how to inject a uiBinder with @Inject (instead of GWT.create())?

Question

Firstly, is doing such thing a good practice ? I tried what seems to be the right way for me but wasn't successful :

public class FormViewImpl extends CompositeView implements HasUiHandlers<C>, FormView {
    public interface SettlementInstructionsSearchFormViewUiBinder extends UiBinder<Widget, SettlementInstructionsSearchFormViewImpl> {}

    @Inject
    static FormViewImpl uiBinder;

    @Inject
    static Provider<DateEditorWidget> dateEditorProvider;

    @UiField(provided = true)
    MyComponent<String> myComp;

    @UiField
    DateEditorWidget effectiveDateFrom;

    // .. other fields

    @Inject
    public FormViewImpl () {
        myComp = new MyComponent<String>("lol");

        if (uiBinder == null)
            uiBinder = GWT.create(SettlementInstructionsSearchFormViewUiBinder.class);

        initWidget(uiBinder.createAndBindUi(this));
    }

    @UiFactory
    DateEditorWidget createDateEditor() {
        return dateEditorProvider.get();
    }
}

What other things than a class with no arguments is required ? In my company's project the same kind of code works at some other place. Sorry from the high level of noob here... If you guys had any pointers it would be nice.

Thanks

Answer 1

Two issues:

First, two of your @Inject fields are static - have you done anything to make static fields be injected? Static fields don't get set when Gin (or Guice) creates new instances, those have to be set once and done. As they are static, they will never be garbage collected - this may be okay with you, or it might be a problem, and you should change them to instance fields. If you want to keep them static, then you must invoke requestStaticInjection in your module to ask Gin to initialize them when the ginjector is created.

Next, if you do choose to remove static, the uiBinder field must still be null in that constructor, because the fields can't have been injected yet! How do you set a field on an object that you haven't yet created? That's what you are expecting Gin to be able to do. Instead, consider passing that as an argument into the @Inject decorated constructor. You don't even need to save it as a field, since the widget will only use it the one time.

Answer 2

To have a class generated by GIN (doesn't matter if it is a uiBinder or not) it is not necessary for it to have a default constructor (i.e. the one without parameters). The class you want to inject must have the constructor annotated with @Inject:

@Inject
public InjectMeClass(Object a, Object b)

The other class which is injected, suppose it is a UiBinder, must have the injected fields annotated with @UiField(provided=true):

public class Injected extends Composite {

    private static InjectedUiBinder uiBinder = GWT
            .create(InjectedUiBinder.class);

    interface InjectedUiBinder extends UiBinder<Widget, Injected> {
    }

    @UiField(provided=true)
    InjectMeClass imc;

    public Injected(final InjectMeClass imc) {
        this.imc=imc;
        initWidget(uiBinder.createAndBindUi(this));
    }

So, back to your case:

    @UiField(provided = true)
    MyComponent<String> myComp;

    @Inject
    public FormViewImpl (MyComponent<String> myComp) {
        this.myComp = myComp;

and for example:

   public class MyComponent<T> extends Composite {
        private T value;

        @Inject
        public MyComponent(T t) {
            this.value = t;
            ...
        }
        ...
    }

In the GIN module you can have a provider:

    @Provides
    @Singleton
    public MyComponent<String> createMyComponent() {
        return new MyComponent<String>("lol");
    }