Android Kotlin: How to get Battery Percentage Programmatically

This code snippet demonstrates how to retrieve the current battery percentage programmatically in an Android application written in Kotlin. It utilizes the Android Broadcast system to listen for changes in battery level and update a TextView accordingly.

Explanation:

  1. Broadcast Receiver:
    • The code defines a custom BroadcastReceiver subclass. This receiver will be notified whenever the battery level changes on the device.
  2. Intent Filter:
    • An IntentFilter object is created to specify the type of broadcasts the receiver is interested in. In this case, it filters for broadcasts with the action Intent.ACTION_BATTERY_CHANGED.
  3. Registering Receiver:
    • Inside the onCreate method of the MainActivity, the registerReceiver method is called to register the custom broadcast receiver with the system. The IntentFilter object is passed as an argument to specify the type of broadcasts it should listen for.
  4. Updating Text View:
    • When the battery level changes, the onReceive method of the broadcast receiver is called.
    • Inside this method, the currentBatteryCharge extension property of the received Intent is used to retrieve the battery percentage.
    • Finally, the retrieved percentage is displayed on a TextView with the ID textView in the layout.
  5. Extension Property:
    • The code defines an extension property for the Intent class named currentBatteryCharge.
    • This property retrieves the raw battery level (EXTRA_LEVEL) and scale (EXTRA_SCALE) values from the BatteryManager extras within the intent.
    • It then calculates the percentage by dividing the level by the scale and multiplying by 100.

Summary

By combining the broadcast receiver and the extension property, this code efficiently obtains the current battery percentage and displays it on the screen whenever the battery level changes. It provides a clear and concise approach to programmatically access battery information in an Android application using Kotlin.


MainActivity.kt 

package com.example.jetpack

import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.content.IntentFilter
import android.os.BatteryManager
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*


class MainActivity : AppCompatActivity() {

    // initialize a new broadcast receiver instance
    private val receiver:BroadcastReceiver = object: BroadcastReceiver(){
        override fun onReceive(context: Context?, intent: Intent?) {
            intent?.apply {
                textView.text = "Current battery charge\n$currentBatteryCharge%"
            }
        }
    }

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

        // initialize a new intent filter instance
        val filter = IntentFilter(Intent.ACTION_BATTERY_CHANGED)

        // register the broadcast receiver
        registerReceiver(receiver,filter)
    }
}



// extension property to get current battery charge percentage from intent
val Intent.currentBatteryCharge:Float
    get() {
        // integer containing the maximum battery level
        val scale = getIntExtra(
            BatteryManager.EXTRA_SCALE, -1
        )

        //  integer field containing the current battery
        //  level, from 0 to EXTRA_SCALE
        val level = getIntExtra(
            BatteryManager.EXTRA_LEVEL, -1
        )

        // return current battery charge percentage
        return level * 100 / scale.toFloat()
    }
activity_main.xml 

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/constraintLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#EDEAE0"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:fontFamily="sans-serif-condensed"
        android:gravity="center"
        android:padding="32dp"
        android:textColor="#0014A8"
        android:textSize="35sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.25"
        tools:text="TextView" />

</androidx.constraintlayout.widget.ConstraintLayout>
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