LifecycleFragment | A library simplify fragment 's lifecycle | Dependency Injection library

Before you are using a callback which attaches to Activity which is considered as a container.
That callback is a middle man between two Fragments. The bad things about this previous solution are:

• Activity has to carry the callback, it means a lot of work for Activity.
• Two Fragments are coupled tightly, it is difficult to update or change logic later.

With the new ViewModel (with support of LiveData), you have an elegant solution. It now plays a role of middle man which you can attach its lifecycle to Activity.

• Logic and data between two Fragments now lay out in ViewModel.
• Two Fragment gets data/state from ViewModel, so they do not need to know each other.
• Besides, with the power of LiveData, you can change detail Fragment based on changes of master Fragment in reactive approach instead of previous callback way.

You now completely get rid of callback which tightly couples to both Activity and related Fragments.
I highly recommend you through Google's code lab. In step 5, you can find an nice example about this.

You are creating a new MutableLiveData instance each time you are calling getBooks

Hence your observer is not observing the right LiveData anymore.

To solve this

1. Your ViewModel should keep only one (immutable) LiveData instance

2. That immutable LiveData instance could either be:

   • A MediatorLiveData, which source is the repository's LiveData
   • A transformation of the repository's LiveData

That implies the repository method getBooks is only called once on initialization of the ViewModel, and that either refreshes itself OR you have to call another method on the repository to trigger a refresh.

Writing an answer for better discussion.

So I have (in Kotlin, sry) a model that is a list of notes (it’s just a sandbox app to play w/all this) and here’s my architecture: I don’t have a Repo, but I have Activity -> ViewModel -> Dao.

So Dao exposes a LiveData>

The LifecycleFragment and LifecycleActivity are currently not fully implemented. Those classes will be implemented when the lib is reaching 1.0-release. Currently you can use those LifecycleRegistry to observe LiveData objects. Those objects are based on a future result which could e.g. be an object from your database.

The official documentation can be found here: https://developer.android.com/topic/libraries/architecture/index.html

Official statement regarding the two classes you mentioned:

Lifecycle Fragment and ActivityCompat in the Support Library do not yet implement LifecycleOwner interface. They will when Architecture Components reaches 1.0.0 version.

I SOLVED THIS!!! When I creating my ViewModel class, I pass "this" 1-st parameter into method

buyViewModel = ViewModelProviders.of(**this**, viewModelFactory).get(BuyViewModel.class);

But I need pass "getActivity()", and code looks like that

buyViewModel = ViewModelProviders.of(**getActivity()**,viewModelFactory).get(BuyViewModel.class);

The comment from CommonsWare and the link to the bug solve this question. For standard fragment you need trigger yourself the corresponding lifecycle events, e.g., lifecycleRegistry.handleLifecycleEvent(Lifecycle.Event.ON_PAUSE);

when I tried to implements the LiveData Class and it required the permission checking in onActive() function

No, it does not. What you are seeing is a Lint warning, which you can suppress. What is required is that you hold the permission before attempting to use this particular bit of LiveData.

Is there any way to move such onRequestPermissionsResult() and checkSelfPermission() functions to the LocationListener ?

No.

Answer to Question No. 1:

It seems, that you are observing the wrong LiveData by creating new Instances of your LiveData every time you update your LiveData in your ViewModel. You must return the same Instance of LiveData to be able to observe it and to check if it has Observers.

For example in your ViewModel:

After consulting with the Android team we figured out that it is indeed an issue within the SupportFragmentManager which is solved in v 26.+ so switching to