Implementing MVP on a single activity with two (or

问题:

I'm developing a small application that shows a list, and when an item is clicked it opens a secondary screen with the item details. I want to implement MVP as my architecture for this app, and i have been struggling figuring out how to do that when I have a single activity with 2 fragments.

Some questions came up as when an item from the list is clicked, a callback is sent to the first presenter, but at this point, who is in charge of opening the second fragment? do the presenters 'talk' to each other? should i do it through the activity?

Been looking around for examples of single activity with multiple fragments implementing MVP, but couldn't find something like that yet.

(Yes, it can be done otherwise, but the purpose of the app is to learn implementing MVP on a single activity with multiple fragments)

Appreciate any help! Thanks!

回答1:

There are possibly many ways to implement MVP. Majorly we use 3 things. - View - Presenter - Modal

you should be clear with your working of screen before creating these things.

eg if you want a login screen. create structure (using interface) of activity first. like what your presenter and view will contain eg.

public interface LoginPresenter {
    void validateCredentials(String username, String password);
    void onDestroy();
}

View structure:

public interface LoginView {
void showProgress();

void hideProgress();

void setUsernameError();

void setPasswordError();

void navigateToHome();
}

Now these are the classes you need to implement on your view class (Activity/fragment) and presenter where your logic part resides.

Now about your queries.

which means the activity will have both presenters instances. No, your activity should not require to have multiple presenter. it already has opened fragment reference (by findfragmentby id or tag).

who is in charge of opening the second fragment?

you can open it from any of them either Activity/fragment. if Activity use getfragmentsupportManager if fragment use getfragmentManager

NOTE: For more info follow this git example. https://github.com/antoniolg/androidmvp

回答2:

After looking into different existing MVP sample projects I've decided to follow most of the concepts in the 'TODO-MVP-TABLET' git project by Google which can be found here:

https://github.com/googlesamples/android-architecture/tree/dev-todo-mvp-tablet

I've chosen this solution due to the level of abstraction and the ability to later on reuse any fragment in other activities without changing any code.

Solution principles:

• Each fragment has a presenter defined by an interface.
• There is a bigger presenter implementing all the smaller presenters.
• The bigger presenter holds references to all of the smaller presenters and when a method is invoked it simply delegates the action to the relevant presenter.
• Fragments are given the 'big' presenter as their presenter without actually being aware this is the case.
• Smaller presenters should hold the reference to the view.

Diagram taken from Google's github page:

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Update: Link isn't valid, seems like Google removed the project from their samples. Will leave it in case they reupload it.