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QQmlApplicationEngine 类

QQmlApplicationEngine 提供从单个 QML 文件加载应用程序的便捷方式。 更多...

头： #include <QQmlApplicationEngine>
CMake: find_package(Qt6 REQUIRED COMPONENTS Qml)
target_link_libraries(mytarget PRIVATE Qt6::Qml)
qmake: QT += qml
继承： QQmlEngine

公共函数

QQmlApplicationEngine (QObject * parent = nullptr)
QQmlApplicationEngine (const QUrl & url , QObject * parent = nullptr)
(从 6.5 起) QQmlApplicationEngine (QAnyStringView uri , QAnyStringView typeName , QObject * parent = nullptr)
QQmlApplicationEngine (const QString & filePath , QObject * parent = nullptr)
virtual ~QQmlApplicationEngine () override
QList<QObject *> rootObjects () const

公共槽

void load (const QUrl & url )
void load (const QString & filePath )
void loadData (const QByteArray & data , const QUrl & url = QUrl())
(从 6.5 起) void loadFromModule (QAnyStringView uri , QAnyStringView typeName )
(从 6.0 起) void setExtraFileSelectors (const QStringList & extraFileSelectors )
void setInitialProperties (const QVariantMap & initialProperties )

信号

void objectCreated (QObject * object , const QUrl & url )
(从 6.4 起) void objectCreationFailed (const QUrl & url )

详细描述

此类组合 QQmlEngine and QQmlComponent 提供加载单个 QML 文件的便捷方式。它还向 QML 暴露某些中心应用程序功能，C++/QML 混合应用程序通常从 C++ 进行控制。

它可以像这样使用： 

#include <QGuiApplication>
#include <QQmlApplicationEngine>
int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine("main.qml");
    return app.exec();
}

不像 QQuickView ，QQmlApplicationEngine 不会自动创建根窗口。若正使用来自 Qt Quick 的视觉项，需要将它们放入 Window .

还可以使用 QCoreApplication 采用 QQmlApplicationEngine，若未使用任何 QML 模块要求 QGuiApplication (譬如 QtQuick ).

配置列表的改变从默认 QQmlEngine :

  • 连接 Qt. quit () 到 QCoreApplication::quit ()
  • 自动从主 QML 文件相邻 i18n 目录下加载翻译文件。
    • 翻译文件必须拥有 qml_ 前缀，如 qml_ja_JP.qm。
  • 翻译被重新加载当 QJSEngine::uiLanguage / Qt.uiLanguage 特性改变。
  • 自动设置孵化控制器，若场景包含 QQuickWindow .
  • 自动设置 QQmlFileSelector 作为 URL 拦截器，将文件选择器应用于所有 QML 文件和资产。

可以进一步微调引擎行为，通过使用继承的方法从 QQmlEngine .

成员函数文档编制

QQmlApplicationEngine:: QQmlApplicationEngine ( QObject * parent = nullptr)

Create a new QQmlApplicationEngine with the given parent . You will have to call load () later in order to load a QML file.

QQmlApplicationEngine:: QQmlApplicationEngine (const QUrl & url , QObject * parent = nullptr)

Create a new QQmlApplicationEngine and loads the QML file at the given url . This is provided as a convenience, and is the same as using the empty constructor and calling load afterwards.

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

Create a new QQmlApplicationEngine and loads the QML type specified by uri and typeName This is provided as a convenience, and is the same as using the empty constructor and calling loadFromModule afterwards.

该函数在 Qt 6.5 引入。

QQmlApplicationEngine:: QQmlApplicationEngine (const QString & filePath , QObject * parent = nullptr)

Create a new QQmlApplicationEngine and loads the QML file at the given filePath , which must be a local file path. If a relative path is given then it will be interpreted as relative to the working directory of the application.

This is provided as a convenience, and is the same as using the empty constructor and calling load afterwards.

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

销毁 QQmlApplicationEngine and all QML objects it loaded.

[slot] void QQmlApplicationEngine:: load (const QUrl & url )

Loads the root QML file located at url . The object tree defined by the file is created immediately for local file urls. Remote urls are loaded asynchronously, listen to the objectCreated signal to determine when the object tree is ready.

If an error occurs, the objectCreated signal is emitted with a null pointer as parameter and error messages are printed with qWarning .

[slot] void QQmlApplicationEngine:: load (const QString & filePath )

Loads the root QML file located at filePath . filePath must be a path to a local file. If filePath is a relative path, it is taken as relative to the application's working directory. The object tree defined by the file is instantiated immediately.

若出现错误，打印错误消息采用 qWarning .

[slot] void QQmlApplicationEngine:: loadData (const QByteArray & data , const QUrl & url = QUrl())

Loads the QML given in data . The object tree defined by data is instantiated immediately.

若 url is specified it is used as the base url of the component. This affects relative paths within the data and error messages.

若出现错误，打印错误消息采用 qWarning .

[slot, since 6.5] void QQmlApplicationEngine:: loadFromModule ( QAnyStringView uri , QAnyStringView typeName )

Loads the QML type typeName from the module specified by uri . If the type originates from a QML file located at a remote url, the type will be loaded asynchronously. Listen to the objectCreated signal to determine when the object tree is ready.

If an error occurs, the objectCreated signal is emitted with a null pointer as parameter and error messages are printed with qWarning . 

QQmlApplicationEngine engine;
engine.loadFromModule("QtQuick", "Rectangle");

注意： The module identified by uri is searched in the import 路径 , in the same way as if you were doing import uri inside a QML file. If the module cannot be located there, this function will fail.

该函数在 Qt 6.5 引入。

另请参阅 QQmlComponent::loadFromModule .

[signal] void QQmlApplicationEngine:: objectCreated ( QObject * object , const QUrl & url )

This signal is emitted when an object finishes loading. If loading was successful, object contains a pointer to the loaded object, otherwise the pointer is NULL.

The url to the component the object came from is also provided.

注意： If the path to the component was provided as a QString containing a relative path, the url will contain a fully resolved path to the file.

[signal, since 6.4] void QQmlApplicationEngine:: objectCreationFailed (const QUrl & url )

This signal is emitted when loading finishes because an error occurred.

The url to the component that failed to load is provided as an argument. 

QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
// exit on error
QObject::connect(&engine, &QQmlApplicationEngine::objectCreationFailed,
    &app, []() { QCoreApplication::exit(-1); }, Qt::QueuedConnection);
engine.load(QUrl());
return app.exec();

注意： If the path to the component was provided as a QString containing a relative path, the url will contain a fully resolved path to the file.

另请参阅 QQmlApplicationEngine::objectCreated , which will be emitted in addition to this signal (even though creation failed).

该函数在 Qt 6.4 引入。

QList < QObject *> QQmlApplicationEngine:: rootObjects () const

Returns a list of all the root objects instantiated by the QQmlApplicationEngine . This will only contain objects loaded via load () or a convenience constructor.

注意： In Qt versions prior to 5.9, this function is marked as non- const .

[slot, since 6.0] void QQmlApplicationEngine:: setExtraFileSelectors (const QStringList & extraFileSelectors )

设置 extraFileSelectors to be passed to the internal QQmlFileSelector used for resolving URLs to local files. The extraFileSelectors are applied when the first QML file is loaded. Setting them afterwards has no effect.

该函数在 Qt 6.0 引入。

另请参阅 QQmlFileSelector and QFileSelector::setExtraSelectors .

[slot] void QQmlApplicationEngine:: setInitialProperties (const QVariantMap & initialProperties )

设置 initialProperties with which the QML component gets initialized after it gets loaded. 

QQmlApplicationEngine engine;
EventDatabase eventDatabase;
EventMonitor eventMonitor;
engine.setInitialProperties({
    { "eventDatabase", QVariant::fromValue(&eventDatabase) },
    { "eventMonitor", QVariant::fromValue(&eventMonitor) }
});

另请参阅 QQmlComponent::setInitialProperties , QQmlApplicationEngine::load ，和 QQmlApplicationEngine::loadData .

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