Android: Clear Activity Stack

Question

I'm having several activities in my application. and flow is very complicated. When I click the Logout application naviagates to login Screen and from there user can exit by cancel buton (calling system.exit(0) )

when I exit or back button, system invokes an activity from stack :( how can I clear all the activities in the stack when i reach Login screen? calling finish() is not practical as there are so many activities and some activities should no be closed when they are active such as native camera invoking activity.

validateuser logoutuser = new validateuser();
logoutuser.logOut();
Intent loginscreen = new Intent(homepage.this, Login2.class);
(homepage.this).finish();
loginscreen.setFlags( Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_NO_HISTORY);
startActivity(loginscreen);

Answer 1

This decision works fine:

intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);

But new activity launch long and you see white screen some time. If this is critical then use this workaround:

public class BaseActivity extends AppCompatActivity {

    private static final String ACTION_FINISH = "action_finish";

    private BroadcastReceiver finisBroadcastReceiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        registerReceiver(finisBroadcastReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                finish();
            }
        }, new IntentFilter(ACTION_FINISH));
    }

    public void clearBackStack() {
        sendBroadcast(new Intent(ACTION_FINISH));
    }

    @Override
    protected void onDestroy() {
        unregisterReceiver(finisBroadcastReceiver);
        super.onDestroy();
    }
}

How use it:

public class ActivityA extends BaseActivity {

    // Click any button
    public void startActivityB() {
        startActivity(new Intent(this, ActivityB.class));
        clearBackStack();
    }
}

Disadvantage: all activities that must be closed on the stack must extends BaseActivity

Answer 2

When you call startActivity on the last activity you could always use

Intent.FLAG_ACTIVITY_CLEAR_TOP

as a flag on that intent.

Read more about the flag here.

Answer 3

Most of you are wrong. If you want to close existing activity stack regardless of what's in there and create new root, correct set of flags is the following:

intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);

From the doc:

public static final int FLAG_ACTIVITY_CLEAR_TASK
Added in API level 11

If set in an Intent passed to Context.startActivity(), this flag will cause any existing task that would be associated with the activity to be cleared before the activity is started. That is, the activity becomes the new root of an otherwise empty task, and any old activities are finished. This can only be used in conjunction with FLAG_ACTIVITY_NEW_TASK.

Answer 4

Here is a simple helper method for starting a new activity as the new top activity which works from API level 4 up until the current version 17:

static void startNewMainActivity(Activity currentActivity, Class<? extends Activity> newTopActivityClass) {
    Intent intent = new Intent(currentActivity, newTopActivityClass);
    intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)
        intent.addFlags(0x8000); // equal to Intent.FLAG_ACTIVITY_CLEAR_TASK which is only available from API level 11
    currentActivity.startActivity(intent);
}

call it like this from your current activity:

startNewMainActivity(this, MainActivity.class);

Answer 5

In my case, LoginActivity was closed as well. As a result,

Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_CLEAR_TASK

did not help.

However, setting

Intent.FLAG_ACTIVITY_NEW_TASK

helped me.

Answer 6

For Xamarin Developers, you can use:

intent.SetFlags(ActivityFlags.NewTask | ActivityFlags.ClearTask);