Up Navigation: From Activity to Fragment: Android Studio

Question

The basic navigation of my app is a tab bar within one activity in which each tab is its own fragment. I am trying to get the back button to work to go back to the last tab it was on. I can get the back button to work/appear if the activities are going to the first tab by using this in the java class of the activity:

    getSupportActionBar().setDisplayHomeAsUpEnabled(true);

and this in the AndroidManifest.xml:

    <activity android:name=".CreateNewPost" android:parentActivityName=".MainActivity"></activity>

This works fine, however when I go to a new activity from a button within the other tabs, if I use this same method it goes to tab1. How do I tell it to go to a specific tab or the last active fragment? Any suggestions would help!

Answer 1

When you launch a new activity the old one either paused or stopped , as in either OnPause() or OnStop() method has been called. Then when you navigate back to a previous activity it is either started (OnStart()) or resuemd (OnResume()). And sometime the activity is destroyed and created again when navigating back to it using OnDestroy() and OnCreate() respectively.

The most guaranteed way that I can think of is to store the state of the first activity somewhere persistently and when the user navigates back to it check what has been stored and show that fragment. You can use SharedPreferences to store this kind of data, see the google developer documentation on that here. Or onSaveInstanceState(Bundle savedInstanceState) check out this SO question on saving activity state. Although from the answers it is clear that onSaveInstanceState should not work in your specific case, but you should look at it any way because it is useful in other cases like changing screen orientation for example.