GIN injection failure

Question

I am using google-gin in my application and it works fine except from one case and I don't understand why. Basically, I inject a toolbar widget I created into my view and it works fine. I see my toolbar with all the different buttons but when I click on the Home button, I have a NullPointerException which means the eventBus is null and therefore the injection in HomeButton did not work.

My view:

public MyView extends AbstractView{
    @Inject
    EditorToolbar toolbar; 
    // ...
}

My Toolbar widget:

public class EditorToolbar extends HorizontalLayoutContainer {
    private HomeButton homeBtn;
    private ToolbarIconButton saveButton;

    private final static int BUTTON_RIGHT_MARGIN=5;

    public EditorToolbar() {
        homeBtn = new HomeButton();
        saveButton = new ToolbarIconButton("Save",AppImages.INSTANCE.saveBW());

        this.add(homeBtn, new HorizontalLayoutData(-1, -1, new Margins(0, BUTTON_RIGHT_MARGIN, 0, 0)));
        this.add(saveButton, new HorizontalLayoutData(-1, -1, new Margins(0, BUTTON_RIGHT_MARGIN, 0, 0)));
    }

    public HandlerRegistration addSaveHandler(SelectEvent.SelectHandler handler){
        return saveButton.addSelectHandler(handler);
    }
}

The button where the injection of eventBus does not work:

public class HomeButton extends ToolbarIconButton {

    @Inject
    private MetadataEditorEventBus eventBus;

    public HomeButton() {
        super("Back to home page", AppImages.INSTANCE.home());
        setToolTip("Navigate back to the home page");
        setWidth(130);
        bindUI();
    }

    private void bindUI() {
        addSelectHandler(new SelectEvent.SelectHandler() {
            @Override
            public void onSelect(SelectEvent selectEvent) {
                eventBus.fireBackToHomePageEvent();
            }
        });
    }
}

My GIN module:

public class MetadataEditorGinModule extends AbstractGinModule {

    @Override
    protected void configure() {
        bind(com.google.web.bindery.event.shared.EventBus.class).to(MetadataEditorEventBus.class);
        // bind(com.google.gwt.event.shared.EventBus.class).to(MetadataEditorEventBus.class);
        bind(MetadataEditorEventBus.class).in(Singleton.class);

        bind(com.google.web.bindery.requestfactory.shared.RequestFactory.class).to(MetadataEditorRequestFactory.class);

        bind(com.google.gwt.place.shared.PlaceController.class).toProvider(PlaceControllerProvider.class).in(Singleton.class);

        bind(ActivityDisplayer.class).to(MetadataEditorAppDisplayer.class).in(Singleton.class);
        bind(MetadataEditorAppView.class).in(Singleton.class);
    }
}

Does anybody know why I can't get this to work?

Do you have any Guice modules that are playing around with MetadataEditorEventBus? — Chetan Kinger, Apr 09 '15 at 16:53

André · Accepted Answer · 2015-04-09T17:14:45.737

1

You're instantiating the HomeButton widget, this way you're not using GIN and will fail to inject anything.

You will have to also inject the HomeButton instance on your EditorToolbar. Since the HomeButton is required (not a optional injection), add to the constructor.

@Inject
public EditorToolbar(HomeButton homeButton) {
    homeBtn = homeButton;
    //... rest of the code as usual.
}

edited Apr 09 '15 at 17:14

answered Apr 09 '15 at 17:07

André

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Thank you. But I don't understand why I have to inject homeButton in the constructor and not as a field... I tried it but it did not work. – ovie Apr 09 '15 at 17:16
You can inject, but you're missing the @Inject annotation :-) – André Apr 09 '15 at 17:22
No I tried it and it did not work. An exceptions was raised. I don't remember the exact exception but it tells "deferring dinding...". Well thanks anyway – ovie Apr 09 '15 at 18:54

GIN injection failure

1 Answers1