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# QDeclarativeComponent Class Reference
[QtDeclarative module]

The QDeclarativeComponent class encapsulates a QML component definition. More...

Inherits QObject.

### Types

- enum Status { Null, Ready, Loading, Error }

### Methods

- __init__ (self, QDeclarativeEngine, QObject parent = None)
- __init__ (self, QDeclarativeEngine, QString fileName, QObject parent = None)
- __init__ (self, QDeclarativeEngine, QUrl url, QObject parent = None)
- QObject beginCreate (self, QDeclarativeContext)
- completeCreate (self)
- QObject create (self, QDeclarativeContext context = None)
- QDeclarativeContext creationContext (self)
- list-of-QDeclarativeError errors (self)
- bool isError (self)
- bool isLoading (self)
- bool isNull (self)
- bool isReady (self)
- loadUrl (self, QUrl url)
- float progress (self)
- setData (self, QByteArray, QUrl baseUrl)
- Status status (self)
- QUrl url (self)

### Qt Signals

- void progressChanged (qreal)
- void statusChanged (QDeclarativeComponent::Status)

## Detailed Description

The QDeclarativeComponent class encapsulates a QML component definition.

Components are reusable, encapsulated QML elements with well-defined interfaces. They are often defined in Component Files.

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

     import QtQuick 1.0

     Item {
         width: 200
         height: 200
     }

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:

     QDeclarativeEngine *engine = new QDeclarativeEngine;
     QDeclarativeComponent component(engine, QUrl.fromLocalFile("main.qml"));

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

#### Network Components

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

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

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

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

## Type Documentation

### QDeclarativeComponent.Status

Specifies the loading status of the QDeclarativeComponent.

Constant | Value | Description
--- | --- | ---
`QDeclarativeComponent.Null` | `0` | This QDeclarativeComponent has no data. Call loadUrl() or setData() to add QML content.
`QDeclarativeComponent.Ready` | `1` | This QDeclarativeComponent is ready and create() may be called.
`QDeclarativeComponent.Loading` | `2` | This QDeclarativeComponent is loading network data.
`QDeclarativeComponent.Error` | `3` | An error has occurred. Call errors() to retrieve a list of {QDeclarativeError}{errors}.

## Method Documentation

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

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

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

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

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

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

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

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

See also loadUrl().

### QObject QDeclarativeComponent.beginCreate (self, QDeclarativeContext)

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

Create an object instance from this component. Returns 0 if creation failed. context specifies the context within which to create the object instance.

When QDeclarativeComponent 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 the first time.
3. If applicable, QDeclarativeParserStatus.componentComplete() is called on objects.

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

### QDeclarativeComponent.completeCreate (self)

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

Complete a component creation begin with QDeclarativeComponent.beginCreate().

### QObject QDeclarativeComponent.create (self, QDeclarativeContext context = None)

Create an object instance from this component. Returns 0 if creation failed. 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.

### QDeclarativeContext QDeclarativeComponent.creationContext (self)

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

### list-of-QDeclarativeError QDeclarativeComponent.errors (self)

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

### bool QDeclarativeComponent.isError (self)

Returns true if status() == QDeclarativeComponent.Error.

### bool QDeclarativeComponent.isLoading (self)

Returns true if status() == QDeclarativeComponent.Loading.

### bool QDeclarativeComponent.isNull (self)

Returns true if status() == QDeclarativeComponent.Null.

### bool QDeclarativeComponent.isReady (self)

Returns true if status() == QDeclarativeComponent.Ready.

### QDeclarativeComponent.loadUrl (self, QUrl url)

Load the QDeclarativeComponent 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.

### float QDeclarativeComponent.progress (self)

### QDeclarativeComponent.setData (self, QByteArray, QUrl baseUrl)

Sets the QDeclarativeComponent 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.

### Status QDeclarativeComponent.status (self)

### QUrl QDeclarativeComponent.url (self)

## Qt Signal Documentation

### void progressChanged (qreal)

This is the default overload of this signal.

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

### void statusChanged (QDeclarativeComponent::Status)

This is the default overload of this signal.

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