As of Android version 10 (SDK version 29), the other answers will no longer work if the app is running this in the background, for example in a BroadcastReceiver
.
In order to make it work on Android 10 and onwards, you should use a full-screen intent if you really need to start an activity from the background [source]:
Android 10 (API level 29) and higher place restrictions on when apps can start activities when the app is running in the background. These restrictions help minimize interruptions for the user and keep the user more in control of what's shown on their screen.
In nearly all cases, apps that are in the background should display time-sensitive notifications to provide urgent information to the user instead of directly starting an activity. Examples of when to use such notifications include handling an incoming phone call or an active alarm clock.
This can be achieved as follows [source]:
val fullScreenIntent = Intent(this, CallActivity::class.java)
val fullScreenPendingIntent = PendingIntent.getActivity(this, 0,
fullScreenIntent, PendingIntent.FLAG_UPDATE_CURRENT)
val notificationBuilder =
NotificationCompat.Builder(this, CHANNEL_ID)
.setSmallIcon(R.drawable.notification_icon)
.setContentTitle("Incoming call")
.setContentText("(919) 555-1234")
.setPriority(NotificationCompat.PRIORITY_HIGH)
.setCategory(NotificationCompat.CATEGORY_CALL)
// Use a full-screen intent only for the highest-priority alerts where you
// have an associated activity that you would like to launch after the user
// interacts with the notification. Also, if your app targets Android 10
// or higher, you need to request the USE_FULL_SCREEN_INTENT permission in
// order for the platform to invoke this notification.
.setFullScreenIntent(fullScreenPendingIntent, true)
val incomingCallNotification = notificationBuilder.build()
Portions of this answer are reproduced from work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.