Eclipse command framework core expression: Property tester

Addition to Eclipse command framework series, this post explains use of property tester to control command’s enable/visible properties. In earlier post we have tried declarative way to achieve same thing but property tester gives us more control.

Property tester is associated with, tester class which implements PropertyTester.java, a namespace and set of property which it supports. We can refer this property tester using its namespace + a property name. It gives you call back to test() method with property name as parameter inside property tester class. We can configure property tester for type of input parameter.

Here is sample declaration of property tester extension point

<extension

        point="org.eclipse.core.expressions.propertyTesters">

     <propertyTester

           class="com.example.advance.cmd.EditorTester"

           id="com.example.advance.cmd.propertyTester1"

           namespace="com.example.advance.cmd"

           properties="isEditor1,isEditor2"

           type="org.eclipse.ui.editors.text.TextEditor">

     </propertyTester>

 </extension>

• Type : type to be extended  by property tester
  
  
• class:Property tester class which extends “org.eclipse.core.resources.PropertyTester” class and provides implementation for test() method.
  
  
• namesopace: distinguish this property tester from other.
  
  
• properties: Properties supporter by this property tester.

Note: To extend “org.eclipse.core.expression.propertytester” extension point, plug-in project needs “org.eclipse.core.expression” dependency.

Extending “org.eclipse.core.resources.propertytester” extension point.



Here is the sample PropertyTester’s implementation

package com.example.advance.cmd;

import org.eclipse.core.expressions.PropertyTester;

import com.example.advance.cmd.editor.Editor1;

import com.example.advance.cmd.editor.Editor2;

public class EditorTester extends PropertyTester{

    @Override

    public boolean test(Object receiver, String property, Object[] args,

            Object expectedValue) {

        if("isEditory1".equalsIgnoreCase(property)){

            if(receiver instanceof Editor1){

                return true;

            }

        }else if("isEditor2".equalsIgnoreCase(property)){

            if(receiver instanceof Editor2){

                return true;

            }

        }

        return false;

    }

}

Using property tester for enable command



PLugin.xml will be like below

<extension

        point="org.eclipse.ui.menus">

     <menuContribution

           allPopups="true"

           locationURI="popup:#TextEditorContext?after=additions">

        <command

              commandId="com.example.advance.cmd.command1"

              label="Command One"

              style="push"

              tooltip="Command 1">

           <visibleWhen

                 checkEnabled="true">

           </visibleWhen>

        </command>

     </menuContribution>

  </extension>

  <extension

        point="org.eclipse.ui.handlers">

     <handler

           class="com.example.advance.cmd.Cmd1Handler1"

           commandId="com.example.advance.cmd.command1">

        <enabledWhen>

           <with

                 variable="activeEditor">

              <test

                    forcePluginActivation="true"

                    property="com.example.advance.cmd.isEditor1">

              </test>

           </with>

        </enabledWhen>

     </handler>

  </extension>

Here I have enabled “Command One” only for test “com.example.advance.cmd.iEditor2” property test and visible only when it is enable. Result of this you can notice here that “Command One” is visible only in Editor1 not in Editor2 in images below.