Dealing with phone's back button: Back button on home activity always to cause app exit

Let's say I have 4 activities in my app:

A (main activity)

B

C

D

I would like that pressing back in Activity A always produce application exit. In my case if activity flow goes like this A > B > C > A, then if I push back b开发者_JAVA技巧utton, I will go to activity C. I want, at that moment, my app to exit.

I assume, app should somehow delete activity history when main activity is active.

How is this to be done?

Thanks

When you launch your home activity do so with the clear top flag set. This causes the back stack to be cleared.

Intent intent = new Intent(this, HomeActivity.class);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);

If you want the above behaviour then use the FLAG_ACTIVITY_CLEAR_TOP to launch A. This will clear the all the activities above A