Using MVP with GWT2.7

[Richa Kulkarni]

Is it mandatory to have a separate Handler and Event class for every event while trying t use the event bus? Can i not use a single class for all the events?

How can I do this? Any sample code will be greatly appreciated.

TIA.

[N Troncoso]

You could technically do that, but you'd need some way to differentiate between events; Maybe with an enum:

public class MyEvent extends GwtEvent<MyEvent.Handler>

{

    public static enum EventTypes

    {

        THIS_EVENT,

        THAT_EVENT;

    };

    

    public interface Handler extends EventHandler

    {

        void onDispatch(MyEvent event);

    }

    public static final GwtEvent.Type<Handler> TYPE = new GwtEvent.Type<>(); // NOSONAR

    private final EventTypes type;

    public MyEvent(EventTypes type)

    {

        this.type = type;

    }

    @Override

    public GwtEvent.Type<Handler> getAssociatedType()

    {

        return TYPE;

    }

    

    public EventTypes getType()

    {

        return type;

    }

    @Override

    protected void dispatch(Handler handler)

    {

        handler.onDispatch(this);

    }

}

I don't think this is a very good approach, though, as you lose the ability to pass specific parameters based on that particular kind of event.

[Richa]

Thanks Troncoso.

I get what you say, and agree that its not a very good approach.

But my concern is, For a huge application having around 200 events . Will I have to write 200 Event handlers, 200 Event Classes and Event types ?

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[Juan Pablo Gardella]

It's old, but check the comments at http://wanderingcanadian.ca/2010/11/05/hello-mvp-with-gin/

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[Collins, Pablo]

Hi Richa,

Have you looked at EventBinder?

https://github.com/google/gwteventbinder

Pablo

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[Jens]

I get what you say, and agree that its not a very good approach.

But my concern is, For a huge application having around 200 events . Will I have to write 200 Event handlers, 200 Event Classes and Event types ?

There is https://github.com/google/gwteventbinder which avoids defining handlers by using annotations. Then there is https://github.com/ekuefler/gwt-supereventbus which pretty much works the same as Guava's EventBus in terms of event types and listening for events. It also has some other interesting features and provides an adapter so you can use SuperEventBus together with GWT classes that require GWT's EventBus.

-- J.

[Frank Hossfeld]

You can try mvp4g. (http://mvp4g.github.io/mvp4g/) Using mvp4g, the events are defined in a interface.  

[Gourab Panda]

Improvising Noah code to send different Data as well.

public class MyEvent<T> extends GwtEvent<MyEvent.Handler>

{

    public static enum EventTypes

    {

        THIS_EVENT,

        THAT_EVENT;

    };

    

    public interface Handler<T> extends EventHandler

    {

        void onDispatch(MyEvent<T> event);

    }

    public static final GwtEvent.Type<Handler> TYPE = new GwtEvent.Type<>(); // NOSONAR

    private final EventTypes type;

    private T result;

    

    public MyEvent(EventTypes type, T result)

    {

        this.type = type;

        this.result = result;

    }

    @Override

    public GwtEvent.Type<Handler> getAssociatedType()

    {

        return TYPE;

    }

    

    public EventTypes getType()

    {

        return type;

    }

    @Override

    protected void dispatch(Handler handler)

    {

        handler.onDispatch(this);

    }

    /**

     *

     * @return result

     */

    public T getResult() {

        return result;

    }

}