Question

My appliaction features a menu with a logout button that allows you to log out from any Activity. This has been working fine. It used to log out to the app’s Welcome screen, but I recently changed it to log out to the device’s home screen. Now, when I log out and open the app, it force closes. On the second attempt to start the app, it will start correctly.

On the first attempt, it seems to try to load the Activity that was running when the user logged out, despite LogCat showing it starting the correct Intent:

08-13 17:14:18.983: INFO/ActivityManager(59): Starting activity: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=uk.ac.ic.doc.vmw10.wherewolf/.activities.Welcome }
08-13 17:14:19.053: VERBOSE/WWA(8611): setting up
08-13 17:14:19.064: DEBUG/AndroidRuntime(8611): Shutting down VM
08-13 17:14:19.064: WARN/dalvikvm(8611): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
08-13 17:14:19.083: ERROR/AndroidRuntime(8611): FATAL EXCEPTION: main
08-13 17:14:19.083: ERROR/AndroidRuntime(8611): java.lang.RuntimeException: Unable to resume activity {uk.ac.ic.doc.vmw10.wherewolf/uk.ac.ic.doc.vmw10.wherewolf.activities.Tabs}: java.lang.NullPointerException

Immediately after it starts the correct Intent, a verbose message is output from the wrong activity, and then the app crashes due to a NullPointerException. Why is it not starting the Welcome activity, as the Intent claims it is?

Here’s the logout function:

public void logout() {
    SharedPreferences.Editor prefEditor = preferences.edit();
    prefEditor.remove(PASSWORD);
    prefEditor.remove(FIRST_NAME);
    prefEditor.remove(LAST_NAME);
    prefEditor.remove(EMAIL_ADDRESS);
    prefEditor.remove(DATE);    
    prefEditor.remove(PICTURE); 
    prefEditor.remove(TOKEN);   
    prefEditor.commit();

    final Intent intent = new Intent(Intent.ACTION_MAIN);
    intent.addCategory(Intent.CATEGORY_HOME);
    intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    syncTask.cancel(true);
    dbHelper.close();
    dbHelper=null;
    firstRun = true;
    startActivity(intent); 
}

Edit: Here’s the onCreate method for the Welcome Activity:

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
    Log.v(TAG, "preferences: "+preferences.getAll());
    if(preferences.contains(WhereWolfActivity.EMAIL_ADDRESS)) {
        Log.v(TAG, "user preferences saved from previous session: "+preferences.getAll().toString());
        intent = new Intent(getApplicationContext(), Tabs.class);
        startActivity(intent);
        finish();
    }
    else if(preferences.contains(WhereWolfActivity.USER_ID) &! preferences.contains(WhereWolfActivity.EMAIL_ADDRESS)) {
        Log.v(TAG, "known user returning to log in");
        intent = new Intent(getApplicationContext(), Login.class);
        startActivity(intent);
        finish();
    }
    else {
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.welcome);
    }  
}

Edit:

Not only is it starting the wrong Activity, it is not calling the onCreate method of that Activity, but it does call onStart. Ths suggests that it is trying to pick up where it left off, even though that’s not what I want it to do! How can I persuade it not to do this?

Edit:

As all my ‘logged in’ Activity’s have a superclass they inherit from, I added a bit to that superclass’s onStart() method that would check if the user was logged in, and if not it would start the Welcome Activity:

public void onStart () {
    super.onStart();
    if(!preferences.contains(EMAIL_ADDRESS)) {
        Log.v(TAG, "not logged in");
        Intent intent = new Intent(getApplicationContext(), Welcome.class);
        intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        startActivity(intent);
        finish();
    }

This hasn’t worked. Here’s the LogCat output:

08-13 20:41:10.223: INFO/ActivityManager(59): Starting activity: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10200000 cmp=uk.ac.ic.doc.vmw10.wherewolf/.activities.Welcome }
08-13 20:41:10.254: VERBOSE/WWA(2171): not logged in
08-13 20:41:10.263: INFO/ActivityManager(59): Starting activity: Intent { flg=0x4000000 cmp=uk.ac.ic.doc.vmw10.wherewolf/.activities.Welcome }
08-13 20:41:10.273: VERBOSE/WWA(2171): setting up
08-13 20:41:10.320: DEBUG/AndroidRuntime(2171): Shutting down VM
08-13 20:41:10.320: WARN/dalvikvm(2171): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
08-13 20:41:10.343: ERROR/AndroidRuntime(2171): FATAL EXCEPTION: main
08-13 20:41:10.343: ERROR/AndroidRuntime(2171): java.lang.RuntimeException: Unable to resume activity {uk.ac.ic.doc.vmw10.wherewolf/uk.ac.ic.doc.vmw10.wherewolf.activities.Tabs}: java.lang.NullPointerException

The superclass has the tag WWA. As you can see, it says ‘not logged in’, then starts the Welcome Activity, and then carries on anyway. Any ideas?

Answer 1

I solved the problem by adding this to the onPause() method of my superclass:

if(!preferences.contains(EMAIL_ADDRESS)) { // this means the user has logged out
    finish();
}

Now, when the user logs out, all Activity’s are finished properly. I also changed it back to logging out to the log in screen rather than logging out to the device’s home screen after reading this post: Is quitting an application frowned upon?