bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/extensions/NavigatorContentDescriptor.java - platform/eclipse.platform.ui - Git at Google

 /*******************************************************************************
  * Copyright (c) 2003, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.ui.internal.navigator.extensions;

 import java.util.Iterator;
 import java.util.Set;
 import java.util.TreeSet;

 import org.eclipse.core.expressions.ElementHandler;
 import org.eclipse.core.expressions.EvaluationContext;
 import org.eclipse.core.expressions.EvaluationResult;
 import org.eclipse.core.expressions.Expression;
 import org.eclipse.core.expressions.ExpressionConverter;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IConfigurationElement;
 import org.eclipse.core.runtime.IStatus;
 import org.eclipse.jface.viewers.ILabelProvider;
 import org.eclipse.jface.viewers.IStructuredSelection;
 import org.eclipse.jface.viewers.ITreeContentProvider;
 import org.eclipse.osgi.util.NLS;
 import org.eclipse.ui.IPluginContribution;
 import org.eclipse.ui.WorkbenchException;
 import org.eclipse.ui.internal.navigator.CommonNavigatorMessages;
 import org.eclipse.ui.internal.navigator.CustomAndExpression;
 import org.eclipse.ui.internal.navigator.NavigatorPlugin;
 import org.eclipse.ui.navigator.ICommonContentProvider;
 import org.eclipse.ui.navigator.ICommonLabelProvider;
 import org.eclipse.ui.navigator.INavigatorContentDescriptor;
 import org.eclipse.ui.navigator.Priority;

 /**
  * Encapsulates the <code>org.eclipse.ui.navigator.navigatorContent</code>
  * extension point.
  * <p>
  * <strong>EXPERIMENTAL</strong>. This class or interface has been added as
  * part of a work in progress. There is a guarantee neither that this API will
  * work nor that it will remain the same. Please do not use this API without
  * consulting with the Platform/UI team.
  * </p>
  *
  * @since 3.2
  */
 public final class NavigatorContentDescriptor implements
 		INavigatorContentDescriptor, INavigatorContentExtPtConstants {

 	private static final int HASH_CODE_NOT_COMPUTED = -1;
 	private String id;

 	private String name;

 	private IConfigurationElement configElement;

 	private int priority = Priority.NORMAL_PRIORITY_VALUE;

 	private Expression enablement;

 	private Expression possibleChildren;

 	private String icon;

 	private boolean activeByDefault;

 	private IPluginContribution contribution;

 	private Set overridingExtensions;

 	private OverridePolicy overridePolicy;

 	private String suppressedExtensionId;

 	private INavigatorContentDescriptor overriddenDescriptor;

 	private int hashCode = HASH_CODE_NOT_COMPUTED;

 	private boolean providesSaveables;

 	/**
 	 * Creates a new content descriptor from a configuration element.
 	 *
 	 * @param configElement
 	 *            configuration element to create a descriptor from
 	 *
 	 * @throws WorkbenchException
 	 *             if the configuration element could not be parsed. Reasons
 	 *             include:
 	 *             <ul>
 	 *             <li>A required attribute is missing.</li>
 	 *             <li>More elements are define than is allowed.</li>
 	 *             </ul>
 	 */
 	/* package */ NavigatorContentDescriptor(IConfigurationElement configElement)
 			throws WorkbenchException {
 		super();
 		this.configElement = configElement;
 		init();
 	}

 	/*
 	 * (non-Javadoc)
 	 *
 	 * @see org.eclipse.ui.internal.navigator.extensions.INavigatorContentDescriptor#getId()
 	 */
 	public String getId() {
 		return id;
 	}

 	/*
 	 * (non-Javadoc)
 	 *
 	 * @see org.eclipse.ui.internal.navigator.extensions.INavigatorContentDescriptor#getName()
 	 */
 	public String getName() {
 		return name;
 	}

 	/*
 	 * (non-Javadoc)
 	 *
 	 * @see org.eclipse.ui.internal.navigator.extensions.INavigatorContentDescriptor#getPriority()
 	 */
 	public int getPriority() {
 		return priority;
 	}

 	/**
 	 * Parses the configuration element.
 	 *
 	 * @throws WorkbenchException
 	 *             if the configuration element could not be parsed. Reasons
 	 *             include:
 	 *             <ul>
 	 *             <li>A required attribute is missing.</li>
 	 *             <li>More elements are define than is allowed.</li>
 	 *             </ul>
 	 */
 	private void init() throws WorkbenchException {
 		id = configElement.getAttribute(ATT_ID);
 		name = configElement.getAttribute(ATT_NAME);
 		String priorityString = configElement.getAttribute(ATT_PRIORITY);
 		icon = configElement.getAttribute(ATT_ICON);

 		String activeByDefaultString = configElement
 				.getAttribute(ATT_ACTIVE_BY_DEFAULT);
 		activeByDefault = (activeByDefaultString != null && activeByDefaultString
 				.length() > 0) ? Boolean.valueOf(
 				configElement.getAttribute(ATT_ACTIVE_BY_DEFAULT))
 				.booleanValue() : true;

 		String providesSaveablesString = configElement
 			.getAttribute(ATT_PROVIDES_SAVEABLES);
 		providesSaveables = (providesSaveablesString != null && providesSaveablesString
 				.length() > 0) ? Boolean.valueOf(providesSaveablesString)
 						.booleanValue() : false;

 		if (priorityString != null) {
 			try {
 				Priority p = Priority.get(priorityString);
 				priority = p != null ? p.getValue()
 						: Priority.NORMAL_PRIORITY_VALUE;
 			} catch (NumberFormatException exception) {
 				priority = Priority.NORMAL_PRIORITY_VALUE;
 			}
 		}
 		if (id == null) {
 			throw new WorkbenchException(NLS.bind(
 					CommonNavigatorMessages.Attribute_Missing_Warning,
 					new Object[] {
 							ATT_ID,
 							id,
 							configElement.getDeclaringExtension()
 									.getNamespaceIdentifier() }));
 		}

 		IConfigurationElement[] children = configElement
 				.getChildren(TAG_ENABLEMENT);
 		if (children.length == 0) {

 			children = configElement.getChildren(TAG_TRIGGER_POINTS);
 			if (children.length == 1) {
 				enablement = new CustomAndExpression(children[0]);
 			} else {
 				throw new WorkbenchException(NLS.bind(
 						CommonNavigatorMessages.Attribute_Missing_Warning,
 						new Object[] {
 								TAG_TRIGGER_POINTS,
 								id,
 								configElement.getDeclaringExtension()
 										.getNamespaceIdentifier() }));
 			}

 			children = configElement.getChildren(TAG_POSSIBLE_CHILDREN);
 			if (children.length == 1) {
 				possibleChildren = new CustomAndExpression(children[0]);
 			} else if(children.length > 1){
 				throw new WorkbenchException(NLS.bind(
 						CommonNavigatorMessages.Attribute_Missing_Warning,
 						new Object[] {
 								TAG_POSSIBLE_CHILDREN,
 								id,
 								configElement.getDeclaringExtension()
 										.getNamespaceIdentifier() }));
 			}
 		} else if (children.length == 1) {
 			try {
 				enablement = ElementHandler.getDefault().create(
 						ExpressionConverter.getDefault(), children[0]);
 			} catch (CoreException e) {
 				NavigatorPlugin.log(IStatus.ERROR, 0, e.getMessage(), e);
 			}
 		} else if (children.length > 1) {
 			throw new WorkbenchException(NLS.bind(
 					CommonNavigatorMessages.Attribute_Missing_Warning,
 					new Object[] {
 							TAG_ENABLEMENT,
 							id,
 							configElement.getDeclaringExtension()
 									.getNamespaceIdentifier() }));
 		}

 		contribution = new IPluginContribution() {

 			public String getLocalId() {
 				return getId();
 			}

 			public String getPluginId() {
 				return configElement.getDeclaringExtension().getNamespaceIdentifier();
 			}

 		};

 		children = configElement.getChildren(TAG_OVERRIDE);
 		if (children.length == 1) {
 			suppressedExtensionId = children[0]
 					.getAttribute(ATT_SUPPRESSED_EXT_ID);
 			overridePolicy = OverridePolicy.get(children[0]
 					.getAttribute(ATT_POLICY));
 		}
 	}

 	/**
 	 * @return Returns the icon.
 	 */
 	public String getIcon() {
 		return icon;
 	}

 	/**
 	 * @return Returns the suppressedExtensionId or null if none specified.
 	 */
 	public String getSuppressedExtensionId() {
 		return suppressedExtensionId;
 	}

 	/**
 	 * @return Returns the overridePolicy or null if this extension does not
 	 *         override another extension.
 	 */
 	public OverridePolicy getOverridePolicy() {
 		return overridePolicy;
 	}

 	/**
 	 * @return Returns the contribution.
 	 */
 	public IPluginContribution getContribution() {
 		return contribution;
 	}

 	/**
 	 * The content provider could be an instance of
 	 * {@link ICommonContentProvider}, but only {@link ITreeContentProvider} is
 	 * required.
 	 *
 	 *
 	 * @return An instance of the Content provider defined for this extension.
 	 * @throws CoreException
 	 *             if an instance of the executable extension could not be
 	 *             created for any reason
 	 *
 	 */
 	public ITreeContentProvider createContentProvider() throws CoreException {
 		return (ITreeContentProvider) configElement
 				.createExecutableExtension(ATT_CONTENT_PROVIDER);
 	}

 	/**
 	 *
 	 * The content provider could be an instance of {@link ICommonLabelProvider},
 	 * but only {@link ILabelProvider} is required.
 	 *
 	 * @return An instance of the Label provider defined for this extension
 	 * @throws CoreException
 	 *             if an instance of the executable extension could not be
 	 *             created for any reason
 	 */
 	public ILabelProvider createLabelProvider() throws CoreException {
 		return (ILabelProvider) configElement
 				.createExecutableExtension(ATT_LABEL_PROVIDER);
 	}

 	/*
 	 * (non-Javadoc)
 	 *
 	 * @see org.eclipse.ui.internal.navigator.extensions.INavigatorContentDescriptor#isEnabledByDefault()
 	 */
 	public boolean isActiveByDefault() {
 		return activeByDefault;
 	}

 	/**
 	 * Determine if this content extension would be able to provide children for
 	 * the given element.
 	 *
 	 * @param anElement
 	 *            The element that should be used for the evaluation.
 	 * @return True if and only if the extension is enabled for the element.
 	 */
 	public boolean isTriggerPoint(Object anElement) {

 		if (enablement == null || anElement == null) {
 			return false;
 		}

 		try {
 			EvaluationContext context = new EvaluationContext(null, anElement);
 			context.setAllowPluginActivation(true);
 			return (enablement.evaluate(context) == EvaluationResult.TRUE);
 		} catch (CoreException e) {
 			NavigatorPlugin.logError(0, e.getMessage(), e);
 		}
 		return false;
 	}

 	/**
 	 * Determine if this content extension could provide the given element as a
 	 * child.
 	 *
 	 * <p>
 	 * This method is used to determine what the parent of an element could be
 	 * for Link with Editor support.
 	 * </p>
 	 *
 	 * @param anElement
 	 *            The element that should be used for the evaluation.
 	 * @return True if and only if the extension might provide an object of this
 	 *         type as a child.
 	 */
 	public boolean isPossibleChild(Object anElement) {

 		if ((enablement == null && possibleChildren == null)
 				|| anElement == null) {
 			return false;
 		} else if(anElement instanceof IStructuredSelection) {
 			return arePossibleChildren((IStructuredSelection) anElement);
 		}

 		try {
 			EvaluationContext context = new EvaluationContext(null, anElement);
 			context.setAllowPluginActivation(true);
 			if (possibleChildren != null) {
 				return (possibleChildren.evaluate(context) == EvaluationResult.TRUE);
 			} else if (enablement != null) {
 				return (enablement.evaluate(context) == EvaluationResult.TRUE);
 			}
 		} catch (CoreException e) {
 			NavigatorPlugin.logError(0, e.getMessage(), e);
 		}
 		return false;
 	}

 	/**
 	 * A convenience method to check all elements in a selection.
 	 *
 	 * @param aSelection A non-null selection
 	 * @return True if and only if every element in the selection is a possible child.
 	 */
 	public boolean arePossibleChildren(IStructuredSelection aSelection) {
 		if(aSelection.isEmpty()) {
 			return false;
 		}
 		for (Iterator iter = aSelection.iterator(); iter.hasNext();) {
 			Object element = iter.next();
 			if(!isPossibleChild(element)) {
 				return false;
 			}
 		}
 		return true;
 	}

 	/**
 	 *
 	 * Does not force the creation of the set of overriding extensions.
 	 *
 	 * @return True if this extension has overridding extensions.
 	 */
 	public boolean hasOverridingExtensions() {
 		return overridingExtensions != null && overridingExtensions.size() > 0;
 	}

 	/**
 	 * @return The set of overridding extensions (of type
 	 *         {@link INavigatorContentDescriptor}
 	 */
 	public Set getOverriddingExtensions() {
 		if (overridingExtensions == null) {
 			overridingExtensions = new TreeSet(ExtensionPriorityComparator.DESCENDING);
 		}
 		return overridingExtensions;
 	}

 	/*
 	 * (non-Javadoc)
 	 *
 	 * @see java.lang.Object#toString()
 	 */
 	public String toString() {
 		return "Content[" + id + ", \"" + name + "\"]"; //$NON-NLS-1$ //$NON-NLS-2$//$NON-NLS-3$
 	}

 	/* (non-Javadoc)
 	 * @see java.lang.Object#hashCode()
 	 */
 	public int hashCode() {
 		if (hashCode == HASH_CODE_NOT_COMPUTED) {
 			String hashCodeString = configElement.getNamespaceIdentifier() + getId();
 			hashCode = hashCodeString.hashCode();
 			if (hashCode == HASH_CODE_NOT_COMPUTED)
 				hashCode++;
 		}
 		return hashCode;
 	}

 	/**
 	 * @return The descriptor of the <code>suppressedExtensionId</code> if
 	 *         non-null.
 	 */
 	public INavigatorContentDescriptor getOverriddenDescriptor() {
 		return overriddenDescriptor;
 	}

 	/**
 	 * @param theOverriddenDescriptor
 	 *            The overriddenDescriptor to set.
 	 */
 	/* package */void setOverriddenDescriptor(
 			INavigatorContentDescriptor theOverriddenDescriptor) {
 		overriddenDescriptor = theOverriddenDescriptor;
 	}

 	/* (non-Javadoc)
 	 * @see org.eclipse.ui.navigator.INavigatorContentDescriptor#hasSaveablesProvider()
 	 */
 	public boolean hasSaveablesProvider() {
 		return providesSaveables;
 	}

 }
	/*******************************************************************************
	* Copyright (c) 2003, 2006 IBM Corporation and others.
	* All rights reserved. This program and the accompanying materials
	* are made available under the terms of the Eclipse Public License v1.0
	* which accompanies this distribution, and is available at
	* http://www.eclipse.org/legal/epl-v10.html
	*
	* Contributors:
	* IBM Corporation - initial API and implementation
	*******************************************************************************/
	package org.eclipse.ui.internal.navigator.extensions;

	import java.util.Iterator;
	import java.util.Set;
	import java.util.TreeSet;

	import org.eclipse.core.expressions.ElementHandler;
	import org.eclipse.core.expressions.EvaluationContext;
	import org.eclipse.core.expressions.EvaluationResult;
	import org.eclipse.core.expressions.Expression;
	import org.eclipse.core.expressions.ExpressionConverter;
	import org.eclipse.core.runtime.CoreException;
	import org.eclipse.core.runtime.IConfigurationElement;
	import org.eclipse.core.runtime.IStatus;
	import org.eclipse.jface.viewers.ILabelProvider;
	import org.eclipse.jface.viewers.IStructuredSelection;
	import org.eclipse.jface.viewers.ITreeContentProvider;
	import org.eclipse.osgi.util.NLS;
	import org.eclipse.ui.IPluginContribution;
	import org.eclipse.ui.WorkbenchException;
	import org.eclipse.ui.internal.navigator.CommonNavigatorMessages;
	import org.eclipse.ui.internal.navigator.CustomAndExpression;
	import org.eclipse.ui.internal.navigator.NavigatorPlugin;
	import org.eclipse.ui.navigator.ICommonContentProvider;
	import org.eclipse.ui.navigator.ICommonLabelProvider;
	import org.eclipse.ui.navigator.INavigatorContentDescriptor;
	import org.eclipse.ui.navigator.Priority;

	/**
	* Encapsulates the <code>org.eclipse.ui.navigator.navigatorContent</code>
	* extension point.
	* <p>
	* <strong>EXPERIMENTAL</strong>. This class or interface has been added as
	* part of a work in progress. There is a guarantee neither that this API will
	* work nor that it will remain the same. Please do not use this API without
	* consulting with the Platform/UI team.
	* </p>
	*
	* @since 3.2
	*/
	public final class NavigatorContentDescriptor implements
	INavigatorContentDescriptor, INavigatorContentExtPtConstants {

	private static final int HASH_CODE_NOT_COMPUTED = -1;
	private String id;

	private String name;

	private IConfigurationElement configElement;

	private int priority = Priority.NORMAL_PRIORITY_VALUE;

	private Expression enablement;

	private Expression possibleChildren;

	private String icon;

	private boolean activeByDefault;

	private IPluginContribution contribution;

	private Set overridingExtensions;

	private OverridePolicy overridePolicy;

	private String suppressedExtensionId;

	private INavigatorContentDescriptor overriddenDescriptor;

	private int hashCode = HASH_CODE_NOT_COMPUTED;

	private boolean providesSaveables;

	/**
	* Creates a new content descriptor from a configuration element.
	*
	* @param configElement
	* configuration element to create a descriptor from
	*
	* @throws WorkbenchException
	* if the configuration element could not be parsed. Reasons
	* include:
	* <ul>
	* <li>A required attribute is missing.</li>
	* <li>More elements are define than is allowed.</li>
	* </ul>
	*/
	/* package */ NavigatorContentDescriptor(IConfigurationElement configElement)
	throws WorkbenchException {
	super();
	this.configElement = configElement;
	init();
	}

	/*
	* (non-Javadoc)
	*
	* @see org.eclipse.ui.internal.navigator.extensions.INavigatorContentDescriptor#getId()
	*/
	public String getId() {
	return id;
	}

	/*
	* (non-Javadoc)
	*
	* @see org.eclipse.ui.internal.navigator.extensions.INavigatorContentDescriptor#getName()
	*/
	public String getName() {
	return name;
	}

	/*
	* (non-Javadoc)
	*
	* @see org.eclipse.ui.internal.navigator.extensions.INavigatorContentDescriptor#getPriority()
	*/
	public int getPriority() {
	return priority;
	}

	/**
	* Parses the configuration element.
	*
	* @throws WorkbenchException
	* if the configuration element could not be parsed. Reasons
	* include:
	* <ul>
	* <li>A required attribute is missing.</li>
	* <li>More elements are define than is allowed.</li>
	* </ul>
	*/
	private void init() throws WorkbenchException {
	id = configElement.getAttribute(ATT_ID);
	name = configElement.getAttribute(ATT_NAME);
	String priorityString = configElement.getAttribute(ATT_PRIORITY);
	icon = configElement.getAttribute(ATT_ICON);

	String activeByDefaultString = configElement
	.getAttribute(ATT_ACTIVE_BY_DEFAULT);
	activeByDefault = (activeByDefaultString != null && activeByDefaultString
	.length() > 0) ? Boolean.valueOf(
	configElement.getAttribute(ATT_ACTIVE_BY_DEFAULT))
	.booleanValue() : true;

	String providesSaveablesString = configElement
	.getAttribute(ATT_PROVIDES_SAVEABLES);
	providesSaveables = (providesSaveablesString != null && providesSaveablesString
	.length() > 0) ? Boolean.valueOf(providesSaveablesString)
	.booleanValue() : false;

	if (priorityString != null) {
	try {
	Priority p = Priority.get(priorityString);
	priority = p != null ? p.getValue()
	: Priority.NORMAL_PRIORITY_VALUE;
	} catch (NumberFormatException exception) {
	priority = Priority.NORMAL_PRIORITY_VALUE;
	}
	}
	if (id == null) {
	throw new WorkbenchException(NLS.bind(
	CommonNavigatorMessages.Attribute_Missing_Warning,
	new Object[] {
	ATT_ID,
	id,
	configElement.getDeclaringExtension()
	.getNamespaceIdentifier() }));
	}

	IConfigurationElement[] children = configElement
	.getChildren(TAG_ENABLEMENT);
	if (children.length == 0) {

	children = configElement.getChildren(TAG_TRIGGER_POINTS);
	if (children.length == 1) {
	enablement = new CustomAndExpression(children[0]);
	} else {
	throw new WorkbenchException(NLS.bind(
	CommonNavigatorMessages.Attribute_Missing_Warning,
	new Object[] {
	TAG_TRIGGER_POINTS,
	id,
	configElement.getDeclaringExtension()
	.getNamespaceIdentifier() }));
	}

	children = configElement.getChildren(TAG_POSSIBLE_CHILDREN);
	if (children.length == 1) {
	possibleChildren = new CustomAndExpression(children[0]);
	} else if(children.length > 1){
	throw new WorkbenchException(NLS.bind(
	CommonNavigatorMessages.Attribute_Missing_Warning,
	new Object[] {
	TAG_POSSIBLE_CHILDREN,
	id,
	configElement.getDeclaringExtension()
	.getNamespaceIdentifier() }));
	}
	} else if (children.length == 1) {
	try {
	enablement = ElementHandler.getDefault().create(
	ExpressionConverter.getDefault(), children[0]);
	} catch (CoreException e) {
	NavigatorPlugin.log(IStatus.ERROR, 0, e.getMessage(), e);
	}
	} else if (children.length > 1) {
	throw new WorkbenchException(NLS.bind(
	CommonNavigatorMessages.Attribute_Missing_Warning,
	new Object[] {
	TAG_ENABLEMENT,
	id,
	configElement.getDeclaringExtension()
	.getNamespaceIdentifier() }));
	}

	contribution = new IPluginContribution() {

	public String getLocalId() {
	return getId();
	}

	public String getPluginId() {
	return configElement.getDeclaringExtension().getNamespaceIdentifier();
	}

	};

	children = configElement.getChildren(TAG_OVERRIDE);
	if (children.length == 1) {
	suppressedExtensionId = children[0]
	.getAttribute(ATT_SUPPRESSED_EXT_ID);
	overridePolicy = OverridePolicy.get(children[0]
	.getAttribute(ATT_POLICY));
	}
	}

	/**
	* @return Returns the icon.
	*/
	public String getIcon() {
	return icon;
	}

	/**
	* @return Returns the suppressedExtensionId or null if none specified.
	*/
	public String getSuppressedExtensionId() {
	return suppressedExtensionId;
	}

	/**
	* @return Returns the overridePolicy or null if this extension does not
	* override another extension.
	*/
	public OverridePolicy getOverridePolicy() {
	return overridePolicy;
	}

	/**
	* @return Returns the contribution.
	*/
	public IPluginContribution getContribution() {
	return contribution;
	}

	/**
	* The content provider could be an instance of
	* {@link ICommonContentProvider}, but only {@link ITreeContentProvider} is
	* required.
	*
	*
	* @return An instance of the Content provider defined for this extension.
	* @throws CoreException
	* if an instance of the executable extension could not be
	* created for any reason
	*
	*/
	public ITreeContentProvider createContentProvider() throws CoreException {
	return (ITreeContentProvider) configElement
	.createExecutableExtension(ATT_CONTENT_PROVIDER);
	}

	/**
	*
	* The content provider could be an instance of {@link ICommonLabelProvider},
	* but only {@link ILabelProvider} is required.
	*
	* @return An instance of the Label provider defined for this extension
	* @throws CoreException
	* if an instance of the executable extension could not be
	* created for any reason
	*/
	public ILabelProvider createLabelProvider() throws CoreException {
	return (ILabelProvider) configElement
	.createExecutableExtension(ATT_LABEL_PROVIDER);
	}

	/*
	* (non-Javadoc)
	*
	* @see org.eclipse.ui.internal.navigator.extensions.INavigatorContentDescriptor#isEnabledByDefault()
	*/
	public boolean isActiveByDefault() {
	return activeByDefault;
	}

	/**
	* Determine if this content extension would be able to provide children for
	* the given element.
	*
	* @param anElement
	* The element that should be used for the evaluation.
	* @return True if and only if the extension is enabled for the element.
	*/
	public boolean isTriggerPoint(Object anElement) {

	if (enablement == null \|\| anElement == null) {
	return false;
	}

	try {
	EvaluationContext context = new EvaluationContext(null, anElement);
	context.setAllowPluginActivation(true);
	return (enablement.evaluate(context) == EvaluationResult.TRUE);
	} catch (CoreException e) {
	NavigatorPlugin.logError(0, e.getMessage(), e);
	}
	return false;
	}

	/**
	* Determine if this content extension could provide the given element as a
	* child.
	*
	* <p>
	* This method is used to determine what the parent of an element could be
	* for Link with Editor support.
	* </p>
	*
	* @param anElement
	* The element that should be used for the evaluation.
	* @return True if and only if the extension might provide an object of this
	* type as a child.
	*/
	public boolean isPossibleChild(Object anElement) {

	if ((enablement == null && possibleChildren == null)
	\|\| anElement == null) {
	return false;
	} else if(anElement instanceof IStructuredSelection) {
	return arePossibleChildren((IStructuredSelection) anElement);
	}

	try {
	EvaluationContext context = new EvaluationContext(null, anElement);
	context.setAllowPluginActivation(true);
	if (possibleChildren != null) {
	return (possibleChildren.evaluate(context) == EvaluationResult.TRUE);
	} else if (enablement != null) {
	return (enablement.evaluate(context) == EvaluationResult.TRUE);
	}
	} catch (CoreException e) {
	NavigatorPlugin.logError(0, e.getMessage(), e);
	}
	return false;
	}

	/**
	* A convenience method to check all elements in a selection.
	*
	* @param aSelection A non-null selection
	* @return True if and only if every element in the selection is a possible child.
	*/
	public boolean arePossibleChildren(IStructuredSelection aSelection) {
	if(aSelection.isEmpty()) {
	return false;
	}
	for (Iterator iter = aSelection.iterator(); iter.hasNext();) {
	Object element = iter.next();
	if(!isPossibleChild(element)) {
	return false;
	}
	}
	return true;
	}

	/**
	*
	* Does not force the creation of the set of overriding extensions.
	*
	* @return True if this extension has overridding extensions.
	*/
	public boolean hasOverridingExtensions() {
	return overridingExtensions != null && overridingExtensions.size() > 0;
	}

	/**
	* @return The set of overridding extensions (of type
	* {@link INavigatorContentDescriptor}
	*/
	public Set getOverriddingExtensions() {
	if (overridingExtensions == null) {
	overridingExtensions = new TreeSet(ExtensionPriorityComparator.DESCENDING);
	}
	return overridingExtensions;
	}

	/*
	* (non-Javadoc)
	*
	* @see java.lang.Object#toString()
	*/
	public String toString() {
	return "Content[" + id + ", \"" + name + "\"]"; //$NON-NLS-1$ //$NON-NLS-2$//$NON-NLS-3$
	}

	/* (non-Javadoc)
	* @see java.lang.Object#hashCode()
	*/
	public int hashCode() {
	if (hashCode == HASH_CODE_NOT_COMPUTED) {
	String hashCodeString = configElement.getNamespaceIdentifier() + getId();
	hashCode = hashCodeString.hashCode();
	if (hashCode == HASH_CODE_NOT_COMPUTED)
	hashCode++;
	}
	return hashCode;
	}

	/**
	* @return The descriptor of the <code>suppressedExtensionId</code> if
	* non-null.
	*/
	public INavigatorContentDescriptor getOverriddenDescriptor() {
	return overriddenDescriptor;
	}

	/**
	* @param theOverriddenDescriptor
	* The overriddenDescriptor to set.
	*/
	/* package */void setOverriddenDescriptor(
	INavigatorContentDescriptor theOverriddenDescriptor) {
	overriddenDescriptor = theOverriddenDescriptor;
	}

	/* (non-Javadoc)
	* @see org.eclipse.ui.navigator.INavigatorContentDescriptor#hasSaveablesProvider()
	*/
	public boolean hasSaveablesProvider() {
	return providesSaveables;
	}

	}