<@UFX608MK7> What about a ViewModel property that ...

# compose

[streetsofboston]

@Cody Engel What about a ViewModel property that is of a type of a @Model class?

[Cody Engel]

Yeah that’s what I currently have, my team would probably kick me off the team if this ever made it onto master though 😅

abstract class ComposeViewModel<T> : ViewModel() {
    // This should return a class annotated with @Model
    abstract val model: T
}

@Model
data class Name(var name: String = "Android")

class NameViewModel : ComposeViewModel<Name>() {
    override val model: Name = Name()
}

[streetsofboston]

You can always send your resume to me! 😄

[streetsofboston]

But, seriously, wouldn't this be a good 'work-around' since inheritance with @Model won't work?

[Cody Engel]

It solves my immediate problem for sure. Moving to Compose though I’d like to be done with LiveData though

[Cody Engel]

Today we do the stuff Jetpack Compose does behind the scenes by hand with LiveData and it ultimately just gets kind of messy with more complex models

[streetsofboston]

Does that ViewModel property of the @Model type need to be held by a LiveData type? I haven't tried it, but couldn't the ViewModel just instantiate a proper val instance of that @Model type and have the ViewModel's methods modify that property's properties (that are observed by the @Model annotation)?

[Cody Engel]

Nope, no LiveData is required with this solution. The value survives state changes and it updates whenever it’s updated as well.

[Cody Engel]

This is a very simple example but I really like how it ends up reading overall, being able to annotate a ViewModel with @Model would just round things out I think…

abstract class ComposeViewModel<T> : ViewModel() {
    // This should return a class annotated with @Model
    abstract val model: T
}

@Model
data class Name(var name: String = "Android")

class NameViewModel : ComposeViewModel<Name>() {
    override val model: Name = Name()
}

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val viewModel = ViewModelProviders.of(this).get(NameViewModel::class.java)
        setContent {
            HelloForm(viewModel.model)
        }
    }
}

@Composable
fun HelloForm(name: Name) = MaterialTheme {
    Column(modifier = Spacing(16.dp)) {
        Greeting(name = name.name)
        TextField(
            value = name.name,
            onValueChange = {
                name.name = it
            }
        )
        Button(text = "New Name")
    }
}

@Composable
fun Greeting(name: String) {
    Text(text = "Hello $name!", modifier = Spacing(top = 16.dp, bottom = 16.dp))
}

[Cody Engel]

…Also the Button no longer does anything 😅

[streetsofboston]

I agree it would be nicer to be able to annotate the actual ViewModel with @Model.
Say, in your onValueChange you'd wan to invoke a method on your ViewModel (not just change the Name's name); then you'd have to pass both the ViewModel and its @Model property into the HelloForm() function or just pass the ViewModel and always write viewModel.name to access the @Model instance...

[Luca Nicoletti]

Why do you need a ViewModel in the first place?

[streetsofboston]

To be able to use a ViewModelProvider 😀
To make sure the state survives a config change.

[Luca Nicoletti]

Compose should handle it

[streetsofboston]

'Should' or 'will'? 😀
I haven't gotten a confirmation on that nor found documentation on that....

[Cody Engel]

Compose does not handle that.

[Cody Engel]

And yes Anton, that’s a good point that I didn’t point out. Only passing the LiveData would not be enough, you’d want to call functions directly on the view model