Eclipse 4.4.0 – Tool bar item visibility based on the currently active perspective

Displaying trimmed window tool bar items based on the currently active perspective in an Eclipse 4.4.0 RCP application would seem like a straightforward task but it actually involves a fair bit of tinkering and there are a few not so obvious pitfalls along the way.

After reading section 31.2 of Lars Vogel’s Eclipse 4 RCP tutorial the obvious approach was to associate a ‘visible-when’ expression with each of my perspective-specific tool bar items. The first problem I encountered was the fact that expressions are not evaluated for items added directly to the main tool bar (see Bug 400217). By ‘added directly’ I mean added as children of the tool bar element in the e4xmi application model. Luckily, when added as ToolBar Contributions visible-when expressions are evaluated as expected.

The next problem I encountered was how to determine the currently active perspective from within a visible-when expression. I couldn’t find any up to date documentation regarding the names of predefined context variables and none of the variables listed in Command Core Expressions were available in my Eclipse Luna 4.4.0 RCP application. To determine which context variables were available I added the following @CanExecute method to one of my tool bar item command handlers:

@CanExecute
public boolean canExecute(final IEclipseContext ictx) {
    final EclipseContext ctx = (EclipseContext) ictx.getParent();
    System.out.println("### START ###");
    for (final Entry<String, Object> entry : ctx.localData().entrySet()) {
        System.out.println(String.format("Key: '%s', value: '%s'", entry.getKey(), entry.getValue()));
    }
    System.out.println("### END ###");
    return true;
}

The following entry was included in the output from this method:

 Key: 'org.eclipse.e4.ui.model.application.ui.advanced.MPerspective', value: 'org.eclipse.e4.ui.model.application.ui.advanced.impl.PerspectiveImpl@2d778add (elementId: my.example.perspective.Edit, tags: [], contributorURI: platform:/plugin/my.example.application) (widget: Composite {}, renderer: org.eclipse.e4.ui.workbench.renderers.swt.PerspectiveRenderer@7fc44dec, toBeRendered: true, onTop: false, visible: true, containerData: null, accessibilityPhrase: null) (label: Edit, iconURI: null, tooltip: , context: PerspectiveImpl (my.example.perspective.Edit) Context, variables: [])'

Based on this output I wrote the following following Property Tester to query the elementId of the active perspective:

/**
 * Property tester that checks the <code>elementId</code> of the currently active perspective
 */
public class PerspectivePropertyTester extends PropertyTester {

    /**
     * @param receiver the currently active {@link MPerspective}
     * @param property the property to test, in this case 'elementId'
     * @param args additional arguments, in this case an empty array
     * @param expectedValue the expected value of {@link MPerspective#getElementId()}
     */
    @Override
    public boolean test(final Object receiver, final String property, final Object[] args, final Object expectedValue) {
        final MPerspective perspective = (MPerspective) receiver;
        return perspective.getElementId().equals(expectedValue);
    }
}

This was then configured in plugin.xml as follows:

<?xml version="1.0" encoding="UTF-8"?>
<plugin>
   ...
   <extension point="org.eclipse.core.expressions.propertyTesters">
      <propertyTester class="my.example.application.propertytester.PerspectivePropertyTester"
            id="my.example.application.propertytester.PerspectivePropertyTester"
            namespace="my.example.property"
            properties="perspectiveId"
            type="org.eclipse.e4.ui.model.application.ui.advanced.MPerspective">
      </propertyTester>
   </extension>
   <extension point="org.eclipse.core.expressions.definitions">
      <definition id="my.example.expression.isEditPerspective">
         <with variable="org.eclipse.e4.ui.model.application.ui.advanced.MPerspective">
            <test forcePluginActivation="true"
                  property="my.example.property.perspectiveId"
                  value="my.example.perspective.Edit">
            </test>
         </with>
      </definition>
      <definition id="my.example.expression.isPreviewPerspective">
         <with variable="org.eclipse.e4.ui.model.application.ui.advanced.MPerspective">
            <test forcePluginActivation="true"
                  property="my.example.property.perspectiveId"
                  value="my.example.perspective.Preview">
            </test>
         </with>
      </definition>
   </extension>
   ...
</plugin>

As a footnote I should also note that subscribing to UIEvents.UILifeCycle.PERSPECTIVE_OPENED events does not work as expected (see Bug 408681) so the above approach is probably the best option. You could, of course, set the visibility of tool bar items programmatically when switching perspective but this is far from ideal.

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Posted in Eclipse RCP
2 comments on “Eclipse 4.4.0 – Tool bar item visibility based on the currently active perspective
  1. Roland says:

    Thank you very much for this short tutorial – it really saved my day 🙂

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