QQmlComponent¶
The
QQmlComponent
class encapsulates a QML component definition. More…
Synopsis¶
Functions¶
Virtual functions¶
def
beginCreate
(arg__1)def
completeCreate
()def
create
([context=None])
Signals¶
def
progressChanged
(arg__1)def
statusChanged
(arg__1)
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 amain.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 = 200To create instances of a component in code where a
QQmlEngine
instance is not available, you can useqmlContext()
orqmlEngine()
. For example, in the scenario below, child items are being created within aQQuickItem
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 aQObject
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, theQQmlComponent
has to fetch the network data before it is able to create objects. In this case, theQQmlComponent
will have aLoading
status
. An application will have to wait until the component isReady
before callingcreate()
.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 thestatusChanged()
signal and otherwise calls thecontinueLoading()
method directly. Note thatisLoading()
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
- param fileName
unicode
- param mode
CompilationMode
Create a
QQmlComponent
with no data and give it the specifiedengine
andparent
. Set the data withsetData()
.
-
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. CallloadUrl()
orsetData()
to add QML content.QQmlComponent.Ready
This
QQmlComponent
is ready andcreate()
may be called.QQmlComponent.Loading
This
QQmlComponent
is loading network data.QQmlComponent.Error
An error has occurred. Call
errors()
to retrieve a list oferrors
.
-
PySide2.QtQml.QQmlComponent.
beginCreate
(arg__1)¶ - Parameters
arg__1 –
QQmlContext
- 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:The object hierarchy is created, and constant values are assigned.
Property bindings are evaluated for the first time.
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
-
PySide2.QtQml.QQmlComponent.
create
([context=None])¶ - Parameters
context –
QQmlContext
- 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
isNone
(the default), it will create the instance in theroot 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
arg__1 –
QQmlIncubator
context –
QQmlContext
forContext –
QQmlContext
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’sroot context
.forContext
specifies a context that this object creation depends upon. If theforContext
is being created asynchronously, and theIncubationMode
isAsynchronousIfNested
, this object will also be created asynchronously. IfforContext
is 0 (the default), thecontext
will be used for this decision.The created object and its creation status are available via the
incubator
.See also
-
PySide2.QtQml.QQmlComponent.
creationContext
()¶ - Return type
Returns the
QQmlContext
the component was created in. This is only valid for components created directly from QML.
-
PySide2.QtQml.QQmlComponent.
engine
()¶ - Return type
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.
loadUrl
(url)¶ - Parameters
url –
QUrl
Load the
QQmlComponent
from the providedurl
.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
url –
QUrl
mode –
CompilationMode
Load the
QQmlComponent
from the providedurl
. Ifmode
isAsynchronous
, 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__1 –
qreal
-
PySide2.QtQml.QQmlComponent.
setData
(arg__1, baseUrl)¶ - Parameters
arg__1 –
QByteArray
baseUrl –
QUrl
Sets the
QQmlComponent
to use the given QMLdata
. Ifurl
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.
url
()¶ - Return type
QUrl
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