Observe LiveData instance in fragment and activity

Question

I have a simple scenario where I do something in fragment and when I receive the LiveData I want to do something in Activity.

ViewModel:

class MyViewModel(application: Application) : AndroidViewModel(application) {
    
   ...
    
    fun getUser(id: String): LiveData<User> {
        return repository.getUser(id)
    }
}

Fragment:

class MyFragment : Fragment() {

    private lateinit var myViewModel: MyViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        activity?.run {
            myViewModel = ViewModelProviders.of(this).get(MyViewModel::class.java)
        } ?: throw Exception("Invalid Activity")
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        return inflater.inflate(R.layout.fragment, container, false)
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        button.setOnClickListener {
            showProgressBar()
            myViewModel.getUser(editText.text.toString()).observe(this, Observer { it ->
                //TODO
            })
        }
    }
}

Activity:

class MainActivity : AppCompatActivity() {

    private lateinit var myViewModel: MyViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        myViewModel = ViewModelProviders.of(this).get(MyViewModel::class.java)
        //Here I would like to observe the user instance returned from the getUser() method
    }
}

So the issue I'm having is that I would like to have an instance of LiveData<User> in MyViewModel so that I could observe it in Activity and Fragment. How can I achieve this?

You can share the ViewModel between the activity and fragment....pass parent activity instance to ViewModelProviders.of() in your fragment (or even better use sharedViewModel if using Koin!) — John O'Reilly
– John O'Reilly, Commented Mar 13, 2019 at 10:44
I think I'm doing that already, the this instance that I'm passing to ViewModelProviders.of() is the activity itself — Nelson Almendra
– Nelson Almendra, Commented Mar 13, 2019 at 10:53
Save user data from FragmentViewModel to database .Define another viewModel for your activity and subscribe your Activity to observe changes in this database . I think this will be much more cleaner to implement and understand @NelsonAlmendra — Ayush Bansal
– Ayush Bansal, Commented Mar 25, 2019 at 18:44

Abd Nezar · Accepted Answer · 2022-01-15 02:27:17Z

15

In Fragemnts (as best practice) Should Use

viewModel.userLiveData.observe(viewLifecycleOwner, Observer {
    //your code here
})

In Activity Use

viewModel.userLiveData.observe(this, Observer {
        //your code here
    })

answered Jan 15, 2022 at 2:27

Abd Nezar

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Comments

Sam Rendal · Accepted Answer · 2019-03-13 10:56:42Z

4

in class MyViewModel create

    val userLiveData =MutableLiveData<User>()

and getter

    fun getUserLiveData(id: String): MutableLiveData<User> {
            return userLiveData
    }

    fun getUser(id: String){
    val disposableUser = repository.getUser(id)
    .subscribe({
        userLivedata.postValue(it)
    })

}

And in activity or Fragment called

   myViewModel.getUserLiveData.observe(this, Observer { it ->
      //TODO
    })
   myViewModel.getUser(...)

And Now in ViewModel you have object User (userLiveData.getValue())

answered Mar 13, 2019 at 10:56

Sam Rendal

411 bronze badge

Comments

Valgaal · Accepted Answer · 2019-03-13 10:59:38Z

1

Write method in Activity doSomethingWithUser(user: User)

And in your livedata

myViewModel.getUser(editText.text.toString()).observe(this, Observer { it ->
            (requireActivity() as MainActivity).doSomethingWithUser(it)
        })

answered Mar 13, 2019 at 10:59

Valgaal

95610 silver badges27 bronze badges

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