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