GWT displaying widgets with asynchronous calls on RootPanel

Question

I am having problems while adding my widget into the RootPanel of another container class. I think that it may be related to the Asynchronous call that I make during the creation of the widget. I have a main class named ImageView which implements EntryPoint. In this class, I am creating an instance of my widget named NewWidget by clicking on a button. However, I cannot display it with the traditional methods:

Here is the EntryPoint class (ImageView):

import com.mycompany.project.client.widgets.NewWidget;
public class ImageViewer implements EntryPoint {

public void onModuleLoad() {

    Button b = new Button("Button");
    RootPanel.get().add(b);

    b.addClickHandler(new ClickHandler() {
        public void onClick(ClickEvent event) {
            NewWidget w = new NewWidget();
            RootPanel.get().add(w);
        }
    });
}

And here is my widget (NewWidget):

public class NewWidget extends Composite {

     final static DataServiceAsync service = (DataServiceAsync) GWT.create(DataService.class);

     final FlowPanel mainPanel = new FlowPanel();

     public NewWidget() {
         fillImagePath();
     }

     public void fillImagePath(){
     ServiceDefTarget endpoint = (ServiceDefTarget) service;
     endpoint.setServiceEntryPoint(GWT.getModuleBaseURL() + "data");
         service.getAllDocuments(new AsyncCallback<ArrayList<String>>() {
             @Override
             public void onFailure(Throwable e) {
                 Window.alert("Server call failed.");
             }
             @Override
             public void onSuccess(ArrayList<String> paths) {
                 process(paths);
             }
         });
     }

     public void process(ArrayList<String> paths){
         ArrayList<String> imagePath = paths;
         Image img = new Image(imagePath.get(4));
         mainPanel.add(img);
         initWidget(mainPanel);
     }
}

In this NewWidget, I am making an asynchronous call to my server in order to receive a String ArrayList, which contains 10 Strings that refer to the file path of 10 different images (i.e, "images/01.jpg", "images/02.jpg", and so on). I am pretty sure that I successfully and correctly receive these image paths. I have arbitrarily chosen index number 4 to display in my NewWidget.

The problem is that I cannot display this NewWidget in my ImageView main panel. I can easily display other widgets with this method. With many attempts, I have realized that I can display the image if I add the line RootPanel.get().add(mainPanel) at the end of NewWidget. However, I do not want to make a call that refers to the parent container (RootPanel in ImageView). Why can't I display this image with only instantiating it in my container panel, like I can display any other widget? I am pretty sure that it is related to the Asynchronous call not getting completed before I attempt to add the widget. But I don't know how to fix this.

I would be very glad if people would share their ideas. Thanks.

Tyson · Accepted Answer · 2011-04-26 22:19:13Z

1

Move the initWidget(mainPanel) call to the first line the constructor.

answered Apr 26, 2011 at 22:19

Tyson

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