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 start Activity B Now the user starts activity C.

Now the service wants to start activity B again. But how do I let him know that the activity is still on the stack, or is there an intent flag for this?

How do I avoid that it will launch activity B because its already in the stack?

What is D exactly? Is it code you are writing? If so, the answer is simple, **don't** call `StartActivity(B)`. — David Schwartz, Mar 07 '12 at 08:58

MKJParekh · Accepted Answer · 2012-10-07T06:53:51.513

82

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"

edited Oct 07 '12 at 06:53

answered Mar 07 '12 at 09:12

MKJParekh

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But if I set the launchMode to singleInstance I will not get the onActivityResult callbacks rightly. – DevAndroid Sep 04 '15 at 12:22
Work like a charm! – SerSánGal Aug 24 '16 at 08:18

score 30 · Answer 2 · answered Mar 07 '12 at 09:10

30

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.

answered Mar 07 '12 at 09:10

Sadeshkumar Periyasamy

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This is exaclty what I don't want to happen. If there is already a activity over the started activity. It shouldnt be overridden. – Ion Aalbers Mar 07 '12 at 09:11
1

This will not override the activity. It will bring front the already started activity only. – Sadeshkumar Periyasamy Mar 07 '12 at 09:23
5

Intent.FLAG_ACTIVITY_NEW_TASK is not work for me.. this always start new activity .. please help me out – Vaishali Sutariya Aug 08 '14 at 06:08
@VaishaliSutariya try FLAG_ACTIVITY_CLEAR_TOP – guisantogui Mar 31 '16 at 20:16
1

Starting activity with this intents makes the onCreate method to be called again. – htafoya Oct 13 '17 at 00:10

score 11 · Answer 3 · answered Sep 26 '14 at 06:36

11

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);

answered Sep 26 '14 at 06:36

Pellet

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This is escpecially usefull when using a sidebar/drawer and you don't wanta to open an activity twice when already in front. – dermatthias Dec 17 '15 at 15:54
I am starting an activity from a servi using Intent.FLAG_ACTIVITY_SINGLE_TOP, the activity does not start and I get this error: android.util.AndroidRuntimeException: Calling startActivity() from outside of an Activity context requires the FLAG_ACTIVITY_NEW_TASK flag. Is this really what you want? – yeahman Mar 10 '16 at 18:36
1

Exactly what I was looking for :) – cantona_7 Aug 22 '19 at 07:52

score 7 · Answer 4 · edited Apr 19 '16 at 20:34

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
}

score 4 · Answer 5 · answered Jan 14 '18 at 11:07

4

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

answered Jan 14 '18 at 11:07

Gal Rom

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score 2 · Answer 6 · answered Jun 09 '15 at 05:51

2

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();

answered Jun 09 '15 at 05:51

Alex

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This is good, but returns null on the TextViews of the first page activity. – Bay Sep 12 '19 at 21:07

score -1 · Answer 7 · answered Oct 19 '17 at 09:19

I would suggest you use Intent.FLAG_ACTIVITY_CLEAR_TOP as it will remove all activities which start on top of your targeted activity.

eg :

Intent intent = new Intent(sourceActivity, Target activity);

intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

startActivity(intent)

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

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