How to check if a bluetooth device is connected with an Android device using Kotlin?

This example demonstrates how to check if a Bluetooth device is connected with an Android device..

Step 1 − Create a new project in Android Studio, go to File ⇉ New Project and fill all required details to create a new project.

Step 2 − Add the following code to res/layout/activity_main.xml.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:orientation="vertical"
   android:padding="16dp">
   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Open bluetooth setting from your own device and check for better results."
      android:textAlignment="center"
      android:textColor="@android:color/background_dark"
      android:textSize="24sp"
      android:textStyle="bold" />
</LinearLayout>

Step 3 − Add the following code to src/MainActivity.kt

import android.bluetooth.BluetoothDevice
import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.content.IntentFilter
import android.os.Bundle
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
   override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      title = "KotlinApp"
      val filter = IntentFilter()
      filter.addAction(BluetoothDevice.ACTION_ACL_CONNECTED)
      filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECT_REQUESTED)
      filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECTED)
      this.registerReceiver(broadcastReceiver, filter)
   }
   private val broadcastReceiver: BroadcastReceiver = object : BroadcastReceiver() {
      var device: BluetoothDevice? = null
      override fun onReceive(
         context: Context,
         intent: Intent
      ) {
         val action = intent.action
         device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE)
         if (BluetoothDevice.ACTION_ACL_CONNECTED == action) {
            Toast.makeText(
               baseContext,
               "Device is now Connected",
               Toast.LENGTH_SHORT
            ).show()
         } else if (BluetoothDevice.ACTION_ACL_DISCONNECTED == action) {
            Toast.makeText(
               baseContext,
               "Device is disconnected",
               Toast.LENGTH_SHORT
            ).show()
         }
      }
   }
}

Step 4 − Add the following code to androidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="app.com.kotlipapp">
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>

Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click the Run  icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen −

Click here to download the project code.