QDeclarativeExtensionPlugin Class
The QDeclarativeExtensionPlugin class provides an abstract base for custom QML extension plugins. More...
Header: | #include <QDeclarativeExtensionPlugin> |
qmake: | QT += declarative |
Since: | Qt 4.7 |
Inherits: |
Public Functions
QDeclarativeExtensionPlugin(QObject * parent = 0) |
Reimplemented Public Functions
virtual void | initializeEngine(QDeclarativeEngine * engine, const char * uri) |
virtual void | registerTypes(const char * uri) = 0 |
Detailed Description
The QDeclarativeExtensionPlugin class provides an abstract base for custom QML extension plugins.
QDeclarativeExtensionPlugin 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:
- Subclass QDeclarativeExtensionPlugin, implement registerTypes() method to register types using qmlRegisterType(), and export the class using the Q_PLUGIN_METADATA() macro
- Write an appropriate project file for the plugin
- Create a qmldir file to describe the plugin
QML extension plugins can be used to provide 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.
An example
Suppose there is a new TimeModel
C++ class that should be made available as a new QML element. It provides the current time through hour
and minute
properties, like this:
...
To make this class available as a QML type, create a plugin that registers this type with a specific module using qmlRegisterType(). For this example the plugin module will be named com.nokia.TimeExample
(as defined in the project file further below).
This registers the TimeModel
class with the 1.0 version of this plugin library, as a QML type called Time
. The Q_ASSERT statement ensures the module is imported correctly by any QML components that use this plugin.
The project file defines the project as a plugin library and specifies it should be built into the com/nokia/TimeExample
directory:
TEMPLATE = lib CONFIG += qt plugin QT += declarative DESTDIR = com/nokia/TimeExample TARGET = qmlqtimeexampleplugin ...
Finally, a qmldir file is required in the com/nokia/TimeExample
directory that describes the plugin. This directory includes a Clock.qml
file that should be bundled with the plugin, so it needs to be specified in the qmldir
file:
Once the project is built and installed, the new Time
element can be used by any QML component that imports the com.nokia.TimeExample
module:
The full source code is available in the plugins example.
The Tutorial: Writing QML extensions with C++ also contains a chapter on creating QML plugins.
See also QDeclarativeEngine::importPlugin() and How to Create Qt Plugins.
Member Function Documentation
QDeclarativeExtensionPlugin::QDeclarativeExtensionPlugin(QObject * parent = 0)
Constructs a QML extension plugin with the given parent.
Note that this constructor is invoked automatically by the plugin loader, so there is no need for calling it explicitly.
[virtual]
void QDeclarativeExtensionPlugin::initializeEngine(QDeclarativeEngine * engine, const char * uri)
Initializes the extension from the uri using the engine. Here an application plugin might, for example, expose some data or objects to QML, as context properties on the engine's root context.
[pure virtual]
void QDeclarativeExtensionPlugin::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.