MVVM on Android
Notes: 10. Challenge: Create a ViewModel
The clearAllCreatures() method in the AllCreaturesViewModel class uses Kotlin Coroutine and would look like this:
fun clearAllCreatures() = viewModelScope.launch { repository.clearAllCreatures() }
Also AppCompatResources is preffered over context.getDrawable() as the IDE recommends you to do this.
So the code to set the avatarListItem image in the bind() method of the ViewHolder class would be:
binding.avatarListItem.setImageDrawable(
AppCompatResources.getDrawable(
binding.avatarListItem.context,
creature.drawable
)
)
Your next challenge is to put together all you’ve learned so far to build a view model for the app’s first screen that should show the list of all creatures in the repository.
AllCreaturesActivity is setup already with a RecyclerView and adapter.
You’ll need to update the view holder in CreatureAdapter used for the rows of the RecyclerView to display
the data for each creature.
In your view model, create a LiveData object for a List of creatures that AllCreaturesActivity will observe
and in the observer, call updateCreatures() on the RecyclerView adapter.
As part of this challenge, you also want to implement the clear all creatures capability in the app menu. Pause the video and take a shot at building out AllCreaturesViewModel and connecting it to AllCreaturesActivity. When you’re ready, unpause to see my solution.
First we add AllCreaturesViewModel to the view model package, and put a repository property in its constructor.
class AllCreaturesViewModel(private val repository: CreatureRepository = RoomRepository()) : ViewModel() {
}
We extend the ArchitectureComponent ViewModel class. Next we add an allCreaturesLiveData property, and set it equal to the result from calling getAllCreatures() on the repository.
We also add a getter for the LiveData.
private val allCreaturesLiveData = repository.getAllCreatures()
fun getAllCreaturesLiveData() = allCreaturesLiveData
We add a function to clear all creatures in the repository, which we’ll call when the user chooses the option in the menu.
fun clearAllCreatures() = repository.clearAllCreatures()
In AllCreaturesActivity, we add a viewmodel property.
private lateinit var viewModel: AllCreaturesViewModel
And we connect to the viewmodel in onCreate() by using a call to ViewModelProviders.
viewModel = ViewModelProviders.of(this).get(AllCreaturesViewModel::class.java)
In onCreate(), we also setup the observer on the all creatures LiveData. In the observer we update the recyclerview adapter.
viewModel.getAllCreaturesLiveData().observe(this, Observer { creatures ->
creatures?.let {
adapter.updateCreatures(creatures)
}
})
In onOptionsItemSelected for the menu, we call the method on the view model to clear all creatures.
viewModel.clearAllCreatures()
Finally, in the view holder of CreatureAdapter, we populate the viewholder itemView with data from the creature in the row.
itemView.avatarListItem.setImageDrawable(itemView.context.getDrawable(creature.drawable))
itemView.name.text = creature.name
itemView.hitPoints.text = creature.hitPoints.toString()
Now we build and run the app. And sure enough, we see the creatures we’ve added previously displayed in the RecyclerView.We can also add a new creature. And it gets added the list straight away.
We can choose the menu option, and all creatures are removed from the repository.