Android: How do I avoid starting activity which is already in stack?

Question

Lets try to explain my question: I got an application and a service. The application is started with activity A. The service sends a broadcast that will let the application

Answer 1

Approaches android:launchMode="singleInstance" and just adding flags to the Intent do not work for me. What works is that:

In the code where activity gets started:

Intent intent = new Intent(activity, ActivityThatHasToBeStarted.class);
intent.setFlags(Intent.FLAG_ACTIVITY_BROUGHT_TO_FRONT);
startActivity(intent);

In the ActivityThatHasToBeStarted:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if ((getIntent().getFlags() & Intent.FLAG_ACTIVITY_BROUGHT_TO_FRONT) != 0) {
        finish();
        return;
    }
    // Code for this creation
}

Answer 2

I think you need to make your activity B singleInstance that if it's already create you don't want to create again, that is launch mode of the activity can be defined in manifest android:launchMode that defines how the activity will be instanciated.

in your case use android:launchMode="singleInstance"

Answer 3

If the activity will be on the top if already started, set the FLAG_ACTIVITY_SINGLE_TOP flag

intent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);
mContext.startActivity(intent);

Answer 4

You can use flag Intent.FLAG_ACTIVITY_NEW_TASK. If the activity is already running it will bring that to front instead of creating new activity.

If you add Intent.FLAG_ACTIVITY_CLEAR_TOP with this, then all the activities after this activity in the backstack will be cleared.

Answer 5

You may consider using android:launchMode="singleTop" instead of android:launchMode="singleInstance" Good article about the differences

Answer 6

If you don't need the second activity anymore, it is good practise to finish it, then you should do this on the second activity after the operation is ended:

startActivity(new Intent(this, FirstActivity.class).setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP));
finish();