Cleaning up activities in android

Question

I have four activities a,b,c,d. Activity a is the main activity which then calls b,c and d which then does some computation. I know I can prevent the activity from building up in my application by android:noHistory="true" attribute in those activites . But the issue is if I am in activity c,when I press the back button I want to go to b, but if d finishes I want b and c to be removed and only a to displayed. Is there any way to achieve this?

Have you already coded for the back button in each activity? — jcw, Nov 10 '12 at 08:22
Nope. I havent overridden the back button as I think its best to leave the function of the back button to the android system — user1667307, Nov 10 '12 at 08:29

score 1 · Accepted Answer · edited May 23 '17 at 12:04

1

Put this code in each of your activities, changing it slightly each time. That way you override the back button's normal function

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event)  {
        if (keyCode == KeyEvent.KEYCODE_BACK
                && event.getRepeatCount() == 0) {
            //start the desired activity
        }

        return super.onKeyDown(keyCode, event);
    }

Also, if you are only supporting android 2.0+ then you can use this

@Override
public void onBackPressed() {
    // start your desired activity here
    return;
}

Just put either of these in each of your activities, then start the correct activity

To close one specific activity, look at this page - How to clear specific activity from the stack history?

edited May 23 '17 at 12:04

Community

1
1

answered Nov 10 '12 at 08:31

jcw

5,132
7
45
54

The issue is not that I want to override the back button but to close n activities which have already piled up onto my stack. – user1667307 Nov 10 '12 at 08:40
Can you do this with `finish()` after you have started your new activity? – jcw Nov 10 '12 at 10:12
Nope. This will simply close all activites - If I am in activity c and I use finish() it will close b when I want to close activity b,c only if activity d has finished. I guess my best bet at this time is to use startActivityForResult() in my activities – user1667307 Nov 10 '12 at 10:18
http://stackoverflow.com/questions/5001882/how-to-clear-specific-activity-from-the-stack-history – jcw Nov 10 '12 at 10:24
Following the other question/answer he has linked, see mdelolmo's answer, not the accepted answer. It shows how to clear the stack. :) – IAmGroot Nov 10 '12 at 10:32
Yep. That kind of addresses what I want but the problem is there is no condition I can compare with to add the flag. I dont always want the activity stack to be cleared. Only if activity d has been executed. Any ideas? – user1667307 Nov 10 '12 at 10:37
Can you just put that particular price of code in activity d only? – jcw Nov 10 '12 at 11:03
Okay. I did it using startActivityForResult(). I guess that is the most efficient way of doing it. Thanks for the help – user1667307 Nov 10 '12 at 11:25

score 0 · Answer 2 · answered Nov 10 '12 at 10:28

Yes it can be acheived by making sure that you use a finish() function after every startActivity function. Except in the activity which you want to be displayed in the end.

So... Here is how it looks like

Code in A:

startActivity(Intent to start activity B);

Code in B:

startActivity(Intent to start activity C); 
Finish();

Code in C:

startActivity(Intent to start activity D); 
Finish();

This will ensure that whenever Activity D is completed, activity C will also be completed because of Finish. As this C is also completed, Finish() in activity B will close B. As there is no Finish() in Activity A, that activity will be displayed on the screen.

If you want to come to Activity A only after D is completed, you will have to use startActivityForResult and process the result and use IF to conditionally execute Finish statement in B & C.

Cleaning up activities in android

2 Answers2