Eclipse Plug-in Developer Guide (Galileo) - Context (Eclipse Platform API Specification)

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Eclipse Platform
Release 3.5

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org.eclipse.core.commands.contexts
Class Context


java.lang.Object
  

org.eclipse.core.commands.common.EventManager
      

org.eclipse.core.commands.common.HandleObject
          

org.eclipse.core.commands.common.NamedHandleObject
              
org.eclipse.core.commands.contexts.Context

All Implemented Interfaces:: Comparable, IIdentifiable

public final class Context
extends NamedHandleObject
implements Comparable
extends NamedHandleObject
implements Comparable

A context is an answer to the question "when". Other services can listen for the activation and deactivation of contexts, and change their own state in response to these changes. For example, Eclipse's key binding service listens to context activation and deactivation to determine which key bindings should be active.

An instance of this interface can be obtained from an instance of ContextManager for any identifier, whether or not an context with that identifier is defined in the extension registry.

The handle-based nature of this API allows it to work well with runtime plugin activation and deactivation. If a context is defined, that means that its corresponding plug-in is active. If the plug-in is then deactivated, the context will still exist but it will be undefined. An attempts to use an undefined context will result in a NotDefinedException being thrown.

This class is not intended to be extended by clients.

Since:: 3.1
See Also:: ContextManager

Field Summary

Fields inherited from class org.eclipse.core.commands.common. NamedHandleObject

description, name

Fields inherited from class org.eclipse.core.commands.common. HandleObject

defined, id, string

Method Summary

void addContextListener ( IContextListener listener)
          Registers an instance of IContextListener to listen for changes to properties of this instance.

int compareTo ( Object object)


void define ( String name, String description, String parentId)
           Defines this context by giving it a name, and possibly a description and a parent identifier as well.

String getParentId ()
          Returns the identifier of the parent of this instance.

void removeContextListener ( IContextListener contextListener)
          Unregisters an instance of IContextListener listening for changes to properties of this instance.

String toString ()
          The string representation of this context -- for debugging purposes only.

void undefine ()
          Makes this context become undefined.

Methods inherited from class org.eclipse.core.commands.common. NamedHandleObject

getDescription, getName

Methods inherited from class org.eclipse.core.commands.common. HandleObject

equals, getId, hashCode, isDefined

Methods inherited from class org.eclipse.core.commands.common. EventManager

addListenerObject, clearListeners, getListeners, isListenerAttached, removeListenerObject

Methods inherited from class java.lang. Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Method Detail

addContextListener

public final void addContextListener(
IContextListener listener)

Registers an instance of IContextListener to listen for changes to properties of this instance.

Parameters:: listener - the instance to register. Must not be null. If an attempt is made to register an instance which is already registered with this instance, no operation is performed.

compareTo

public final int compareTo(
Object object)

Specified by:: compareTo in interface Comparable

define

public final void define(
String name,
                         
String description,
                         
String parentId)

Defines this context by giving it a name, and possibly a description and a parent identifier as well. The defined property automatically becomes true.

Notification is sent to all listeners that something has changed.

Parameters:: name - The name of this context; must not be null.; description - The description for this context; may be null.; parentId - The parent identifier for this context; may be null.

getParentId

public final 
String getParentId()
                         throws 
NotDefinedException

Returns the identifier of the parent of this instance.

Notification is sent to all registered listeners if this property changes.

Returns:: the identifier of the parent of this instance. May be null.
Throws:: NotDefinedException - if this instance is not defined.

removeContextListener

public final void removeContextListener(
IContextListener contextListener)

Unregisters an instance of IContextListener listening for changes to properties of this instance.

Parameters:: contextListener - the instance to unregister. Must not be null. If an attempt is made to unregister an instance which is not already registered with this instance, no operation is performed.

toString

public final 
String toString()

The string representation of this context -- for debugging purposes only. This string should not be shown to an end user.

Specified by:: toString in class HandleObject

Returns:: The string representation; never null.

undefine

public final void undefine()

Makes this context become undefined. This has the side effect of changing the name, description and parent identifier to null. Notification is sent to all listeners.

Specified by:: undefine in class HandleObject