Hi, I am using a View Model to pass some values ba...

# getting-started

[Nat Strangerweather]

Hi, I am using a View Model to pass some values based on user clicks. It is working great apart from one thing: my initial default Int in the View Model cannot be 0, because if I use 0, the app resets when I first open it and click on a button. For my initial value I need this code:

val notificationManager: NotificationManager =
        context.getSystemService(NOTIFICATION_SERVICE) as NotificationManager

But I read that using a context in a View Model is the wrong approach. Is there a solution to this?

[Dinorah Tovar]

I do believe that using Context in a ViewModel is not a nice a pattern but, there’s a solution using AndroidViewModel that has a context that will not cause a Memory leak.
This may help u

class yourViewModel (application: Application) : AndroidViewModel(application) {

    private val context = getApplication<Application>().applicationContext

}

[Nat Strangerweather]

Interesting, thanks for this! 🙂👍

[Dinorah Tovar]

For welcome.

[Nat Strangerweather]

@Dinorah Tovar I'm getting this error: "Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference". I put this in my main page:

@Composable
fun MainInterface(viewModel: MainAndroidViewModel = MainAndroidViewModel(application = Application ())) {}

[Nat Strangerweather]

Is it the correct way of initialising it?

[Ian Lake]

You should be using = viewModel() to get ViewModel instances in Compose (also, feel free to check out #compose): https://developer.android.com/jetpack/compose/interop#viewmodel

[Nat Strangerweather]

Worked perfectly, thanks!

[FunkyMuse]

@Ian Lake if the composable is used in an activity, viewModel() returns the same instance until the activity is finished or the process is killed.

Is there a way to scope a viewmodel to a composable?

Let's say we take fragments out of the equation, single activity + composables, means every viewmodel that's instantiated will be scoped to the activity lifecycle?

[Ian Lake]

There's no ability to scope ViewModels to an arbitrary Composable elements (that's being tracked in https://issuetracker.google.com/issues/165642391), but if you're using Navigation Compose (https://developer.android.com/jetpack/compose/navigation) then ViewModels are automatically scoped to each individual composable screen when you use the viewModel() API