#Kotlin Android Demos for building android apps with kotlin.

ListView

A list view with BaseAdapter as its adapter. And handle list item click handler.

class CelebrityAdapter(var celebrityList: Array<Celebrity>, val context: Context) : BaseAdapter() {
    override fun getView(position: Int, convertView: View?, parent: ViewGroup?): View {
      var view: View? = null
      val viewHolder: ListRowHolder
      if (convertView == null) {
        view = LayoutInflater.from(context).inflate(R.layout.list_item, parent!!, false) as View
        viewHolder = ListRowHolder(view)
        view.tag = viewHolder
      } else {
        view = convertView
        viewHolder = view.tag as ListRowHolder
      }

      viewHolder.titleTextView.text = celebrityList.get(position).name
      viewHolder.subtitleTextView.text = celebrityList.get(position).twitter

      return view
    }

    override fun getItem(position: Int): Any {
      return celebrityList.get(position)
    }

    override fun getItemId(position: Int): Long {
      return position.toLong()
    }

    override fun getCount(): Int {
      return celebrityList.size
    }
  }

  private class ListRowHolder(row: View?) {
    public val titleTextView: TextView
    public val subtitleTextView: TextView

    init {
      this.titleTextView = row?.findViewById(R.id.textView) as TextView
      this.subtitleTextView = row?.findViewById(R.id.subtitleTextView) as TextView
    }
  }
}

Customized BaseAdapter CelebrityAdapter. Optimize the list view performance with a Row Holder ListRowHolder.

Handler

  private var _handler: Handler = object : Handler() {
    override fun handleMessage(msg: Message) {
      if(msg.what == 0x123) {
        // do something
      }
    }
  }

Every 200 ms, send a message to handler:

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_handler)

    Timer().schedule(object : TimerTask() {
      override fun run() {
        _handler.sendEmptyMessage(0x123)
      }
    }, 0, 200)
  }

OK Http

You can do http request with okHttp library. It also brings Connection Pool and cache, Gzip, etc. It helps improve http requests. You can do sync and async http requests with okHttp.

Sync request

class SyncActivity : AppCompatActivity(), View.OnClickListener {
  private val TAG = SyncActivity::class.java.simpleName

  private var _startButton: Button? = null
  private var _textView: TextView? = null

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_sync)

    _startButton = findViewById(R.id.startButton) as Button
    _textView = findViewById(R.id.textView) as TextView
    _startButton!!.setOnClickListener(this)
  }

  override fun onClick(v: View?) {
    var okHttpTask = OKHttpTask(_textView!!)
    okHttpTask.execute("https://api.github.com/")
  }

  open class OKHttpTask(textView: TextView) : AsyncTask<String, Void, String>() {
    var client = OkHttpClient()
    private var httpTextView: TextView? = textView

    override fun doInBackground(vararg params: String?): String {
      var builder = Request.Builder()
      builder.url(params[0])
      var request = builder.build()

      try {
        var response = client.newCall(request).execute()
        return response.body().string()
      } catch (e: Exception) {
        e.printStackTrace()
      }

      return ""
    }

    override fun onPostExecute(result: String?) {
      super.onPostExecute(result)
      httpTextView!!.text = result
    }
  }
}