Android AlarmManager example with BroadcastReceiver

 1. Create a BroadcastReceiver for receiving the pending intent from AlarmManager.

import android.widget.Toast
import android.content.Intent
import android.content.BroadcastReceiver
import android.content.Context

class MyAlarmReceiver: BroadcastReceiver() {
    override fun onReceive(context: Context, intent: Intent) {
        Toast.makeText(context, "Alarm Triggered", Toast.LENGTH_LONG).show()
    }
}

2. Register the above BroadcastReceiver in the manifest file inside the application tag.

<receiver android:name=".MyAlarmReceiver"/>

3. Creating the alarm manager and starting it in an Activity.

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.app.AlarmManager
import android.content.Context
import android.app.PendingIntent
import android.content.Intent
import kotlinx.android.synthetic.main.activity_main.*
import java.util.*


class MainActivity: AppCompatActivity() {
    private val REQUEST_CODE = 100
    private lateinit var alarmManager: AlarmManager
    private lateinit var pendingIntent: PendingIntent

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        tv_current_time.text = Date().toString()

        // Creating the pending intent to send to the BroadcastReceiver
        alarmManager = getSystemService(Context.ALARM_SERVICE) as AlarmManager
        val intent = Intent(this, MyAlarmReceiver::class.java)
        pendingIntent = PendingIntent.getBroadcast(this, REQUEST_CODE, intent, PendingIntent.FLAG_UPDATE_CURRENT)

        // Setting the specific time for the alarm manager to trigger the intent, in this example, the alarm is set to go off at 23:30, update the time according to your need
        val calendar = Calendar.getInstance()
        calendar.timeInMillis = System.currentTimeMillis()
        calendar.set(Calendar.HOUR_OF_DAY, 23)
        calendar.set(Calendar.MINUTE, 30)

        // Starts the alarm manager
        alarmManager.setRepeating(
            AlarmManager.RTC,
            calendar.timeInMillis,
            AlarmManager.INTERVAL_DAY,
            pendingIntent
        )

    }

    override fun onDestroy() {
        super.onDestroy()
        // Cancels the pendingIntent if it is no longer needed after this activity is destroyed.
        alarmManager.cancel(pendingIntent)
    }
}