How to prevent PendingIntent from creating a new activity in Android

Question

I'm making an APK file download screen and i show progress which is the percent of the file downloaded in the screen and also i have a notification to use a Foreground service because the file download must be downloaded from a service. During downloading, users can leave the app and can go back to my app through the notification. But the problem is, to achieve this logic, i use PendingIntent and when user click my app's notification, it recreates the app instead of going back to the previous screen earlier. I don't know why. please check my codes below.

File Download Fragment

 class FileDownloadFragment(private val uri: String) : DialogFragment() {

 ...

 override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
     super.onViewCreated(view, savedInstanceState)
     startDownloadService()
 }

 private fun startDownloadService() {
     val downloadService = AppUpdateAPKDownloadService()
     val startIntent = Intent(context, downloadService::class.java)
     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
         context.startForegroundService(startIntent)
     } else {
         context.startService(startIntent)
     }
 }

 ...

}

Foreground Service

  class AppUpdateAPKDownloadService: LifecycleService() {

  ...

  /** Dispatcher */
  private val ioDispatcher = Dispatchers.IO

  override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
      super.onStartCommand(intent, flags, startId)
      if (intent != null) {
          createNotificationChannel()
          val notification = getNotification()
          startForeground(NOTIFICATION_ID, notification)

          lifecycleScope.launch{
              downloadAPK(intent.getStringExtra(UPDATE_APK_URI).toString())
          }
      }

      return START_NOT_STICKY
  }

  private fun createNotificationChannel() {
      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
          val channel = NotificationChannel(
              CHANNEL_ID,
               CHANNEL_NAME,
              NotificationManager.IMPORTANCE_DEFAULT
          ).apply {
              enableVibration(true)
              enableLights(true)
          }
          val manager = this.getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
        manager.createNotificationChannel(channel)
      }
  }

  private fun getNotification(): Notification {
      val intent = Intent(applicationContext, SplashActivity::class.java)
      intent.flags = Intent.FLAG_ACTIVITY_CLEAR_TOP or Intent.FLAG_ACTIVITY_SINGLE_TOP
      val pendingIntent = TaskStackBuilder.create(applicationContext).run {
          addNextIntentWithParentStack(intent)
          getPendingIntent(APP_UPDATE_PENDING_INTENT_REQUEST_CODE, PendingIntent.FLAG_IMMUTABLE)
      }

      // val pendingIntent = PendingIntent.getActivity(
      //     applicationContext,
      //     APP_UPDATE_PENDING_INTENT_REQUEST_CODE,
      //     intent,
      //     PendingIntent.FLAG_IMMUTABLE
      //     )

      val notification = NotificationCompat.Builder(this, CHANNEL_ID).apply {
          setContentTitle("DownloadApp")
          setContentText("Downloading...")
          setSmallIcon(R.drawable.icon)
       setLargeIcon(BitmapFactory.decodeResource(this@AppUpdateAPKDownloadService.applicationContext.resources, R.mipmap.icon))
          priority = NotificationCompat.PRIORITY_HIGH
          setContentIntent(pendingIntent)
          setOngoing(true)
          setAutoCancel(true)
       }.build()

      val notificationManager = NotificationManagerCompat.from(this)
      notificationManager.notify(NOTIFICATION_ID, notification)

      return notification
  }

  private suspend fun downloadAPK(uri: String) = withContext(ioDispatcher) {
      kotlin.runCatching {
          URL(uri)
      }.onSuccess { url ->
          val connection: URLConnection = url.openConnection()
          connection.connect()

          val fileFullSize = connection.contentLength

          val directory = applicationContext.getExternalFilesDir(Environment.DIRECTORY_DOWNLOADS)
          directory?.let {
              if (!directory.exists()) directory.mkdirs()
          }

          val inputDataStream = DataInputStream(BufferedInputStream(url.openStream(), fileFullSize))
          val file = File(directory, "my_app.apk")
          val outputDataStream = DataOutputStream(BufferedOutputStream(FileOutputStream(file), fileFullSize))
          processDownload(
              inputStream = inputDataStream,
              outputStream = outputDataStream,
              fileFullSize = fileFullSize
          )

          val bundle = Bundle().apply {
              putInt(UPDATE_APK_RECEIVER_MODE, UPDATE_APK_DOWNLOAD_COMPLETE)
          }
          uiUpdateReceiver?.send(Activity.RESULT_OK, bundle)
      }.onFailure {
         
      }
  }

  private fun processDownload(
      inputStream: DataInputStream,
      outputStream: DataOutputStream,
      fileFullSize: Int
  ) {
      val data = ByteArray(fileFullSize)
      var downloadSize: Long = 0
      var count: Int

      while (inputStream.read(data).also { count = it } != -1) {
          downloadSize += count
          val percent = (downloadSize.toFloat() / fileFullSize) * 100
          Log.d("TEST", "writing...$percent% in Service")
          val bundle = Bundle().apply {
              putInt(UPDATE_APK_RECEIVER_MODE, UPDATE_APK_UI_UPDATE)
              putFloat(UPDATE_API_UI_PERCENT, percent)
          }
          uiUpdateReceiver?.send(Activity.RESULT_OK, bundle)
          outputStream.write(data, 0, count)
      }

      outputStream.flush()
      outputStream.close()
      inputStream.close()
  }

  ...
}

I also add android:launchMode="singleTop" to SplashActivity in AndroidManifest.xml but it's still not working...
What mistake did I make?

Answer 1

TaskStackBuilder will always recreate the activities. That's the way it is designed. You don't want to use it if you want to return to an existing task.

Instead of your code to create the PendingIntent, use this:

val intent = PackageManager.getLaunchIntentForPackage("your.package.name")
val pendingIntent = PendingIntent.getActivity(applicationContext,
            APP_UPDATE_PENDING_INTENT_REQUEST_CODE,
            intent,
            PendingIntent.FLAG_IMMUTABLE)

This will just cause your existing task to be brought to the foreground in whatever state it was in last. If your app is not running, this will launch your app as it would if you tapped the app icon on the HOME screen.

Answer 2

Okay, I solved this problem. it's 3 steps.

1. use PendingIntent.getActivity() instead of TaskStackBuilder.create(applicationContext).

2. use PendingIntent.FLAG_IMMUTABLE if you target Android M(API23) or above, or PendingIntent.FLAG_UPDATE_CURRENT if you target Android Lollipop(API21) or below.

3. add these flags Intent.FLAG_ACTIVITY_CLEAR_TOP or Intent.FLAG_ACTIVITY_SINGLE_TOP to the Intent.