Main Activity of our Bitcoin Android App with Kotlin on the SSaurel's Blog

MainActivity.kt

package com.ssaurel.bitcoinpricewatcher

import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.view.Menu
import android.view.MenuItem
import android.view.View
import kotlinx.android.synthetic.main.activity_main.*
import okhttp3.*
import org.json.JSONObject
import java.io.IOException

class MainActivity : AppCompatActivity() {

  // We will use the Coin Desk API to get Bitcoin price
  val URL = "https://api.coindesk.com/v1/bpi/currentprice.json"
  var okHttpClient: OkHttpClient = OkHttpClient()

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

  override fun onCreateOptionsMenu(menu: Menu?): Boolean {
    menuInflater.inflate(R.menu.main, menu)
    return super.onCreateOptionsMenu(menu)
  }

  override fun onOptionsItemSelected(item: MenuItem): Boolean {
    when(item.itemId) {
      R.id.load -> {
        loadBitcoinPrice()
        return true
      }
    }

    return super.onOptionsItemSelected(item)
  }

  private fun loadBitcoinPrice() {
    progressBar.visibility = View.VISIBLE

    val request: Request = Request.Builder().url(URL).build()
    okHttpClient.newCall(request).enqueue(object : Callback {
      override fun onFailure(call: Call?, e: IOException?) { }

      override fun onResponse(call: Call?, response: Response?) {
        val json = response?.body()?.string()
        // we get the json response returned by the Coin Desk API
        // make this call on a browser for example to watch the properties
        // here we get USD and EUR rates properties
        // we split the value got just to keep the integer part of the values
        val usdRate = (JSONObject(json).getJSONObject("bpi").getJSONObject("USD")["rate"] as String).split(".")[0]
        val eurRate = (JSONObject(json).getJSONObject("bpi").getJSONObject("EUR")["rate"] as String).split(".")[0]

        runOnUiThread {
          progressBar.visibility = View.GONE
          bitcoinValues.text = "$$usdRate\n\n$eurRate€"
        }
      }
    })
  }

}