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1 /*******************************************************************************
2  * Copyright (c) 2000, 2006 IBM Corporation and others.
3  * All rights reserved. This program and the accompanying materials
4  * are made available under the terms of the Eclipse Public License v1.0
5  * which accompanies this distribution, and is available at
6  * http://www.eclipse.org/legal/epl-v10.html
7  *
8  * Contributors:
9  * IBM Corporation - initial API and implementation
10  *******************************************************************************/
11 package org.eclipse.ui;
12
13 import org.eclipse.jface.action.IAction;
14 import org.eclipse.jface.viewers.ISelection;
15
16 /**
17  * Interface for actions contributed via an extension point.
18  * <p>
19  * This interface should be implemented by clients who need to contribute actions
20  * via an extension point. The workbench will generate a <b>proxy action</b>
21  * object on behalf of the plug-in to avoid having to activate the plug-in until
22  * the user needs it. If the action is performed the workbench will load the class
23  * that implements this interface and create what is called an <b>action
24  * delegate</b> object. Then the request, and all subsequent ones, are
25  * forwarded through the proxy action to the action delegate, which does the
26  * real work.
27  * </p><p>
28  * The proxy action is the one that appears in the UI, so the action delegate
29  * will need to talk to the proxy action in order to keep up an appropriate
30  * appearance. Once the action delegate has been created, it will be
31  * notified of all selection changes, allowing it to enable or disable the
32  * proxy action appropriately.
33  * </p><p>
34  * An action delegate cannot be consulted about selection changes before the
35  * action is performed because it does not exist. For this reason, control of
36  * the action's enable state should also be exercised through simple XML rules
37  * contained in the extension. These rules allow enable state control before
38  * the action delegate's plug-in is loaded.
39  * </p><p>
40  * Clients can choose to subclass the provided abstract implementation
41  * <code>org.eclipse.ui.actions.ActionDelegate</code> or implement the
42  * interface directly.
43  * </p>
44  *
45  * @see org.eclipse.ui.actions.ActionDelegate
46  * @see org.eclipse.ui.IActionDelegate2
47  */
48 public interface IActionDelegate {
49     /**
50      * Performs this action.
51      * <p>
52      * This method is called by the proxy action when the action has been
53      * triggered. Implement this method to do the actual work.
54      * </p><p>
55      * <b>Note:</b> If the action delegate also implements
56      * <code>IActionDelegate2</code>, then this method is not invoked but
57      * instead the <code>runWithEvent(IAction, Event)</code> method is called.
58      * </p>
59      *
60      * @param action the action proxy that handles the presentation portion of the
61      * action
62      */
63     public void run(IAction action);
64
65     /**
66      * Notifies this action delegate that the selection in the workbench has changed.
67      * <p>
68      * Implementers can use this opportunity to change the availability of the
69      * action or to modify other presentation properties.
70      * </p><p>
71      * When the selection changes, the action enablement state is updated based on
72      * the criteria specified in the plugin.xml file. Then the delegate is notified
73      * of the selection change regardless of whether the enablement criteria in the
74      * plugin.xml file is met.
75      * </p>
76      *
77      * @param action the action proxy that handles presentation portion of
78      * the action
79      * @param selection the current selection, or <code>null</code> if there
80      * is no selection.
81      */
82     public void selectionChanged(IAction action, ISelection selection);
83 }
84
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