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

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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);

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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