Kotlin Android Studio

1. get websocket kotlin android

 package com.example.alarmcyrpto

import android.os.Bundle
import android.util.Log
import android.widget.EditText
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import com.google.gson.Gson
import com.google.gson.annotations.SerializedName
import okhttp3.*

class MainActivity : AppCompatActivity() {

    private lateinit var okHttpClient: OkHttpClient
    private lateinit var webSocket: WebSocket
    private lateinit var gson: Gson
    private lateinit var btcPriceTv: TextView
    private lateinit var pilihCoinEditText: EditText
    private var currentSymbol: String = "btcusdt"

    private lateinit var textViewCurrentPrice: TextView
    private lateinit var textViewTargetPrice: TextView
    private var currentPrice: Double = 0.0
    private var targetPrice: Double = 0.0

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

        textViewCurrentPrice = findViewById(R.id.textViewCurrentPrice)
        textViewTargetPrice = findViewById(R.id.textViewTargetPrice)

        okHttpClient = OkHttpClient()
        gson = Gson()
        btcPriceTv = findViewById(R.id.textView6)
        pilihCoinEditText = findViewById(R.id.pilihCoin)

        // setup websocket connection with default symbol
        val request = Request.Builder().url("wss://fstream.binance.com/ws/$currentSymbol@ticker").build()
        webSocket = okHttpClient.newWebSocket(request, object : WebSocketListener() {
            override fun onOpen(webSocket: WebSocket, response: Response) {
                Log.d("TAG", "WebSocket opened")
            }

            override fun onMessage(webSocket: WebSocket, text: String) {
                super.onMessage(webSocket, text)
                runOnUiThread {
                    val tickerData = gson.fromJson(text, TickerData::class.java)
                    btcPriceTv.text = tickerData.lastPrice
                    Log.d("TAG", text)
                }
            }

            override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) {
                Log.e("TAG", "WebSocket error: ${t.message}")
            }
        })

        pilihCoinEditText.setOnEditorActionListener { _, _, _ ->
            currentSymbol = pilihCoinEditText.text.toString()
            webSocket.cancel()
            val newRequest = Request.Builder().url("wss://fstream.binance.com/ws/$currentSymbol@ticker").build()
            webSocket = okHttpClient.newWebSocket(newRequest, object : WebSocketListener() {
                override fun onOpen(webSocket: WebSocket, response: Response) {
                    Log.d("TAG", "WebSocket opened")
                }

                override fun onMessage(webSocket: WebSocket, text: String) {
                    super.onMessage(webSocket, text)
                    runOnUiThread {
                        val tickerData = gson.fromJson(text, TickerData::class.java)
                        btcPriceTv.text = tickerData.lastPrice
                    }
                }

                override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) {
                    Log.e("TAG", "WebSocket error: ${t.message}")
                }
            })
            false
        }

        private fun updatePrice(currentPrice: Double, targetPrice: Double) {
            this.currentPrice = currentPrice
            this.targetPrice = targetPrice
            textViewCurrentPrice.text = currentPrice.toString()
            textViewTargetPrice.text = targetPrice.toString()
        }

        private val broadcastReceiver = object : BroadcastReceiver() {
            override fun onReceive(context: Context?, intent: Intent?) {
                val currentPrice = intent?.getDoubleExtra("current_price", 0.0) ?: 0.0
                val targetPrice = intent?.getDoubleExtra("target_price", 0.0) ?: 0.0
                updatePrice(currentPrice, targetPrice)
            }
        }

        override fun onResume() {
            super.onResume()
            val filter = IntentFilter("com.example.alarmcyrpto.UPDATE_PRICE")
            registerReceiver(broadcastReceiver, filter)
        }

        override fun onPause() {
            super.onPause()
            unregisterReceiver(broadcastReceiver)
        }
    }

    override fun onDestroy() {
        super.onDestroy()
        webSocket.cancel()
    }
}

data class TickerData(
    @SerializedName("c")
    val lastPrice: String
)

2. alarm main activity jika close tidak aktif

package com.example.alarmcyrpto

import android.app.NotificationChannel
import android.app.NotificationManager
import android.content.Context
import android.os.Build
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.core.app.NotificationCompat
import androidx.core.app.NotificationManagerCompat
import java.util.*
import android.widget.TextView

class MainActivity : AppCompatActivity() {

    private val binanceApiService = BinanceApiService.create()

    private val notificationChannelId = "BinanceAlarmNotificationChannel"
    private val notificationChannelName = "BinanceAlarmNotification"
    private val notificationId = 1

    private val symbol = "BTCUSDT"
    private val targetPrice = 28033.0

    private lateinit var btcPriceTv: TextView

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

        createNotificationChannel()

        getPrice()
        startAlarm()
    }

    private fun getPrice() {
        binanceApiService.getPrice(symbol) { price ->
            runOnUiThread {
                btcPriceTv = findViewById(R.id.tv_price)
                btcPriceTv.text = price
                val currentPrice = price.substringAfter(": ").toDoubleOrNull()
                if (currentPrice != null && currentPrice >= targetPrice) {
                    showNotification()
                }
            }
        }
    }

    private fun startAlarm() {
        Timer().scheduleAtFixedRate(object : TimerTask() {
            override fun run() {
                getPrice()
            }
        }, 0, 5000)
    }

    private fun showNotification() {
        val notificationBuilder = NotificationCompat.Builder(this, notificationChannelId)
            .setSmallIcon(R.drawable.ic_notification)
            .setContentTitle("BinanceAlarm")
            .setContentText("$symbol price has reached $targetPrice")
            .setPriority(NotificationCompat.PRIORITY_DEFAULT)

        with(NotificationManagerCompat.from(this)) {
            notify(notificationId, notificationBuilder.build())
        }
    }

    private fun createNotificationChannel() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            val channel = NotificationChannel(
                notificationChannelId,
                notificationChannelName,
                NotificationManager.IMPORTANCE_DEFAULT
            )
            channel.description = "BinanceAlarm notification channel"
            val notificationManager =
                getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
            notificationManager.createNotificationChannel(channel)
        }
    }

}

3. cara agar runing program tanpa buka aplikasi 
val intent = Intent(this, AlarmService::class.java)
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
    startForegroundService(intent)
} else {
    startService(intent)
}

4. tampilkan ke xml 
val textView = findViewById<TextView>(R.id.textView)
textView.text = "Current price is: $currentPrice"

5. jika runing background threadui
runOnUiThread {
    val textView = findViewById<TextView>(R.id.textView)
    textView.text = "Current price is: $currentPrice"
}

6. get api service
import com.google.gson.Gson
import okhttp3.*
import java.io.IOException

class BinanceApiService(private val client: OkHttpClient) {

    interface BinanceApiService {
        // ...
        @GET("/api/v3/ticker/price")
        fun getPrice(@Query("symbol") symbol: String): Call<String>
        // ...
    }

    companion object {

        private const val BASE_URL = "https://fapi.binance.com"

        fun create(): BinanceApiService {
            val client = OkHttpClient.Builder().build()
            return BinanceApiService(client)
        }
    }

    private val gson = Gson()

    fun getPrice(symbol: String, callback: (String) -> Unit) {
        val url = "$BASE_URL/fapi/v1/ticker/price?symbol=$symbol"
        val request = Request.Builder().url(url).build()

        client.newCall(request).enqueue(object : Callback {
            override fun onFailure(call: Call, e: IOException) {
                callback("Error: ${e.message}")
            }

            override fun onResponse(call: Call, response: Response) {
                if (response.isSuccessful) {
                    val body = response.body?.string()
                    if (body != null) {
                        val price = gson.fromJson(body, Price::class.java).price
                        callback("$symbol : $price")
                    } else {
                        callback("Error: response body is null")
                    }
                } else {
                    callback("Error: ${response.message}")
                }
            }
        })
    }

    private data class Price(
        val price: String
    )
}