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<QtPlugin> - Macros for Defining Plugins

The <QtPlugin> header files defines macros for defining plugins. More...

Macros

• Q_DECLARE_INTERFACE ( ClassName, Identifier )
• Q_EXPORT_PLUGIN2 ( PluginName, ClassName )
• Q_IMPORT_PLUGIN ( PluginName )

Detailed Description

The <QtPlugin> header files defines macros for defining plugins.

See also How to Create Qt Plugins.

Macro Documentation

Q_DECLARE_INTERFACE ( ClassName, Identifier )

This macro associates the given Identifier (a string literal) to the interface class called ClassName. The Identifier must be unique. For example:

    Q_DECLARE_INTERFACE(BrushInterface,
                        "com.trolltech.PlugAndPaint.BrushInterface/1.0")

This macro is normally used right after the class definition for ClassName, in a header file. See the Plug & Paint example for details.

If you want to use Q_DECLARE_INTERFACE with interface classes declared in a namespace then you have to make sure the Q_DECLARE_INTERFACE is not inside a namespace though. For example:

    namespace Foo
    {
        struct MyInterface { ... };
    }
    Q_DECLARE_INTERFACE(Foo::MyInterface, "org.examples.MyInterface")

See also Q_INTERFACES(), Q_EXPORT_PLUGIN2(), and How to Create Qt Plugins.

Q_EXPORT_PLUGIN2 ( PluginName, ClassName )

This macro exports the plugin class ClassName with the name PluginName. There should be exactly one occurrence of this macro in a Qt plugin's source code (in an implementation file).

Example:

    Q_EXPORT_PLUGIN2(pnp_extrafilters, ExtraFiltersPlugin)

See the Plug & Paint example for details.

This function was introduced in Qt 4.1.

See also Q_DECLARE_INTERFACE() and How to Create Qt Plugins.

Q_IMPORT_PLUGIN ( PluginName )

This macro imports the plugin named PluginName. Inserting this macro into your application's source code will allow you to make use of a static plugin.

Example:

    Q_IMPORT_PLUGIN(qjpeg)

Static plugins must also be included by the linker when your application is built. For Qt's predefined plugins, you can use the QTPLUGIN to add the required plugins to your build. For example:

    TEMPLATE      = app
    QTPLUGIN     += qjpeg qgif qmng    # image formats

See also Static Plugins, How to Create Qt Plugins, and Using qmake.