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2. Qt 6.10.1
3. Qt QML
4. C++ 類
5. QQmlComponent

import QtQuick 2.0
Item {
    width: 200
    height: 200
}
					

QQmlEngine *engine = new QQmlEngine;
QQmlComponent component(engine, QUrl::fromLocalFile("main.qml"));
if (component.isError()) {
    qWarning() << "Failed to load main.qml:" << component.errors();
    return 1;
}
QObject *myObject = component.create();
if (component.isError()) {
    qWarning() << "Failed to create instance of main.qml:" << component.errors();
    return 1;
}
QQuickItem *item = qobject_cast<QQuickItem*>(myObject);
int width = item->width();  // width = 200
					

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);
}
					

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();
    }
}
					

成員類型文檔編製

enum QQmlComponent:: CompilationMode

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

enum QQmlComponent:: Status

指定正加載狀態為 QQmlComponent .

特性文檔編製

[read-only] progress : const qreal

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

訪問函數：

通知程序信號：

[read-only] status : const Status

組件的當前 status .

訪問函數：

通知程序信號：

[read-only] url : const QUrl

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

訪問函數：

成員函數文檔編製

QQmlComponent:: QQmlComponent ( QQmlEngine * engine , QObject * parent = nullptr)

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

QQmlComponent:: QQmlComponent ( QQmlEngine * engine , const QString & fileName , QObject * parent = nullptr)

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

另請參閱 loadUrl ().

QQmlComponent:: QQmlComponent ( QQmlEngine * engine , const QUrl & url , QObject * parent = nullptr)

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.

另請參閱 loadUrl ().

QQmlComponent:: QQmlComponent ( QQmlEngine * engine , const QString & fileName , QQmlComponent::CompilationMode mode , QObject * parent = nullptr)

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

另請參閱 loadUrl ().

QQmlComponent:: QQmlComponent ( QQmlEngine * engine , const QUrl & url , QQmlComponent::CompilationMode mode , QObject * parent = nullptr)

Create a QQmlComponent from the given url and give it the specified parent and engine 。若 mode is 異步 , 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.

另請參閱 loadUrl ().

[explicit, since 6.5] QQmlComponent:: QQmlComponent ( QQmlEngine * engine , QAnyStringView uri , QAnyStringView typeName , QObject * parent = nullptr)

Create a QQmlComponent from the given uri and typeName and give it the specified parent and engine . If possible, the component will be loaded synchronously.

這是重載函數。

該函數在 Qt 6.5 引入。

另請參閱 loadFromModule ().

[explicit, since 6.5] QQmlComponent:: QQmlComponent ( QQmlEngine * engine , QAnyStringView uri , QAnyStringView typeName , QQmlComponent::CompilationMode mode , QObject * parent = nullptr)

Create a QQmlComponent from the given uri and typeName and give it the specified parent and engine 。若 mode is 異步 , the component will be loaded and compiled asynchronously.

這是重載函數。

該函數在 Qt 6.5 引入。

另請參閱 loadFromModule ().

[override virtual noexcept] QQmlComponent:: ~QQmlComponent ()

Destruct the QQmlComponent .

[virtual] QObject *QQmlComponent:: beginCreate ( QQmlContext * context )

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

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

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

1. The object hierarchy is created, and constant values are assigned.
2. 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.

注意： The categorization of bindings into constant values and actual bindings is intentionally unspecified and may change between versions of Qt and depending on whether and how you are using qmlcachegen . You should not rely on any particular binding to be evaluated either before or after beginCreate() returns. For example a constant expression like MyType.EnumValue may be recognized as such at compile time or deferred to be executed as binding. The same holds for constant expressions like -(5) or "a" + " constant string" .

另請參閱 completeCreate () 和 QQmlEngine::ObjectOwnership .

[virtual] void QQmlComponent:: completeCreate ()

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.

另請參閱 beginCreate ().

[virtual] QObject *QQmlComponent:: create ( QQmlContext * context = nullptr)

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

若 context is nullptr (the default), it will create the instance in the 根上下文 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 ()。見 概念 - Qt Quick 中的視覺父級 瞭解更多細節。

另請參閱 QQmlEngine::ObjectOwnership .

void QQmlComponent:: create ( QQmlIncubator & incubator , QQmlContext * context = nullptr, QQmlContext * forContext = nullptr)

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

若 context is nullptr (the default), it will create the instance in the 根上下文 of the engine.

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 .

另請參閱 QQmlIncubator .

QObject *QQmlComponent:: createWithInitialProperties (const QVariantMap & initialProperties , QQmlContext * context = nullptr)

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, a warning is issued. If there are unset required properties, the object creation fails and returns nullptr ，在這種情況下 isError () 會返迴 true .

若 context is nullptr (the default), it will create the instance in the 根上下文 of the engine.

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

另請參閱 QQmlComponent::create .

QQmlContext *QQmlComponent:: creationContext () const

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

QQmlEngine *QQmlComponent:: engine () const

返迴 QQmlEngine of this component.

QList < QQmlError > QQmlComponent:: errors () const

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

[since 6.5] bool QQmlComponent:: isBound () const

Returns true if the component was created in a QML files that specifies pragma ComponentBehavior: Bound ，否則返迴 false。

該函數在 Qt 6.5 引入。

bool QQmlComponent:: isError () const

返迴 true 若 status () == QQmlComponent::Error .

bool QQmlComponent:: isLoading () const

返迴 true 若 status () == QQmlComponent::Loading .

bool QQmlComponent:: isNull () const

返迴 true 若 status () == QQmlComponent::Null .

bool QQmlComponent:: isReady () const

返迴 true 若 status () == QQmlComponent::Ready .

[slot, since 6.5] void QQmlComponent:: loadFromModule ( QAnyStringView uri , QAnyStringView typeName , QQmlComponent::CompilationMode mode = PreferSynchronous)

加載 QQmlComponent for typeName in the module uri . If the type is implemented via a QML file, mode is used to load it. Types backed by C++ are always loaded synchronously.

QQmlEngine engine;
QQmlComponent component(&engine);
component.loadFromModule("QtQuick", "Item");
// once the component is ready
std::unique_ptr<QObject> item(component.create());
Q_ASSERT(item->metaObject() == &QQuickItem::staticMetaObject);
			

該函數在 Qt 6.5 引入。

另請參閱 loadUrl ().

[slot] void QQmlComponent:: loadUrl (const QUrl & url )

加載 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.

注意： 此槽被重載。要連接到此槽：

// Connect using qOverload:
connect(qmlComponent, qOverload(&QQmlComponent::loadUrl),
        receiver, &ReceiverClass::slot);
// Or using a lambda:
connect(qmlComponent, qOverload(&QQmlComponent::loadUrl),
        this, [](const QUrl &url) { /* handle loadUrl */ });
			

更多範例和方式，見 連接到重載槽 .

[slot] void QQmlComponent:: loadUrl (const QUrl & url , QQmlComponent::CompilationMode mode )

加載 QQmlComponent from the provided url 。若 mode is 異步 , 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.

注意： 此槽被重載。要連接到此槽：

// Connect using qOverload:
connect(qmlComponent, qOverload(&QQmlComponent::loadUrl),
        receiver, &ReceiverClass::slot);
// Or using a lambda:
connect(qmlComponent, qOverload(&QQmlComponent::loadUrl),
        this, [](const QUrl &url, QQmlComponent::CompilationMode mode) { /* handle loadUrl */ });
			

更多範例和方式，見 連接到重載槽 .

[signal] void QQmlComponent:: progressChanged ( qreal progress )

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

注意： 通知程序信號對於特性 progress .

[slot] void QQmlComponent:: setData (const QByteArray & data , const QUrl & url )

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

警告： The new component will shadow any existing component of the same URL. You should not pass a URL of an existing component.

void QQmlComponent:: setInitialProperties ( QObject * object , const QVariantMap & properties )

Set top-level properties 的 object that was created from a QQmlComponent .

This method provides advanced control over component instance creation. In general, programmers should use QQmlComponent::createWithInitialProperties to create an object instance from 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 method does not allow setting initial nested properties directly. Instead, setting an initial value for value type properties with nested properties can be achieved by creating that value type, assigning its nested property and then passing the value type as an initial property of the object to be constructed.

For example, in order to set fond.bold, you can create a QFont , set its weight to bold and then pass the font as an initial property.

[signal] void QQmlComponent:: statusChanged ( QQmlComponent::Status status )

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

注意： 通知程序信號對於特性 status .