets underneath the QQuickWidget inside the same window. Making the window semi-transparent, with other applications and the desktop visible in the background, is done in the traditional way: Set Qt::WA_TranslucentBackground on the top-level window, request an alpha channel, and change the Qt Quick Scenegraph’s clear color to Qt::transparent via setClearColor() .

Tab Key Handling¶

On press of the [TAB] key, the item inside the QQuickWidget gets focus. If this item can handle [TAB] key press, focus will change accordingly within the item, otherwise the next widget in the focus chain gets focus.

See also

Qt Quick Widgets Example QQuickView

class ResizeMode¶

This enum specifies how to resize the view.

Constant

Description

QQuickWidget.SizeViewToRootObject

The view resizes with the root item in the QML.

QQuickWidget.SizeRootObjectToView

The view will automatically resize the root item to the size of the view.

Constant	Description
QQuickWidget.SizeViewToRootObject	The view resizes with the root item in the QML.
QQuickWidget.SizeRootObjectToView	The view will automatically resize the root item to the size of the view.

class Status¶

Specifies the loading status of the QQuickWidget .

Constant

Description

QQuickWidget.Null

This QQuickWidget has no source set.

QQuickWidget.Ready

This QQuickWidget has loaded and created the QML component.

QQuickWidget.Loading

This QQuickWidget is loading network data.

QQuickWidget.Error

One or more errors occurred. Call errors() to retrieve a list of errors.

Constant	Description
QQuickWidget.Null	This `QQuickWidget` has no source set.
QQuickWidget.Ready	This `QQuickWidget` has loaded and created the QML component.
QQuickWidget.Loading	This `QQuickWidget` is loading network data.
QQuickWidget.Error	One or more errors occurred. Call `errors()` to retrieve a list of errors.

Note

Properties can be used directly when from __feature__ import true_property is used or via accessor functions otherwise.

property resizeModeᅟ: QQuickWidget.ResizeMode¶

This property Determines whether the view should resize the window contents..

If this property is set to SizeViewToRootObject (the default), the view resizes to the size of the root item in the QML.

If this property is set to SizeRootObjectToView , the view will automatically resize the root item to the size of the view.

Regardless of this property, the sizeHint of the view is the initial size of the root item. Note though that since QML may load dynamically, that size may change.

See also

initialSize()

Access functions:

resizeMode()
setResizeMode()

property sourceᅟ: QUrl¶

This property holds The URL of the source of the QML component..

Ensure that the URL provided is full and correct, in particular, use QUrl::fromLocalFile() when loading a file from the local filesystem.

Note

Setting a source URL will result in the QML component being instantiated, even if the URL is unchanged from the current value.

Access functions:

source()
setSource()

property statusᅟ: QQuickWidget.Status¶

The component’s current status .

Access functions:

status()
Signal statusChanged()

__init__([parent=None])¶

Parameters:: parent – QWidget

Constructs a QQuickWidget with a default QML engine as a child of parent.

The default value of parent is nullptr.

__init__(engine, parent)

Parameters:

engine – QQmlEngine
parent – QWidget

Constructs a QQuickWidget with the given QML engine as a child of parent.

Note

The QQuickWidget does not take ownership of the given engine object; it is the caller’s responsibility to destroy the engine. If the engine is deleted before the view, status() will return Error .

__init__(source[, parent=None])

Parameters:

source – QUrl
parent – QWidget

Constructs a QQuickWidget with a default QML engine and the given QML source as a child of parent.

The default value of parent is nullptr.

engine()¶

Return type:: QQmlEngine

Returns a pointer to the QQmlEngine used for instantiating QML Components.

errors()¶

Return type:: .list of QQmlError

Return the list of errors that occurred during the last compile or create operation. When the status is not Error , an empty list is returned.

See also

status

format()¶

Return type:: QSurfaceFormat

Returns the actual surface format.

If the widget has not yet been shown, the requested format is returned.

See also

setFormat()

grabFramebuffer()¶

Return type:: QImage

Renders a frame and reads it back into an image.

Note

This is a potentially expensive operation.

initialSize()¶

Return type:: QSize

Returns the initial size of the root object.

If resizeMode is SizeRootObjectToView , the root object will be resized to the size of the view. This function returns the size of the root object before it was resized.

quickWindow()¶

Return type:: QQuickWindow

Returns the offscreen QQuickWindow which is used by this widget to drive the Qt Quick rendering. This is useful if you want to use QQuickWindow APIs that are not currently exposed by QQuickWidget , for instance connecting to the beforeRendering() signal in order to draw native OpenGL content below Qt Quick’s own rendering.

Warning

Use the return value of this function with caution. In particular, do not ever attempt to show the QQuickWindow , and be very careful when using other QWindow-only APIs.

Warning

The offscreen window may be deleted (and recreated) during the life time of the QQuickWidget , particularly when the widget is moved to another QQuickWindow . If you need to know when the window has been replaced, connect to its destroyed() signal.

resizeMode()¶

Return type:: ResizeMode