QQmlComponent Class

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 QQmlComponent::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 QQmlComponent::statusChanged() signal and otherwise calls the continueLoading() method directly. Note that QQmlComponent::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, &QQmlComponent::statusChanged,
                         this, &MyApplication::continueLoading);
    } else {
        continueLoading();
    }
}

void MyApplication::continueLoading()
{
    if (component->isError()) {
        qWarning() << component->errors();
    } else {
        QObject *myObject = component->create();
    }
}

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

Specifies the loading status of the QQmlComponent.

The progress of loading the component, from 0.0 (nothing loaded) to 1.0 (finished).

Access functions:

• qreal progress() const

Notifier signal:

• void progressChanged(qreal progress)

The component's current status.

Access functions:

• status() const

Notifier signal:

• void statusChanged( status)

The component URL. This is the URL passed to either the constructor, or the loadUrl(), or setData() methods.

Access functions:

• url() const

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

Create a QQmlComponent from the given fileName and give it the specified parent and engine.

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Create a QQmlComponent from the given fileName and give it the specified parent and engine. If mode is Asynchronous, the component will be loaded and compiled asynchronously.

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Create a QQmlComponent from the given url and give it the specified parent and engine.

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

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

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Create a QQmlComponent from the given url and give it the specified parent and engine. If mode is Asynchronous, the component will be loaded and compiled asynchronously.

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

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

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Destruct the QQmlComponent.

Create an object instance from this component, within the specified context. Returns nullptr if creation failed.

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, QQmlParserStatus::componentComplete() is called on objects.

QQmlComponent::beginCreate() differs from QQmlComponent::create() in that it only performs step 1. QQmlComponent::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.

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

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

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Create an object instance from this component, within the specified context. Returns nullptr if creation failed.

If context is nullptr (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 QQuickItem::setParentItem(). See Concepts - Visual Parent in Qt Quick for more details.

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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 nullptr (by 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 QQmlIncubator::IncubationMode is QQmlIncubator::AsynchronousIfNested, this object will also be created asynchronously. If forContext is nullptr (by default), the context will be used for this decision.

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

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Create an object instance of this component, within the specified context, and initialize its top-level properties with initialProperties.

If any of the initialProperties cannot be set, isError() will return true, and the errors() function can be used to get detailed information about the error(s).

This function was introduced in Qt 5.14.

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

Returns the QQmlEngine of this component.

This function was introduced in Qt 5.12.

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

Returns true if the component was created in a QML files that specifies pragma ComponentBehavior: Bound, otherwise returns false.

Returns true if status() == QQmlComponent::Error.

Returns true if status() == QQmlComponent::Loading.

Returns true if status() == QQmlComponent::Null.

Returns true if status() == QQmlComponent::Ready.

Load the QQmlComponent from the provided url.

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

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

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 QUrl::fromLocalFile() when loading a file from the local filesystem.

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

Emitted whenever the component's loading progress changes. progress will be the current progress between 0.0 (nothing loaded) and 1.0 (finished).

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.

Set top-level properties of the component.

This method provides advanced control over component instance creation. In general, programmers should use QQmlComponent::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.

This function was introduced in Qt 5.14.

Emitted whenever the component's status changes. status will be the new status.