QQmlComponent

The QQmlComponent class encapsulates a QML component definition. More

Inheritance diagram of PySide2.QtQml.QQmlComponent

Synopsis

Functions

Virtual functions

Slots

Signals

Detailed Description

Components are reusable, encapsulated QML types with well-defined interfaces.

A QQmlComponent instance can be created from a QML file. For example, if there is a main.qml file like this:

The following code loads this QML file as a component, creates an instance of this component using create() , and then queries the Item ‘s width value:

QQmlEngine *engine = new QQmlEngine;
QQmlComponent component(engine, QUrl::fromLocalFile("main.qml"));

QObject *myObject = component.create();
QQuickItem *item = qobject_cast<QQuickItem*>(myObject);
int width = item->width();  // width = 200

To create instances of a component in code where a QQmlEngine instance is not available, you can use qmlContext() or qmlEngine() . For example, in the scenario below, child items are being created within a QQuickItem subclass:

void MyCppItem::init()
{
    QQmlEngine *engine = qmlEngine(this);
    // Or:
    // QQmlEngine *engine = qmlContext(this)->engine();
    QQmlComponent component(engine, QUrl::fromLocalFile("MyItem.qml"));
    QQuickItem *childItem = qobject_cast<QQuickItem*>(component.create());
    childItem->setParentItem(this);
}

Note that these functions will return null when called inside the constructor of a QObject subclass, as the instance will not yet have a context nor engine.

Network Components

If the URL passed to QQmlComponent is a network resource, or if the QML document references a network resource, the QQmlComponent has to fetch the network data before it is able to create objects. In this case, the QQmlComponent will have a Loading status . An application will have to wait until the component is Ready before calling create() .

The following example shows how to load a QML file from a network resource. After creating the QQmlComponent , it tests whether the component is loading. If it is, it connects to the statusChanged() signal and otherwise calls the continueLoading() method directly. Note that isLoading() may be false for a network component if the component has been cached and is ready immediately.

MyApplication::MyApplication()
{
    // ...
    component = new QQmlComponent(engine, QUrl("http://www.example.com/main.qml"));
    if (component->isLoading())
        QObject::connect(component, SIGNAL(statusChanged(QQmlComponent::Status)),
                         this, SLOT(continueLoading()));
    else
        continueLoading();
}

void MyApplication::continueLoading()
{
    if (component->isError()) {
        qWarning() << component->errors();
    } else {
        QObject *myObject = component->create();
    }
}
class QQmlComponent([parent=None])

QQmlComponent(arg__1[, parent=None])

QQmlComponent(arg__1, fileName[, parent=None])

QQmlComponent(arg__1, fileName, mode[, parent=None])

QQmlComponent(arg__1, url[, parent=None])

QQmlComponent(arg__1, url, mode[, parent=None])

param parent

QObject

param url

QUrl

param arg__1

QQmlEngine

param fileName

unicode

param mode

CompilationMode

Create a QQmlComponent with no data and give it the specified engine and parent . Set the data with setData() .

PySide2.QtQml.QQmlComponent.CompilationMode

Specifies whether the QQmlComponent should load the component immediately, or asynchonously.

Constant

Description

QQmlComponent.PreferSynchronous

Prefer loading/compiling the component immediately, blocking the thread. This is not always possible; for example, remote URLs will always load asynchronously.

QQmlComponent.Asynchronous

Load/compile the component in a background thread.

PySide2.QtQml.QQmlComponent.Status

Specifies the loading status of the QQmlComponent .

Constant

Description

QQmlComponent.Null

This QQmlComponent has no data. Call loadUrl() or setData() to add QML content.

QQmlComponent.Ready

This QQmlComponent is ready and create() may be called.

QQmlComponent.Loading

This QQmlComponent is loading network data.

QQmlComponent.Error

An error has occurred. Call errors() to retrieve a list of errors .

PySide2.QtQml.QQmlComponent.beginCreate(arg__1)
Parameters

arg__1QQmlContext

Return type

QObject

This method provides advanced control over component instance creation. In general, programmers should use create() to create object instances.

Create an object instance from this component. Returns None if creation failed. publicContext specifies the context within which to create the object instance.

When QQmlComponent constructs an instance, it occurs in three steps:

  1. The object hierarchy is created, and constant values are assigned.

  2. Property bindings are evaluated for the first time.

  3. If applicable, componentComplete() is called on objects.

differs from create() in that it only performs step 1. completeCreate() must be called to complete steps 2 and 3.

This breaking point is sometimes useful when using attached properties to communicate information to an instantiated component, as it allows their initial values to be configured before property bindings take effect.

The ownership of the returned object instance is transferred to the caller.

See also

completeCreate() ObjectOwnership

PySide2.QtQml.QQmlComponent.completeCreate()

This method provides advanced control over component instance creation. In general, programmers should use create() to create a component.

This function completes the component creation begun with beginCreate() and must be called afterwards.

See also

beginCreate()

PySide2.QtQml.QQmlComponent.create([context=None])
Parameters

contextQQmlContext

Return type

QObject

Create an object instance from this component. Returns None if creation failed. context specifies the context within which to create the object instance.

If context is None (the default), it will create the instance in the root context of the engine.

The ownership of the returned object instance is transferred to the caller.

If the object being created from this component is a visual item, it must have a visual parent, which can be set by calling setParentItem() . See Concepts - Visual Parent in Qt Quick for more details.

See also

ObjectOwnership

PySide2.QtQml.QQmlComponent.create(arg__1[, context=None[, forContext=None]])
Parameters

Create an object instance from this component using the provided incubator . context specifies the context within which to create the object instance.

If context is 0 (the default), it will create the instance in the engine’s root context .

forContext specifies a context that this object creation depends upon. If the forContext is being created asynchronously, and the IncubationMode is AsynchronousIfNested , this object will also be created asynchronously. If forContext is 0 (the default), the context will be used for this decision.

The created object and its creation status are available via the incubator .

See also

QQmlIncubator

PySide2.QtQml.QQmlComponent.createWithInitialProperties(initialProperties[, context=None])
Parameters
Return type

QObject

Create an object instance of this component, and initialize its toplevel properties with initialProperties . context specifies the context where the object instance is to be created.

See also

create

PySide2.QtQml.QQmlComponent.creationContext()
Return type

QQmlContext

Returns the QQmlContext the component was created in. This is only valid for components created directly from QML.

PySide2.QtQml.QQmlComponent.engine()
Return type

QQmlEngine

Returns the QQmlEngine of this component.

PySide2.QtQml.QQmlComponent.errorString()
Return type

unicode

errorString is only meant as a way to get the errors in script

PySide2.QtQml.QQmlComponent.errors()
Return type

Returns the list of errors that occurred during the last compile or create operation. An empty list is returned if isError() is not set.

PySide2.QtQml.QQmlComponent.isError()
Return type

bool

Returns true if status() == Error .

PySide2.QtQml.QQmlComponent.isLoading()
Return type

bool

Returns true if status() == Loading .

PySide2.QtQml.QQmlComponent.isNull()
Return type

bool

Returns true if status() == Null .

PySide2.QtQml.QQmlComponent.isReady()
Return type

bool

Returns true if status() == Ready .

PySide2.QtQml.QQmlComponent.loadUrl(url)
Parameters

urlQUrl

Load the QQmlComponent from the provided url .

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

Relative paths will be resolved against baseUrl() , which is the current working directory unless specified.

PySide2.QtQml.QQmlComponent.loadUrl(url, mode)
Parameters

Load the QQmlComponent from the provided url . If mode is Asynchronous , the component will be loaded and compiled asynchronously.

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

Relative paths will be resolved against baseUrl() , which is the current working directory unless specified.

PySide2.QtQml.QQmlComponent.progress()
Return type

qreal

PySide2.QtQml.QQmlComponent.progressChanged(arg__1)
Parameters

arg__1qreal

PySide2.QtQml.QQmlComponent.setData(arg__1, baseUrl)
Parameters
  • arg__1QByteArray

  • baseUrlQUrl

Sets the QQmlComponent to use the given QML data . If url is provided, it is used to set the component name and to provide a base path for items resolved by this component.

PySide2.QtQml.QQmlComponent.setInitialProperties(component, properties)
Parameters
  • componentQObject

  • properties

Set toplevel properties of the component .

This method provides advanced control over component instance creation. In general, programmers should use createWithInitialProperties to create a component.

Use this method after beginCreate and before completeCreate has been called. If a provided property does not exist, a warning is issued.

PySide2.QtQml.QQmlComponent.status()
Return type

Status

PySide2.QtQml.QQmlComponent.statusChanged(arg__1)
Parameters

arg__1Status

PySide2.QtQml.QQmlComponent.url()
Return type

QUrl