Android LiveData - how to reuse the same ViewModel on different activities?

Question

Example ViewModel:

public class NameViewModel extends ViewModel {
    // Create a LiveData with a String
    private MutableLiveData mCurrentNa         


        

Answer 1

Simply create the instance of your ViewModel, in this case NameViewModel

Your ViewModel Factory be like

class ViewModelFactory : ViewModelProvider.NewInstanceFactory() {

    override fun  create(modelClass: Class) =
        with(modelClass){
            when {
                isAssignableFrom(NameViewModel::class.java) -> NameViewModel.getInstance()
                else -> throw IllegalArgumentException("Unknown viewModel class $modelClass")
            }
        } as T


    companion object {
        private var instance : ViewModelFactory? = null
        fun getInstance() =
            instance ?: synchronized(ViewModelFactory::class.java){
                instance ?: ViewModelFactory().also { instance = it }
            }
    }
}

And your ViewModel

class NameViewModel : ViewModel() {

    //your liveData objects and many more...

    companion object {
        private var instance : NameViewModel? = null
        fun getInstance() =
            instance ?: synchronized(NameViewModel::class.java){
                instance ?: NameViewModel().also { instance = it }
            }
    }
}

Now you can use ViewModelProviders to get the same instance of your ViewModel to use in any activity

ViewModelProviders.of(this, ViewModelFactory.getInstance()).get(NameViewModel::class.java)

OR

create an extension function for easier access

fun  AppCompatActivity.getViewModel(viewModelClass: Class) =
    ViewModelProviders.of(this, ViewModelFactory.getInstance()).get(viewModelClass)