13. Handler

Handler

Nalu supports handlers. A handler behaves like a controller, but has no visual component. A Handler can only be triggered by an event. The following instances will be injected in a handler:

• context
• event bus
• router

Nalu will create handlers at application start. To trigger a handler, an event has to be fired.

Defining a Handler

To create a handler, you have to:

• extend AbstractHandler
  • C: type of the context

By extending AbstractHandler you will have access to the allowing instances:

• C context: instance of the application context (Singleton)
• event bus: instance of the application wide event bus
• router: instance of the router

To tell Nalu, that this class is a handler, you have to annotate the class with Handler. Nalu will automatically create an instance for each class annotated with @Handler at application start.

A handler requires a

• a public, zero-argument constructor
• annotate the handler with @Handler

Here is an example of a handler:

@Handler
public class MyHandler
  extends AbstractHandler<MyApplicationContext> {

  public MyHandler() {
  }

  @Override
  public void bind() {
    this.eventBus.addHandler(MyEvent.TYPE,
                             e -> {
                               // your code here
                             });
  }
}