CODEWITHSUNDEEP
androidandroid-livedataandroid-viewmodel
yazan sayed
yazan sayed

Reputation: 1139

Using LiveData in ViewModel to pass object to other activity

I'm trying to pass data from MainActivity to SecondActivity using a MutableLiveData in a ViewModel,, the following code gives me a NullPointerException when SecondActivity tries to access the LiveData

ViewModel:

class MyViewModel: ViewModel() {
val current=MutableLiveData<String>()
}

Main Activity:

class MainActivity : AppCompatActivity() {
private val viewModel: MyViewModel by lazy {
        ViewModelProviders.of(this).get(MyViewModel::class.java)
    }

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    textView.text="test"
    viewModel.current.value="test"
    textView.setOnClickListener {
        startActivity(Intent(this,SecondActivity::class.java))
    }
}}

SecondActivity:

class SecondActivity: AppCompatActivity() {
private val viewModel: MyViewModel by lazy {
    ViewModelProviders.of(this).get(MyViewModel::class.java)
}

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_second)
    textView2.text = viewModel.current.value!! // NullPointerException
}}

Upvotes: 0

Views: 1439

Answers (1)

Francesc
Francesc

Reputation: 29280

The viewmodel in your second Activity is not the same as that on the 1st Activity; there is a cache of ViewModels by owner (the activities in this case), and these owners are different in each case.

ViewModels can be used to share data between Fragments on the same Activity, but they don't work for sharing data between activities. For that, pass the data in the Intent to start the 2nd Activity (if lightweight), otherwise store it in some long lived object.

val intent = Intent(this,SecondActivity::class.java).apply {
    putExtra("KEY", "<string to pass here>")
}
startActivity(intent)

Upvotes: 2

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