Eclipse Property Testers (Test expression) 的使用-优快云博客

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;
	}
}