Asynchronous call in Kotlin not working with RecycleView - json

Question

I'm struggling with asynchronous calls - the app is just crashing. I want to load a JSON-file (containing 100 JSON-objects) from an URL and then send it to RecyclerView.
Here is the MainActivity-class:
class MainActivity : AppCompatActivity() {
lateinit var recyclerView: RecyclerView
lateinit var linearLayoutManager: LinearLayoutManager
private val url = [//some address here]
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
recyclerView = findViewById<RecyclerView>(R.id.recyclerView)
recyclerView.layoutManager = linearLayoutManager
AsyncTaskHandler().execute(url)
}
inner class AsyncTaskHandler : AsyncTask<String, String, String>() {
override fun onPreExecute() {
super.onPreExecute()
}
override fun doInBackground(vararg url: String?): String {
val text: String
val connection = URL(url[0]).openConnection() as HttpURLConnection
try {
connection.connect()
text = connection.inputStream.use { it.reader().use {reader -> reader.readText()} }
} finally {
connection.disconnect()
}
return text
}
override fun onPostExecute(result: String?) {
super.onPostExecute(result)
handleJson(result)
}
}
private fun handleJson(jsonString: String?) {
val jsonArray = JSONArray(jsonString)
var list = mutableListOf<DataSet>()
var i = 0
while (i < jsonArray.length()) {
val jsonObject = jsonArray.getJSONObject(i)
list.add(DataSet(
jsonObject.getString("title"),
jsonObject.getString("type")
))
i++
}
val adapter = Adapter(list)
recyclerView.adapter = adapter
}
}
...and ListAdapter-class:
class Adapter (private var targetData: MutableList<DataSet>): RecyclerView.Adapter<ViewHolder>() {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val v = LayoutInflater.from(parent.context).inflate(R.layout.element, parent, false)
return ViewHolder(v);
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
val item = targetData[position]
holder.title?.text = item.title
holder.type?.text = item.type
}
override fun getItemCount(): Int {
return targetData.size
}
}
class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
var title = itemView.findViewById<TextView>(R.id.itemTitle)
var type = itemView.findViewById<TextView>(R.id.itemType)
}
What might be the problem here? Is there any better option to perform this?