How do I initialize viewmodel in addedditactivity, is there a better alternative?

Question

I have this database that contains information about celebrities, lots of information, ie movies, roles, articles...

Without the viewmodel, all of the stuff in the edit text gets lost. So i dont want to lose all of that info on rotation.

So i send an intent with all the relevant info of a selected celebrity(sql room) to the addeditactivity, so now how do i initialize the viewmodel? If I do getStringExtra in onCreate, wouldn't that just rewrite the viewmodel again when the activity gets recreated?

how do i get around this, also is there a better alternative? im a beginner, thanks in advance!

@Override
protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_main);
   // ......... shared preferences code .................
   // get intent code ................

   mViewModel = ViewModelProviders.of(this).get(testViewModel.class);
   mViewModel.celebName = intent.getStringExtra(CELEB_NAME);
   // similar..........
  
}

please include all relevant code into your question – a_local_nobody Oct 27 '20 at 11:52 — a_local_nobody, Oct 27 '20 at 11:52

Leontsev Anton · Answer 1 · 2020-10-27T12:12:40.773

You can initialize your viewModel in onCreate() using ViewModelFactory to pass your data from getStringExtra to your viewModel. Use viewModelFactory pattern to pass data to your viewModel. Here "YourINFOParameter" is your data from getStringExtra. So after initialization in your viewModel you have set parameter you can observe using liveData. I am suing Kotlin in answer.

as example:

override fun onCreateView(
........
     val viewModelFactory =
            TestViewModelFactory(
                yourINFOparameter,
                application)

val testViewModel = ViewModelProvider(
            this, viewModelFactory
        ).get(TestViewModel::class.java)
.................

Then declare class TestViewModelFactory:

class TestViewModelFactory(
private val yourINFOparameter: String, private val application: Application) : ViewModelProvider.Factory {
    @Suppress("unchecked_cast")
    override fun <T : ViewModel?> create(modelClass: Class<T>): T {
        if (modelClass.isAssignableFrom(TestViewModel::class.java)) {
            return TestViewModel(yourINFOparameter,
            application) as T
        }
        throw IllegalArgumentException("Unknown ViewModel class")
    }
}

And your viewModelclass:

class TestViewModel(yourINFOparameter: String, application: Application) : AndroidViewModel(application) {

............................}

check it in java https://stackoverflow.com/questions/51829280/how-to-use-a-viewmodelprovider-factory-when-extends-from-androidviewmodel — Leontsev Anton, Oct 29 '20 at 14:57

score 0 · Answer 2 · answered Oct 27 '20 at 12:12

0

No, ViewModels have separate lifecyles from Activities. When your Activity gets rotated/recreated it will still use your previously-instantiated ViewModel (and any data saved in it) unless it has already been cleared.

See https://developer.android.com/topic/libraries/architecture/viewmodel

If the activity is re-created, it receives the same MyViewModel instance that was created by the first activity. When the owner activity is finished, the framework calls the ViewModel objects's onCleared() method so that it can clean up resources.

answered Oct 27 '20 at 12:12

Thomas Lee

71
1
3

what about mViewModel.celebName = intent.getStringExtra(CELEB_NAME) in onCreate, it doesn't overwrrite the viewmodel value after rotation? – Absolute Oct 27 '20 at 12:20
Absolute, you can make this way but it is kind of hodgie code – Leontsev Anton Oct 27 '20 at 13:04
It will override the value if you set it during onCreate. You should try and instantiate ViewModel values in the ViewModel itself. – Thomas Lee Oct 27 '20 at 13:32

How do I initialize viewmodel in addedditactivity, is there a better alternative?

2 Answers2