Developing an Android App to Auto-Answer Incoming Calls Using Kotlin

In this blog post, we will explore how to develop an Android app using Kotlin that targets Android versions 10 to 14. The primary feature of this app is to auto-answer incoming calls. Please note that due to restrictions in Android, this feature requires the app to be set as the default dialer app.

Step-by-Step Guide

1. Set Up Your Project

Create a new Android Project:
- Open Android Studio.
- Start a new Android Studio project.
- Choose an empty activity.
- Name your application (e.g., "AutoAnswerApp").
- Select Kotlin as the language.
- Set the minimum API level to 29 (Android 10).

Add Necessary Permissions:

Open AndroidManifest.xml and add the required permissions:

  <uses-permission android:name="android.permission.READ_PHONE_STATE" />
  <uses-permission android:name="android.permission.ANSWER_PHONE_CALLS" />

2. Implement the Auto-Answer Feature

Create a BroadcastReceiver to Listen for Incoming Calls:

Create a new Kotlin file CallReceiver.kt and define a BroadcastReceiver to handle incoming call events.

  import android.content.BroadcastReceiver
  import android.content.Context
  import android.content.Intent
  import android.os.Build
  import android.telecom.TelecomManager
  import android.telephony.TelephonyManager

  class CallReceiver : BroadcastReceiver() {
      override fun onReceive(context: Context, intent: Intent) {
          if (intent.action == TelephonyManager.ACTION_PHONE_STATE_CHANGED) {
              val state = intent.getStringExtra(TelephonyManager.EXTRA_STATE)
              if (state == TelephonyManager.EXTRA_STATE_RINGING) {
                  answerCall(context)
              }
          }
      }

      private fun answerCall(context: Context) {
          if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
              val telecomManager = context.getSystemService(Context.TELECOM_SERVICE) as TelecomManager
              telecomManager.acceptRingingCall()
          }
      }
  }

Register the BroadcastReceiver in the Manifest:

Update your AndroidManifest.xml to register the CallReceiver:

  <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">

      <receiver android:name=".CallReceiver">
          <intent-filter>
              <action android:name="android.intent.action.PHONE_STATE" />
          </intent-filter>
      </receiver>

      <activity android:name=".MainActivity">
          <intent-filter>
              <action android:name="android.intent.action.MAIN" />
              <category android:name="android.intent.category.LAUNCHER" />
          </intent-filter>
      </activity>
  </application>

Request Runtime Permissions:

Android 6.0 (API level 23) and higher requires apps to request permissions at runtime.

In your MainActivity.kt, add the necessary code to request the required permissions at runtime.

  import android.Manifest
  import android.content.pm.PackageManager
  import android.os.Bundle
  import androidx.appcompat.app.AppCompatActivity
  import androidx.core.app.ActivityCompat
  import androidx.core.content.ContextCompat

  class MainActivity : AppCompatActivity() {

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

          // Check and request permissions
          checkAndRequestPermissions()
      }

      private fun checkAndRequestPermissions() {
          val permissions = arrayOf(
              Manifest.permission.READ_PHONE_STATE,
              Manifest.permission.ANSWER_PHONE_CALLS
          )

          val permissionsToRequest = permissions.filter {
              ContextCompat.checkSelfPermission(this, it) != PackageManager.PERMISSION_GRANTED
          }

          if (permissionsToRequest.isNotEmpty()) {
              ActivityCompat.requestPermissions(this, permissionsToRequest.toTypedArray(), 0)
          }
      }

      override fun onRequestPermissionsResult(
          requestCode: Int,
          permissions: Array<out String>,
          grantResults: IntArray
      ) {
          super.onRequestPermissionsResult(requestCode, permissions, grantResults)
          for (result in grantResults) {
              if (result != PackageManager.PERMISSION_GRANTED) {
                  // Handle the case where the permission is not granted
              }
          }
      }
  }

Note on API Level Restrictions

Starting from Android 10 (API level 29), the ability to auto-answer calls is restricted to system apps. Regular apps do not have the permissions to perform this action unless they are set as the default dialer app. This means you might need to set your app as the default dialer to achieve auto-answer functionality.

Set App as Default Dialer

Declare the Dialer Activity:

In your AndroidManifest.xml, declare an activity that handles the Intent.ACTION_DIAL and Intent.ACTION_CALL intents.

  <activity
      android:name=".DialerActivity"
      android:theme="@style/AppTheme.NoActionBar">
      <intent-filter>
          <action android:name="android.intent.action.DIAL" />
          <action android:name="android.intent.action.CALL" />
          <category android:name="android.intent.category.DEFAULT" />
      </intent-filter>
  </activity>

Create DialerActivity Class:

Create a new Kotlin file named DialerActivity.kt and define the activity.

  import android.os.Bundle
  import androidx.appcompat.app.AppCompatActivity

  class DialerActivity : AppCompatActivity() {
      override fun onCreate(savedInstanceState: Bundle?) {
          super.onCreate(savedInstanceState)
          setContentView(R.layout.activity_dialer)
      }
  }

Add Layout for DialerActivity:

Create a new layout file named activity_dialer.xml in res/layout/.

  <?xml version="1.0" encoding="utf-8"?>
  <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
      android:layout_width="match_parent"
      android:layout_height="match_parent">

      <TextView
          android:id="@+id/dialerText"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_centerInParent="true"
          android:text="Dialer Activity"
          android:textSize="24sp"/>
  </RelativeLayout>

Prompt User to Set Default Dialer:

In your MainActivity.kt, add logic to prompt the user to set your app as the default dialer.

  import android.content.Intent
  import android.os.Bundle
  import android.telecom.TelecomManager
  import androidx.appcompat.app.AppCompatActivity

  class MainActivity : AppCompatActivity() {

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

          // Check and request permissions
          checkAndRequestPermissions()

          // Prompt to set as default dialer
          setDefaultDialer()
      }

      private fun setDefaultDialer() {
          val telecomManager = getSystemService(TELECOM_SERVICE) as TelecomManager
          if (telecomManager.defaultDialerPackage != packageName) {
              val intent = Intent(TelecomManager.ACTION_CHANGE_DEFAULT_DIALER)
              intent.putExtra(TelecomManager.EXTRA_CHANGE_DEFAULT_DIALER_PACKAGE_NAME, packageName)
              startActivityForResult(intent, 1)
          }
      }

      override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
          super.onActivityResult(requestCode, resultCode, data)
          if (requestCode == 1) {
              if (resultCode == RESULT_OK) {
                  // Your app is now the default dialer
              } else {
                  // The user declined to set your app as the default dialer
              }
          }
      }
  }

Conclusion

By following these steps, you can create an Android app that targets versions 10 to 14 and can auto-answer incoming calls. Note that due to restrictions in Android, this will only work if your app is set as the default dialer. Handling such permissions and system interactions requires careful consideration of user privacy and compliance with Google Play policies.