GWT：在视图展示位置之间传递数据

Question

I have a view impl say SampleView.java.I have a table in my view.When a row is clicked, a new place is passed to the place controller like,

placeController.goto(new ScreenPlace()) ;

Now the issue is, i need to pass some data from SampleView to ScreenPlace , so that i can use that data in the ScreenView.Data is basically a MAP of key value pair which i need to pass from SampleView to ScreenView via ScreenPlace.Or in other words, how can i transfer data from one view to another view.How can i do this?.I'm a newbie to GWT.Please help!.

Answer 1

There are basically two ways to solve this problem:

1. Pass the data via an EventBus : You can create an Event (ie LoadSampleDataEvent ) that you pass the data to and fire in on the global EventBus . Because you will have a reference to the global EventBus in your ScreenPlace you will be able to handle the Event there and display it in the corresponding view.

2. Encode the data in your URL : You will probably have an URL associated with your ScreenPlace (ie http://myHost/#screen ). You can encode some unique identifier of your data in that url http://myHost/#screen?id=1 or http://myHost/#screen/1 ). Then in your ScreenPlace you can parse the id parameter from the URL and retrieve the data. You will probably need to pass the map that contains the data to your ScreenPlace . This can be done via an Event on the EventBus or a global Singleton instance.

I would recommend the second appraoch, as it makes your ScreenPlace "stateless" and boomarkable. A user can just open the URL (ie http://myHost/#screen?id=10 ) and your ScreenPlace will show the detailed view.

For that to work you must handle the case when the map hasn't been loaded yet (for example if the user directly navigates to the corresponding URL and not through your table first).

Answer 2

Handler Interface:


import com.google.gwt.event.shared.EventHandler;

public interface MessageTransferHandler extends EventHandler
 {
    public void onMessageTransfer(MessageTransferEvent event);
}

Event Class:



import com.google.gwt.event.shared.GwtEvent;

public class MessageTransferEvent extends GwtEvent<MessageTransferHandler>{

    String message;
    int flag;

    public MessageTransferEvent(String message,int flag)
    {
        this.message=message;
        this.flag=flag;
    }
    public String getMessage()
    {
        return message;
    }

    public int getFlag()
    {
        return flag;
    }
    public static Type<MessageTransferHandler> TYPE=new Type<MessageTransferHandler>();
    @Override
    public com.google.gwt.event.shared.GwtEvent.Type<MessageTransferHandler> getAssociatedType() {
        return TYPE;
    }

    @Override
    protected void dispatch(MessageTransferHandler handler) {
        handler.onMessageTransfer(this);
    }

}