I’m trying to use ViewModel + LiveData, as seen <https://developer.android.com/jetpack/compose/inter...

# compose

[Brett Best]

I’m trying to use ViewModel + LiveData, as seen https://developer.android.com/jetpack/compose/interop#viewmodel however the code sample (in thread reply) always shows null

[Brett Best]

@Composable
fun LegalBodyContent(contentPadding: InnerPadding = InnerPadding(), onLegal: () -> Unit) {
  val viewModel: MyViewModel = viewModel()
  val user = viewModel.user.observeAsState()
  Text(text = "${user.value}")
}


class MyViewModel: ViewModel() {
  private val userId: LiveData<String> = MutableLiveData()
  val user = userId.switchMap { id ->
    liveData {
      while(true) {
        emit("Test string")
        delay(30_000)
      }
    }
  }
}

[satyan]

Do you set userId value anywhere ?

[Brett Best]

I thought that emit("Test string") , would set it?

[satyan]

With switchMap you are mapping the value received in userId to whatever livedata returned in the block

[Brett Best]

Right and that doesn’t happen on the initial initialization

[Brett Best]

So to kick off say a network request, would I need to use onCommit to then call a method on the view model to do that?

[satyan]

If there's not value in userId, you won't map anything and thus won't have anything in user

[satyan]

It depends where you're getting the userId from.

[Brett Best]

At the moment I’m using a single activity for the entire UI of my app using https://github.com/zsoltk/compose-router

[satyan]

Ask yourself the right questions:
- How can I get my current userId ?
- With this userId how can I get my user ?

I'm not sure you need to use a livedata for the userId. You could just use val user = livedata{}

And load and emit your user inside the livedata block.

[Brett Best]

Ah sorry, what I was aiming to do was to load data (using Fuel) in a few of my compose functions that represent different screens. A lot of the examples I saw used multiple activities.

[satyan]

If you just want to learn and play with compose maybe find some simpler use cases. The codelabs are good starting points.

You can also take a look at Google samples (or any other sample you can find in this channel) if you need help with your app architecture.

[Brett Best]

I think the Android Compose examples (on Github) all used either multiple activities / fragments. Thanks for your help 🙂