Proper way to access ViewModel from Recyler Adaper

Question

I have a Data Repository that saved data & fetches data, this is passed into a ViewModel as constructor. I have methods in a ViewModel that fetches and saves data.

I have a button that I click for each row (Item in a RecyclerView list) this saves data using the ViewModel.

I have found that I can directly call a ViewModel initialised it into the constructor, I checked the Google Android examples & this part is not covered.

Something like this below: Copied from: Databinding Recyclerview and onClick

private ExampleViewModel exampleViewModel;

public ExampleListAdapter(Context context, List<Model> models) {
        this.context = context;
        this.models = models;

        // ...
        exampleViewModel = ViewModelProviders.of((FragmentActivity) context).get(ExampleViewModel.class);
}

But then, I could also call a ViewModel by passing a ViewModel object from the Activity alongside with the context.

So what the proper way of calling a ViewModel?

Answer 1

This is your pojo class

data class Item(val id: Int)

This is your adapter.

class Adapter : RecyclerView.Adapter<Adapter.ViewHolder>() {

    var items: List<Item> = emptyList()
        set(value) {
            field = value
            notifyDataSetChanged()
        }

    var callback: Callback? = null

    override fun getItemCount(): Int {
        return items.size
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val itemView = LayoutInflater.from(parent.context)
            .inflate(R.layout.simple_textview, parent, false)
        return ViewHolder(itemView)
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val item = items[position]
        holder.itemView.setOnClickListener {
            callback?.onItemClicked(item)
        }
        holder.bindItem(item)
    }

    inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {

        fun bindItem(item: Item) {
            // Fill layout
        }
    }

    interface Callback {
        fun onItemClicked(item: Item)
    }
}

This is your viewModel class.

class MyViewModel : ViewModel(), Adapter.Callback {

    override fun onItemClicked(item: Item) {

    }
}

And this is your fragment.

class MyFragment : Fragment() {

    private val adapter = Adapter()

    private lateinit var myViewModel: MyViewModel


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        myViewModel = ViewModelProviders.of(activity!!).get(MyViewModel::class.java)
        adapter.callback = myViewModel
    }

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.my_fragment, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        adapter.items = listOf(
            Item(1),
            Item(2)
        )

        //Setup recyclerView etc.
    }
}