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公共函数
重实现公共函数
静态公共成员
详细描述
TimeExample QML extension plugin
Project settings for the plugin
在 qmldir 下的插件定义

QQmlExtensionPlugin Class

The QQmlExtensionPlugin class provides an abstract base for custom QML extension plugins. 更多...

头：	#include <QQmlExtensionPlugin>
qmake:	QT += qml
Since:	Qt 5.0
继承：	QObject

公共函数

	QQmlExtensionPlugin (QObject * parent = nullptr)
QUrl	baseUrl () const

重实现公共函数

virtual void	initializeEngine (QQmlEngine * engine , const char * uri ) override
virtual void	registerTypes (const char * uri ) override = 0

31 公共函数继承自 QObject

静态公共成员

const QMetaObject

staticMetaObject

9 静态公共成员继承自 QObject

额外继承成员

1 特性继承自 QObject
1 公共槽继承自 QObject
2 信号继承自 QObject
9 保护函数继承自 QObject

详细描述

The QQmlExtensionPlugin class provides an abstract base for custom QML extension plugins.

QQmlExtensionPlugin is a plugin interface that makes it possible to create QML extensions that can be loaded dynamically into QML applications. These extensions allow custom QML types to be made available to the QML engine.

To write a QML extension plugin:

子类 QQmlExtensionPlugin
- 使用 Q_PLUGIN_METADATA () macro to register the plugin with the Qt meta object system
- Override the registerTypes() method and call qmlRegisterType () to register the types to be exported by the plugin
Write a project file for the plugin
创建 qmldir 文件 to describe the plugin

QML extension plugins are for either application-specific or library-like plugins. Library plugins should limit themselves to registering types, as any manipulation of the engine's root context may cause conflicts or other issues in the library user's code.

TimeExample QML extension plugin

Suppose there is a new TimeModel C++ class that should be made available as a new QML type. It provides the current time through hour and minute 特性。

class TimeModel : public QObject
{
    Q_OBJECT
    Q_PROPERTY(int hour READ hour NOTIFY timeChanged)
    Q_PROPERTY(int minute READ minute NOTIFY timeChanged)
    ...

To make this type available, we create a plugin class named QExampleQmlPlugin which is a subclass of QQmlExtensionPlugin . It overrides the registerTypes() method in order to register the TimeModel type using qmlRegisterType (). It also uses the Q_PLUGIN_METADATA () macro in the class definition to register the plugin with the Qt meta object system using a unique identifier for the plugin.

class QExampleQmlPlugin : public QQmlExtensionPlugin
{
    Q_OBJECT
    Q_PLUGIN_METADATA(IID QQmlExtensionInterface_iid)
public:
    void registerTypes(const char *uri) override
    {
        Q_ASSERT(uri == QLatin1String("TimeExample"));
        qmlRegisterType<TimeModel>(uri, 1, 0, "Time");
    }
};

This registers the TimeModel class with version 1.0 of this plugin library, as a QML type called 时间 。 Q_ASSERT () macro can ensure the type namespace is imported correctly by any QML components that use this plugin. The 从 C++ 定义 QML 类型 article has more information about registering C++ types into the runtime.

Project settings for the plugin

Additionally, the project file ( .pro ) defines the project as a plugin library, specifies it should be built into the imports/TimeExample directory, and registers the plugin target name and various other details:

TEMPLATE = lib
CONFIG += qt plugin
QT += qml
DESTDIR = imports/TimeExample
TARGET = qmlqtimeexampleplugin
SOURCES += qexampleqmlplugin.cpp

在 qmldir 下的插件定义

Finally, a qmldir 文件 is required in the imports/TimeExample directory to describe the plugin and the types that it exports. The plugin includes a Clock.qml file along with the qmlqtimeexampleplugin that is built by the project (as shown above in the .pro file) so both of these need to be specified in the qmldir 文件：

module TimeExample
Clock 1.0 Clock.qml
plugin qmlqtimeexampleplugin

To make things easier for this example, the TimeExample source directory is in imports/TimeExample , and we build in-source . However, the structure of the source directory is not so important, as the qmldir file can specify paths to installed QML files.

What is important is the name of the directory that the qmldir is installed into. When the user imports our module, the QML engine uses the 模块标识符 ( TimeExample ) to find the plugin, and so the directory in which it is installed must match the module identifier.

Once the project is built and installed, the new 时间 component is accessible by any QML component that imports the TimeExample 模块

import TimeExample 1.0 // import types from the plugin
Clock { // this class is defined in QML (imports/TimeExample/Clock.qml)
    Time { // this class is defined in C++ (plugin.cpp)
        id: time
    }
    hours: time.hour
    minutes: time.minute
}

The full source code is available in the plugins example .

The 采用 C++ 编写 QML 扩展 tutorial also contains a chapter on creating QML plugins.

另请参阅 QQmlEngine::importPlugin () 和如何创建 Qt 插件 .

成员函数文档编制

QQmlExtensionPlugin:: QQmlExtensionPlugin ( QObject * parent = nullptr)

Constructs a QML extension plugin with the given parent .

Note that this constructor is invoked automatically by the Q_PLUGIN_METADATA () macro, so there is no need for calling it explicitly.

QUrl QQmlExtensionPlugin:: baseUrl () const

Returns the URL of the directory from which the extension is loaded.

This is useful when the plugin also needs to load QML files or other assets from the same directory.

该函数在 Qt 5.1 引入。

`[override virtual]` void QQmlExtensionPlugin:: initializeEngine ( QQmlEngine * engine , const char * uri )

Initializes the extension from the uri 使用 engine . Here an application plugin might, for example, expose some data or objects to QML, as context properties on the engine's root context.

`[override pure virtual]` void QQmlExtensionPlugin:: registerTypes (const char * uri )

Registers the QML types in the given uri . Subclasses should implement this to call qmlRegisterType () for all types which are provided by the extension plugin.

The uri is an identifier for the plugin generated by the QML engine based on the name and path of the extension's plugin library.

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