Activity in launchMode singleTask gets destroyed when started via TaskStackBuilder

Question

I have an activity A , declared in Manifest with android:launchMode="singleTask" and another activity B that has no further attributes.

As far as I know, if there is already some task running activity A, instead of creating a new instance, the current task is brought to front, if I attempt to start activity A.

Now, I want to use the TaskStackBuilder to make a call which includes both activities.

Let's suppose I am on a Fragment within Activity A and call:

                TaskStackBuilder.create(context)
                    .addNextIntent(new Intent(context, A.class))
                    .addNextIntent(new Intent(context, B.class))
                    .startActivities();

I assume the current stack to become: A > B with A getting a call to onNewIntent and B with a new instance. Furthermore I expect Activity A to hold it's state.

But what happens is: I do not get a call to onNewIntent , but to onDestroy for Activity A . And if I go back from my newly created Activity B , onCreate is called for a new instance of Activity A . (They are not equal!).

Can anybody explain to me, why my Activity A is thrown away instead of doing nothing to it, but adding B to the stack? It is a shame, that I can't get my head around this problem by myself, but I can't see the obstacle here.

Edit/Ps: The context which I use for the StackBuilder can either be a views context or a Service context.

Answer 1

So, as nobody answered so far, I dived into the code from android in the meanwhile and discovered that the StackBuilder itself is the issue .

In detail..this part of code, which is present in the methods startActivities() and also in getPendingIntent() , causes my Activity A to get destroyed:

    public PendingIntent getPendingIntent(int requestCode, int flags, Bundle options) {
        if (mIntents.isEmpty()) {
            throw new IllegalStateException(
                    "No intents added to TaskStackBuilder; cannot getPendingIntent");
        }

        Intent[] intents = mIntents.toArray(new Intent[mIntents.size()]);
        intents[0] = new Intent(intents[0]).addFlags(Intent.FLAG_ACTIVITY_NEW_TASK |
            IntentCompat.FLAG_ACTIVITY_CLEAR_TASK |
            IntentCompat.FLAG_ACTIVITY_TASK_ON_HOME);
        // Appropriate flags will be added by the call below.
        return IMPL.getPendingIntent(mSourceContext, intents, requestCode, flags, options);
    }

It is this part:

Intent[] intents = mIntents.toArray(new Intent[mIntents.size()]);
    intents[0] = new Intent(intents[0]).addFlags(Intent.FLAG_ACTIVITY_NEW_TASK |
            IntentCompat.FLAG_ACTIVITY_CLEAR_TASK |
            IntentCompat.FLAG_ACTIVITY_TASK_ON_HOME);

My Activity A was in an existing Task. Although it has the launchMode = "singleTask" and should get reordered to front normally, the FLAG_ACTIVITY_CLEAR_TASK is set to my first activity (which is A ) and causes the existing task that would be associated with the A to be cleared before the activity is started.

That said, I won't use the StackBuilder in my special case now. I see several approaches to this: either use an empty Activity before my first target Activity or building the stack myself inside of my Activity A 's onCreate / onNewIntent , by providing a Bundle with a List of parcelables (intents) to start.