On Wednesday, May 14, 2014 11:57:34 AM UTC+2, wahaha wrote:
should the View object keep a reference to the corresponding Activity
object(which act as a presenter)?
in the demo called helloMVP provided by the gwt official site,it does.
but in my humble opinion,Presenter is the layer on top of View.and the
upper layer may invocate the lower layer,but the lower layer shoudn't
invocate the upper layer.
so,i think the view object shoundn't keep a reference to the activity
object.
It depends how you implement MVP wrt listening to events: is the presenter
pulling widgets from the view to attache event handlers to them (or
possibly attach them through specialized methods on the view, e.g.
addSubmitButtonClickHandler vs. getSubmitButton().addClickHandler) or is it
implementing a callback interface that is passed to the view (so the
addClickHandler is done in the view, possibly through UiBinder, and simply
delegates to the appropriate method of the presenter interface, e.g.
presenter.onSubmitButtonClicked()).
But in any case, the view keeps one (or several) reference(s) to the
presenter, either directly or indirectly through event handlers.
You might argue that the presenter might not directly implement the
callback interface, but it's exactly the same, just with an additional
level of indirection: the view (or its widgets) has to call back to the
presenter when the user interacts with it, so it must keep a reference to
it.
You could use an event bus to decouple things, but that's using a
sledgehammer to crack a nut; you'll pay it in performance and
maintainability: it's not because you split the view and the presenter that
they're decoupled. The main reason for using MVP is to be able to mock the
view and avoid using a GWTTestCase to test the presenter (and you can test
it at a slightly higher level, e.g. show error on field rather than put
error message in panel, show panel and add error style to field).
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