Building a synthetic task stack of multiple activities in Android

My learning around creating a synthetic task stack of multiple activities with TaskStackBuilder or startActivities

The scenario we wanted to implement in Android was as follows:

1. Launch activity A - SplashScreen

2. Activity B should be launched immediately- SecondActivity

3. On back of Activity B, we should launch Activity C. - ParentActivity

To implement this, we used TaskStackBuilder

In onCreateof Activity A (Splash Screen), we implemented:

 Intent secondActivity = new Intent(this, SecondActivity.class);
 TaskStackBuilder stackBuilder = TaskStackBuilder
 .create(secondActivity);
  stackBuilder.addNextIntentWithParentStack(secondActivity.class);

 PendingIntent pendingIntent = stackBuilder
 .getPendingIntent( 0, PendingIntent.FLAG_UPDATE_CURRENT);
 pendingIntent.send(this, 0,  secondActivity);

Instead of using .addNextIntentWithParentStack you can also use:

stackBuilder.addParentStack(secondActivity.class);
stackBuilder.addNextIntent(secondActivity);

In the manifest we have to define the parent:

If you are using below API 16:

<activity android:name =".SecondActivity"> 
  <meta-data
    android:name="android.support.PARENT_ACTIVITY"
    android:value=".ThirdActivity"/>
</activity>

API 16+

<activity android:name=".SecondActivity"
    android:parentActivityName=".ThirdActivity"
.../>

But we faced a issue - Two tasks were getting created for the app when the above scenario was executed.

Looking at the internals, we saw the TaskStackBuilder.createreturns a new TaskStackBuilder for launching a fresh task stack consisting of a series of activities. Internally, Intent.FLAG_ACTIVITY_NEW_TASK is set. Then we realized that our activity C (ParentActivity) has a particular taskAffinity; different from the default one.

By default all activities have the same taskAffinity and therefore even though we set Intent.FLAG_ACTIVITY_NEW_TASK, the new Activity will still be started in the same task. But, if the new Activity has a different taskAffinity, the new Activity will be started in a new task.

Solution: We added the particular taskAffinity to Activity A and B. **But a better approach, we heard is use startActivities.**

On digging further, we understood it can be used to create a synthetic back stack, when starting a new Task. You want to have a ready-made back stack, so that the back key navigates hierarchically inside this task.

startActivities(intents) is available from API 11

So we created intents for Activity B and C and this worked as a breeze Intents[] intents = {parentActivity, secondActivity} startActivities(intents);

UPDATE: We found a bug in our app while using startActivities

As stated above we had to launch ActivityA(Splash Screen) and then launch ActivityB. While launching the Splash Screen, we put the application in the background, the app crashes. What we understood is, as we are starting ActivityB from the non UI thread, it led to the crash. Another related raised issue with startActivities.

Therefore, we reverted to using TaskStackBuilder.

References:

http://developer.android.com/reference/android/support/v4/content/ContextCompat.html#startActivities%28android.content.Context,%20android.content.Intent%5B%5D%29 http://stackoverflow.com/questions/21374610/use-of-android-taskaffinity

We learned quite some new things while solving the above mentioned issue and therefore thought of sharing our learnings.

Hope you find this post helpful. Do you all know of any other better approach. Let us know.