Eclipse Property Testers (Test expression) 的使用

Eclipse Resource Plugin里面很多值得一看的东西，其中一个就是Property Testers ，它在某些条件过滤的时候非常有用，先看一段jdt里面的使用

      <page            objectClass="org.eclipse.core.resources.IProject"            name="%javaCategoryPageName"            class="org.eclipse.jdt.internal.ui.preferences.JavaCategoryPropertyPage"            id="org.eclipse.jdt.ui.propertyPages.JavaCategoryPropertyPage">         <enabledWhen>		     <adapt type="org.eclipse.core.resources.IProject">		          <test property="org.eclipse.core.resources.projectNature" value="org.eclipse.jdt.core.javanature"/>		     </adapt>                  </enabledWhen>      </page>

?这里的

org.eclipse.core.resources.projectNature

就是eclipse已经定义好的property。

简介

扩展点：org.eclipse.core.expressions.propertyTesters

作用：用来给一个已知的类型添加属性测试支持，新添加的属性可以用于各种表达式条件判断。

扩展语法：

<!ELEMENT propertyTester EMPTY><!ATTLIST propertyTester    id    CDATA #REQUIRED    type   CDATA #REQUIRED   namespace  CDATA #REQUIRED   properties CDATA #REQUIRED   class  CDATA #REQUIRED>

? 引用一下Eclipse自己的解释：

id - unique identifier for the property tester
type - the type to be extended by this property tester
namespace - a unique id determining the name space the properties are added to
properties - a comma separated list of properties provided by this property tester
class - the name of the class that implements the testing methods. The class must be public and extend org.eclipse.core.expressions.PropertyTester with a public 0-argument constructor.

示例

     <extension           point="org.eclipse.core.expressions.propertyTesters">        <propertyTester              id="org.eclipse.core.expressions.bundlePropertyTester"              type="org.eclipse.core.runtime.Platform"              namespace="org.eclipse.core.runtime"              properties="product,isBundleInstalled,bundleState"              class="org.eclipse.core.internal.expressions.propertytester.PlatformPropertyTester">        </propertyTester>     </extension>

很简单的一个使用，这些都在eclipse的文档里面说的很清楚了。

至于org.eclipse.core.expressions.PropertyTester如何扩展，也很简单，一般只需要实现test(Object receiver, String property, Object[] args,? Object expectedValue)方法就行了。比如：

/******************************************************************************* * Copyright (c) 2006, 2008 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.core.internal.expressions.propertytester;import org.osgi.framework.Bundle;import org.eclipse.core.expressions.PropertyTester;import org.eclipse.core.runtime.IProduct;import org.eclipse.core.runtime.Platform;/** * A property tester for testing platform properties. Can test whether or * not a given bundle is installed in the running environment, as well as * the id of the currently active product. * <p> * For example:<br /> * &lt;test property="org.eclipse.core.runtime.product" value="org.eclipse.sdk.ide"/&gt; <br /> * &lt;test property="org.eclipse.core.runtime.isBundleInstalled" args="org.eclipse.core.expressions"/&gt; <br /> * &lt;test property="org.eclipse.core.runtime.bundleState" args="org.eclipse.core.expressions" value="ACTIVE"/&gt; * <p> */public class PlatformPropertyTester extends PropertyTester {	private static final String PROPERTY_PRODUCT = "product"; //$NON-NLS-1$	private static final String PROPERTY_IS_BUNDLE_INSTALLED = "isBundleInstalled"; //$NON-NLS-1$	private static final String PROPERTY_BUNDLE_STATE = "bundleState"; //$NON-NLS-1$	/* (non-Javadoc)	 * @see org.eclipse.core.expressions.IPropertyTester#test(java.lang.Object, java.lang.String, java.lang.Object[], java.lang.Object)	 */	public boolean test(Object receiver, String property, Object[] args, Object expectedValue) {		if (Platform.class.equals(receiver)) {			if (PROPERTY_PRODUCT.equals(property)) {				IProduct product= Platform.getProduct();				if (product != null) {					return product.getId().equals(expectedValue);				}				return false;			} else if (PROPERTY_IS_BUNDLE_INSTALLED.equals(property) && args.length >= 1 && args[0] instanceof String) {				return Platform.getBundle((String)args[0]) != null;			} else if (PROPERTY_BUNDLE_STATE.equals(property)					&& args.length >= 1 && args[0] instanceof String) {				Bundle b = Platform.getBundle((String) args[0]);				if (b != null) {					return bundleState(b.getState(), expectedValue);				}				return false;			}		}		return false;	}	private boolean bundleState(int bundleState, Object expectedValue) {		if ("UNINSTALLED".equals(expectedValue)) { //$NON-NLS-1$			return bundleState == Bundle.UNINSTALLED;		}		if ("INSTALLED".equals(expectedValue)) { //$NON-NLS-1$			return bundleState == Bundle.INSTALLED;		}		if ("RESOLVED".equals(expectedValue)) { //$NON-NLS-1$			return bundleState == Bundle.RESOLVED;		}		if ("STARTING".equals(expectedValue)) { //$NON-NLS-1$			return bundleState == Bundle.STARTING;		}		if ("STOPPING".equals(expectedValue)) { //$NON-NLS-1$			return bundleState == Bundle.STOPPING;		}		if ("ACTIVE".equals(expectedValue)) { //$NON-NLS-1$			return bundleState == Bundle.ACTIVE;		}		return false;	}}