How to remove old activities from backstack? (true way)

Issue

I'm new to Android development and here's my problem:
I have 2 activities: A and B. From A, I call B via startActivity(new Intent(A.this, B.class))
From B, I do some things and return to A the same way: startActivity(new Intent(B.this, A.class))
However, when on new-A I press "Back" button, first I see B class and then the old (unchanged version) of A class.

I've tried placing finish(); inside onPause() method. However, then my Activity crashes on orientation change.
How can I properly control activity backstack? Thanks in advance.

Solution

When you call startActivity without any additional flags, you will create a new instance of the Activity specified. This means that your back stack ends up looking like this:

A -> B -> A(2)

You have two options:

First option, you can add flags on the Intent that instructs it to reorder A to the front if it is already present in the back stack. Note that this will not close B; you have to call finish() in B afterward.

Intent intent = new Intent(B.this, A.class);
intent.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
startAcvitiy(intent);
finish();

Second option is to use startActivityForResult instead of startActivity in A and have Activity B pass a result back to A. I think this is much cleaner and it gives you a very easy way to react to what happened when B was finished (e.g. you can update your UI). See this guide from the Android developers site.

Answered By - Karakuri