Commands¶

Commands are used to declare desired behaviour (ie Show would be a command). They can be organized into categories (like Navigation).

Implementations for your commands are called handlers, the handler used may be context sensitive:

• Show command on the Map Editor may zoom out to show all the layers
• Show command on the Layer View may zoom out to show the selected layer
• Show command on the Table View may zoom out to show the current selection

Commands can get a bit more fancy:

• You can use categories to organize your commands
• You can use parameters (this is how the “Show View” command is implemented once and configured to show multiple views.

Related Information:

• org.eclipse.ui.commands extension point
• platform command framework in the eclipse wiki
• Basic workbench extension points using commands in the PDE programmers guide.

Creating a new Command using the Extension Point:

<extension
      point="org.eclipse.ui.commands">
   <category
         description="Actions that change what is shown"
         id="org.locationtech.udig.navigation"
         name="Navigation">
   </category>
   <command
         categoryId="org.locationtech.udig.navigation"
         description="Show all content"
         id="org.locationtech.udig.show"
         name="Show All">
   </command>
</extension>

Creating a new Command using Java:

ICommandService cmdService =
  (ICommandService) getSite().getService(ICommandService.class);

Category navigation =
  cmdService.getCategory("org.locationtech.udig.navigation");

if (!navigation.isDefined()) {
  navigation.define("Navigation", "Actions that change what is shown");
}

Command show =
  cmdService.getCommand("org.locationtech.udig.show");

if (!show.isDefined()) {
  show.define("Show", "Show content on screen", navigation);
}

To get the workbench ICommandService:

public class StartupOperations implements IStartup {
    public void earlyStartup(){
       IWorkbench workbench = PlatformUI.getWorkbench();
       ICommandService cmdService = (ICommandService) workbench.getService( ICommandService.class );
       ...
    }
}

Handlers¶

Handlers are an implementation of a command. Several handlers may be defined for a given command - choosing which one is active is the fun part.

You can define an activeWhen expressions in order to make your handler context sensitive.

A handler is chosen based on several bits of magic:

• Variables used in activeWhen expressions are compared; the handler with the most specific variables is chosen
• Default Handler (ie one with no conditions) is used as the last resort.

Figuring out if the Handler is Enabled

• You can also define an expression to enabled or disable the handler.

The variables used in the activeWhen and enabledWhen expressions come from