Command Core Expressions

Core expressions are declarative or programmatic expressions based on the org.eclipse.core.expressions plugin.

Expressions and the Command Framework

The Platform Command Framework uses core expressions for enabledWhen and activeWhen for handlers, programmatic activation of contexts, and for visibleWhen for menu contributions. The command framework provides the IEvaluationContext that command core expressions are evaluate against.

The IEvaluationContext provides a default variable for evaluations, and a number of named variables. In the command framework, we provide the global selection as a java.util.Collection as the default variable. It can either be empty, have one entry (if the ISelection was something like an ITextSelection), or have the contents of an IStructuredSelection.

The <with/> element can be used to change which variable the child expression elements are evaluating against.

Variables and the Command Framework

The variables used for command framework evaluation are listed in ISources.java

Some of the variables may not be set, depending on the current application context when they are evaluated.

Name	Type	Description	Since
activeContexts	A java.util.Collection of java.lang.String	This is a collection of the active context IDs as strings. Most commonly used with <iterate/>, <count/>, and <test/> with a combined org.eclipse.common.expressions.PropertyTester. In 3.3 action sets are mirrored by contexts whose parent is org.eclipse.ui.actionSet, and the active action sets show up in the list of active contexts.	3.2
activeActionSets	An IActionSetDescriptor[]	Note: This is currently not used as it points to an internal class and the type might change in any release.	3.2
activeShell	org.eclipse.swt.widgets.Shell	The currently active shell. It can be a dialog or workbench window shell.	3.2
activeWorkbenchWindowShell	org.eclipse.swt.widgets.Shell	The active workbench window shell.	3.2
activeWorkbenchWindow	org.eclipse.ui.IWorkbenchWindow	The active workbench window.	3.2
activeWorkbenchWindow.isCoolbarVisible	java.lang.Boolean	Reports coolbar visibility for the currently active workbench window.	3.3
activeWorkbenchWindow.isPerspectiveBarVisible	java.lang.Boolean	Reports perspective bar visibility for the currently active workbench window.	3.3
activeWorkbenchWindow.activePerspective	java.lang.String	Reports the name of the current perspective of the active workbench window.	3.4
activeEditor	org.eclipse.ui.IEditorPart	The currently active editor. This is remembered even if the editor is not the currently active part.	3.2
activeEditorId	java.lang.String	The ID of the currently active editor. This can be used for expressions on the editor type.	3.2
activePart	org.eclipse.ui.IWorkbenchPart	The active part, which can be the same as the active editor.	3.2
activePartId	java.lang.String	The ID of the currently active part.	3.2
activeSite	org.eclipse.ui.IWorkbenchPartSite	The site of the currently active part.	3.2
selection	org.eclipse.jface.viewers.ISelection	The current global selection. It is often used with <test/> elements with org.eclipse.core.expressions.PropertyTester, in programmatic core expressions, and in 3.3 with <iterate/> and <count/> elements.	3.2
activeMenu	A java.util.Collection of java.lang.String	This is the list of IDs of the showing context menu. Examples are like #TextEditorRuler or a part ID. Most commonly used with <iterate/>, <count/>, and <test/> with a combined org.eclipse.common.expressions.PropertyTester.	3.2
activeMenuSelection	org.eclipse.jface.viewers.ISelection	This is a selection that is available while a context menu is showing. It is the selection from the selection provider used to register the context menu, usually from getSite().registerContextMenu(*). It is usually the same as the selectionvariable, but not always. This is more for legacy compatibility.	3.3
activeMenuEditorInput	org.eclipse.jface.viewers.ISelection	This is a selection that is available while a context menu is showing. It is the selection from the editor input, usually if includeEditorInput was set to true during getEditorSite().registerContextMenu(*). This is more for legacy compatibility.	3.3
activeFocusControl	org.eclipse.swt.widgets.Control	A control that has focus and has been registered with the IFocusService.	3.3
activeFocusControlId	java.lang.String	The ID of a control that has focus and has been registered with the org.eclipse.ui.swt.IFocusService.	3.3

Note: All these variables can be used with <test/> and a org.eclipse.common.expressions.PropertyTester.

Property Testers

The Eclipse SDK provides a couple of property testers that can be used in core expressions. The expression defines a property attribute and then takes a combination of args and a value that is tester implementation dependent. The property attribute is the combination of the namespace and property name. For example, to test an IResource name the property would be org.eclipse.core.resources.name.

Namespace	Type	Implementation
org.eclipse.core.runtime	org.eclipse.core.runtime.Platform	PlatformPropertyTester.java
Property	Description
product	Test the id of the currently active product.
isBundleInstalled	Test if a given bundle is installed in the running environment. Use the args attribute to pass in the bundle id.
Namespace	Type	Implementation
org.eclipse.core.resources	org.eclipse.core.resources.IResource	ResourcePropertyTester.java
Property	Description
name	A property indicating the file name (value "name"). "*" and "?" wild cards are supported.
path	A property indicating the file path (value "path"). "*" and "?" wild cards are supported.
extension	A property indicating the file extension (value "extension"). "*" and "?" wild cards are supported.
readOnly	A property indicating whether the file is read only (value "readOnly").
projectNature	A property indicating the project nature (value "projectNature").
persistentProperty	A property indicating a persistent property on the selected resource (value "persistentProperty"). If two arguments are given, this treats the first as the property name, and the second as the expected property value. If only one argument (or just the expected value) is given, this treats it as the property name, and simply tests for existence of the property on the resource.
projectPersistentProperty	A property indicating a persistent property on the selected resource's project. (value "projectPersistentProperty"). If two arguments are given, this treats the first as the property name, and the second as the expected property value. If only one argument (or just the expected value) is given, this treats it as the property name, and simply tests for existence of the property on the resource.
sessionProperty	A property indicating a session property on the selected resource (value "sessionProperty"). If two arguments are given, this treats the first as the property name, and the second as the expected property value. If only one argument (or just the expected value) is given, this treats it as the property name, and simply tests for existence of the property on the resource.
projectSessionProperty	A property indicating a session property on the selected resource's project. (value "projectSessionProperty"). If two arguments are given, this treats the first as the property name, and the second as the expected property value. If only one argument (or just the expected value) is given, this treats it as the property name, and simply tests for existence of the property on the resource.
Namespace	Type	Implementation
org.eclipse.core.resources	org.eclipse.core.resources.IFile	FilePropertyTester.java
Property	Description
contentTypeId	A property indicating that we are looking to verify that the file matches the content type matching the given identifier. The identifier is provided as the expected value.
Namespace	Type	Implementation
org.eclipse.core.resources	org.eclipse.core.resources.IProject	ProjectPropertyTester.java
Property	Description
open	A property indicating whether the project is open (value "open").
Namespace	Type	Implementation
org.eclipse.core.resources	org.eclipse.core.resources.mapping.ResourceMapping	ResourceMappingPropertyTester.java
Property	Description
projectPersistentProperty	A property indicating a persistent property on the selected resource's project. (value "projectPersistentProperty"). If two arguments are given, this treats the first as the property name, and the second as the expected property value. If only one argument (or just the expected value) is given, this treats it as the property name, and simply tests for existence of the property on the resource.
Namespace	Type	Implementation
org.eclipse.ui	org.eclipse.ui.IWorkbench	ActivityPropertyTester.java
Property	Description
isActivityEnabled	Test if the activity in args is enabled.
isCategoryEnabled	Test if the category in args is enabled.
Namespace	Type	Implementation
org.eclipse.ui.workbenchWindow	org.eclipse.ui.IWorkbenchWindow	OpenPerspectivePropertyTester.java
Property	Description
isPerspectiveOpen	Tests if any perspective is open.

Expression examples

Here are some examples. I'll pretend all of the examples are deciding when a handler is active.

Basic IStructuredSelection

A view provides a structured selection through its selection provider. An example would be the InfoView in org.eclipse.ui.examples.contributions. You can browse the plugin.xml and InfoView.java files. The InfoView provides an IStructuredSelection with 0 or more org.eclipse.ui.examples.contributions.model.Person.

When using the default variable, you must treat it as an java.util.Collection. That means using <count> or <iterate>

<activeWhen>
    <iterate>
       <instanceof value="org.eclipse.ui.examples.contributions.model.Person"/>
    </iterate>
</activeWhen>

Package Explorer IStructuredSelection

The Package Explorer is a mixture of org.eclipse.core.resources.IResource, org.eclipse.jdt.core.IJavaElement and other classes. If you are trying to find all of the *.java files, you would need to:

1. Iterate through the default variable
2. adapt the selection elements to your class, in this case IResource
3. use one of the org.eclipse.core.resources property testers to test the IResource property

For example:

<activeWhen>
    <iterate>
       <adapt type="org.eclipse.core.resources.IResource">
          <test property="org.eclipse.core.resources.name" 
                value="*.java"/>
       </adapt>
    </iterate>
</activeWhen>

Active editor type

If you want your handler to be active for a specific type of editor, you can use activeEditorId to target your handler.

<activeWhen>
    <with variable="activeEditorId">
       <equals value="org.eclipse.ui.DefaultTextEditor"/>
    </with>
</activeWhen>

Complex nested boolean expressions

You can also write complex nested boolean expressions, like (a & b & (c | d | (!e))):

<and>
  <test args="a" property="rcpAuthActivitiesExample.test" />
  <test args="b" property="rcpAuthActivitiesExample.test" />
  <or>
    <test args="c" property="rcpAuthActivitiesExample.test" />
    <test args="d" property="rcpAuthActivitiesExample.test" />
    <not>
      <test args="e" property="rcpAuthActivitiesExample.test" />
    </not>
  </or>
</and>

You can build the complete boolean expression out of arbitrary single boolean expressions. Not only property testers like in this example.

New Core Expressions in 3.3

In 3.3 there were 2 additions to the core expressions framework.

count and iterate

Count and iterate have always worked against java.util.Collection. The <count/> and <iterate> elements can now be used on any variable that adapts to org.eclipse.core.expressions.ICountable and org.eclipse.core.expressions.IIterable or implements the interfaces directly. It wasn't possible to use the java 1.5 constructs for iterable.

The workbench provides an adapter for ISelection and IStructuredSelection.

definitions

The org.eclipse.core.expressions.definitions extension point was introduced. You can create core expression definitions, and then reference them from other core expressions.

<extension point="org.eclipse.core.expressions.definitions">
    <definition id="org.eclipse.ui.examples.contributions.view.inView">
       <with variable="activePartId">
          <equals value="org.eclipse.ui.examples.contributions.view"/>
       </with>
    </definition>
</extension>

Then:

<activeWhen>
    <reference definitionId="org.eclipse.ui.examples.contributions.view.inView"/>
</activeWhen>

The referenced expression will be evaluated at this point.