MainActivity.kt

class MainActivity : AppCompatActivity() {
    // Reference to the RecyclerView adapter
    private lateinit var adapter: PartAdapter
  
    private fun loadPartsAndUpdateList() {
        // Launch Kotlin Coroutine on Android's main thread
        GlobalScope.launch(Dispatchers.Main) {
            // Execute web request through coroutine call adapter & retrofit
            val webResponse = WebAccess.partsApi.getPartsAsync().await()

            if (webResponse.isSuccessful) {
                // Get the returned & parsed JSON from the web response.
                // Type specified explicitly here to make it clear that we already
                // get parsed contents.
                val partList : List<PartData>? = webResponse.body()
                Log.d(tag, partList?.toString())
                // Assign the list to the recycler view. If partsList is null,
                // assign an empty list to the adapter.
                adapter.partItemList = partList ?: listOf()
                // Inform recycler view that data has changed.
                // Makes sure the view re-renders itself
                adapter.notifyDataSetChanged()
            } else {
                // Print error information to the console
                Log.d(tag, "Error ${webResponse.code()}")
                Toast.makeText(this@MainActivity, "Error ${webResponse.code()}", Toast.LENGTH_SHORT).show()
            }
        }
    }
    
    // For reference: shortened code of onCreate. See the full example on Github for
    // commented code.
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        // rv_parts is the recyclerview UI element in the XML file
        rv_parts.layoutManager = LinearLayoutManager(this)
        // Create the adapter for the recycler view, which manages the contained items
        adapter = PartAdapter(listOf(), { partItem : PartData -> partItemClicked(partItem) })
        rv_parts.adapter = adapter
        // Start loading recycler view items from the web
        loadPartsAndUpdateList()
    }
    
    // ...
}