[android] Android: Clear Activity Stack

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

when I exit or back button, the 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);

For Xamarin Developers, you can use:

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

Using Kotlin:

You can set the flag directly using setter method. In Kotlin or is the replacement for the Java bitwise or |.

intent.flags = FLAG_ACTIVITY_NEW_TASK or FLAG_ACTIVITY_CLEAR_TASK

If you plan to use this regularly, create an Intent extension function

fun Intent.clearStack() {
    flags = Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TASK
}

You can then directly call this function before starting the intent

intent.clearStack()

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.

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

Intent intent = new Intent(LoginActivity.this,MainActivity.class); intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK); startActivity(intent); finish();

Clear Activity Backstate by below code:

Intent intent = new Intent(Your_Current_Activity.this, Your_Destination_Activity.class);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK |Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);

Done

I noted that you asked for a solution that does not rely on finish(), but I wonder if this may help nonetheless.

I tracked whether an exit flag is raised with a static class variable, which survives the entire app lifespan. In each relevant activity's onResume(), use

@Override
public void onResume() {
    super.onResume();
    if (ExitHelper.isExitFlagRaised) {
        this.finish();
    }
}

The ExitHelper class

public class ExitHelper {
    public static boolean isExitFlagRaised = false;
}

Let's say in mainActivity, a user presses a button to exit - you can set ExitHelper.isExitFlagRaised = true; and then finish(). Thereafter, other relevant activities that are resumed automatically will be finished as well.

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.

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);

Intent intent = new Intent(LoginActivity.this, Home.class);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);  //It is use to finish current activity
startActivity(intent);
this.finish();