On 27 août, 17:15, "[email protected]" <[email protected]>
wrote:
> Hi all.
>
> I've been trying to use the UIBinder, i like it a lot. At the same
> time i've replaced my own MVP implementation with gwt-presenter (which
> is cleaner than what i had), but there's one bit i can't figure out by
> myself regarding dependency injection with GIN.
>
> I have a MainPresenter which is retrieved by the injector interface
> after i instantiate the injector. This one instantiates the
> corresponding MainView using DI, and the actual layout is defined in a
> UiBinder xml file. This works fine, until i try to add another of my
> View objects into the MainView UiBinder file. Something like:
> <gwt:UiBinder xmlns:ui="urn:ui:com.google.gwt.uibinder"
> ...
> xmlns:stats="urn:import:my.package.for.statistics">
> ...
> <stats:StatsView ui:field="statsView"/>
> ...
> </gwt:UiBinder>
>
> One question and one issue.
>
> 1) How do you instantiate your Presenter objects? I have a
> StatsPresenter for the StatsView, but if i simply use the UiBinder
> like in here, it will never be instantiated. I've 'fixed' this by
> adding a reference to this StatsPresenter from the MainPresenter -
> which is injected - but only so that one is created, it's not like i
> need that reference there.
If your presenter has no public method of any kind (i.e. a
StatsPresenter instance has to exist, but nothing will actually do
anything with it; e.g. it just listens to events from the view and
fire events on the event bus and/or listens to events from the
eventBus and updates the view accordingly), then maybe you can reverse
the dependency and have StatsView instantiate its StatsPresenter and
keep a reference to it in a private field (StatsPresenter would still
be an independent class that could be tested without StatsView and
with mock StatsPresenter.Display instead); this would make StatsView a
"simple" Composite widget (that happens to use MVP but this becomes an
implementation detail).
Did I correctly understand your problem?
> 2) Given my solution above, i need to make sure that the StatsView is
> a singleton, otherwise the Presenter instantiates a new StatsView
> which is different from the one created by the UiBinder.
Er, I don't understand...
> Again i try
> to use dependency injection by defining in the MainView a StatsView
> field as in:
>
> @UiField(provided=true)
> StatsView statsView;
If StatsView has dependencies that should be injected view GIN in its
constructor then yes, that the way to go
> I then add in my injector:
> bind(StatsView.class).in(Singleton.class);
See above, I don't understand why it has to be a singleton (actually,
I believe it shouldn't)
> but either this or using a Provider method instead gives me the
> following:
> 00:01:18.766 [ERROR] Failed to create an instance of 'MainView' via
> deferred binding java.lang.NullPointerException: null at
> com.google.gwt.user.client.ui.ComplexPanel.add(ComplexPanel.java:77)
> at com.google.gwt.user.client.ui.VerticalPanel.add(VerticalPanel.java:
> 53) at
> ...
>
> Any hints on this? I can't figure out what i'm doing wrong.
Have you assigned a StatsView instance to your statsView field? When
using @UiField(provided=true), you're telling UiBinder to not
instantiate a StatsView but instead use the one you're providing; i.e.
UiBinder will read the field value and use that to build the UI
instead of building the UI and write the field's value with the widget
it instantiated.
Have a look at the examples on the UiBinder wiki page, section
named... "Using a widget that requires constructor args" (sic!)
http://code.google.com/p/google-web-toolkit-incubator/wiki/UiBinder#Using_a_widget_that_requires_constructor_args
(the @UiFactory method –first example, without method arguments– would
allow you to use a Provider<StatsView> for instance and have the
factory return provider.get(); this would be handy when you need to
have several StatsView instances in the same .ui.xml)
(@UiConstructor, or the @UiFactory with arguments, wouldn't fit with
DI via GIN, as the values come from the ui.xml itself)
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