Extension Interfaces and Plugins

From KDevelop

The idea behind extension interfaces is to provide following features:

To allow plugins to expose their functionality via abstract interfaces and at the same time do not care about BC and do not force other plugins to link with them. Documentation plugin would be a good example of non-core but still sometimes useful functionality that might be exported via IDocumentation extension interface with methods like lookupInDocumentation(const QString &) and others. KDevelop4's outputview plugin with IOutputView interface is also a good and actually working example of such use-case.
To have implementations of important functionality not in a shell, but in plugins. Good examples are buildsystem managers, builders and language supports in KDevelop4. When a project is opened, a buildsystem manager plugin (that implements either IBuildSystemManager interface or IProjectFileManager) is looked for by the shell an loaded.
To forget about BC issues of dependent plugins. In case the plugin has something new to expose, the new version of extension interface has to be defined. All other plugins will either continue using old interface or ask for the new one.

The extension interfaces framework is implemented with QExtensionManager and Co. See the Qt documentation for reference.

1 To declare extension interface
2 To implement extension interface
3 To load a plugin that supports extension interface
4 To set a dependency between plugins

[edit] To declare extension interface

Create an abstract class
Include <iextension.h>
Add following macros to the header file with a class (if you use a namespace):

       KDEV_DECLARE_EXTENSION_INTERFACE_NS( KDevelop, IMyInterface, "org.kdevelop.IMyInterface")
       Q_DECLARE_INTERFACE( KDevelop::IMyInterface, "org.kdevelop.IMyInterface" )

or use (when the interface is not in a namespace)

       KDEV_DECLARE_EXTENSION_INTERFACE( IMyInterface, "org.kdevelop.IMyInterface" )
       Q_DECLARE_INTERFACE( IMyInterface, "org.kdevelop.IMyInterface" )

[edit] To implement extension interface

Create a plugin as usual
Subclass it from your interface
Use Q_INTERFACES macro in class declaration
use KDEV_USE_EXTENSION_INTERFACE macro in the constructor of the plugin

       KDEV_USE_EXTENSION_INTERFACE( IMyInterface )

declare in plugin's .desktop file:

       X-KDevelop-Interfaces=IMyInterface

Code Example:

       class MyPlugin: public KDevelop::IPlugin, public KDevelop::IMyInterface {
           Q_OBJECT
           Q_INTERFACES(KDevelop::IMyInterface)
       public:
           MyPlugin( QObject* parent ) : IPlugin( parent )
           {
               KDEV_USE_EXTENSION_INTERFACE( KDevelop::IMyInterface )
           }
       };

[edit] To load a plugin that supports extension interface

Use IPluginController::pluginForExtension() method if you have only one possible plugin implementing the extension interface
Or use IPluginController::allPluginsForExtension() method to return a list of plugins. Note, that those methods will load plugins if they are not yet loaded
Once IPlugin pointer is returned by one of two methods above, it can be asked for an extension using Plugin::extension<>() method ( like plugin->extension<IMyInterface>() )

[edit] To set a dependency between plugins

Set the list of required interfaces in plugin's .desktop file

       X-KDevelop-IRequired=IMyInterface,IMyOtherInterface

It is not possible to set direct inter-plugin dependencies. The plugin shall never expect another plugin, it shall only expect an interface.

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This page has been accessed 5,257 times. This page was last modified 07:42, 10 July 2007. Content is available under GNU Free Documentation License 1.2.

Extension Interfaces and Plugins

Contents

[edit] To declare extension interface

[edit] To implement extension interface

[edit] To load a plugin that supports extension interface

[edit] To set a dependency between plugins