Time for action – calculating values on demand

The Eclipse context can supply not only services but also dynamically calculated values. These are supplied via an interface IContextFunction. By registering a service with that class name and a key name with the service.context.key, it is possible to create a value upon request.

1. Create a class called RandomFunction, which extends ContextFunction and which returns a random value:

   package com.packtpub.e4.application;
   import org.eclipse.e4.core.contexts.ContextFunction;
   import org.eclipse.e4.core.contexts.IEclipseContext;
   public final class RandomFunction extends ContextFunction {
     @Override
     public Object compute(final IEclipseContext context) {
       return Math.random();
     }
   }

2. To allow E4 to recognize the function, register an instance with the OSGi runtime. Although this could be done within the Activator, currently a service ordering bug prevents this from happening. Instead, register it using declarative services.

   Create a file called...