Know when to show a passcode lock

Question

I am developing an application that needs to display a passcode screen whenever a user leaves the app and comes back (be it through a screen lock, or going back to the home screen through the back or home button). I had it working using the following:

The starting activity would call for the passcode check on startup, and each activity added the following functionality to their onPause method:

@Override
public void onPause() {
    super.onPause();

    if (!isFinishing()) {
    new PasscodeCheckTask(this.getApplicationContext(),this).execute();
    }
}

The PassocdeCheckTask looks like the following. It checks to see if the screen is off or the app is no longer in the background

public class PasscodeCheckTask extends AsyncTask<Void, Void, Boolean> {

    public static final int CHECK_PASSCODE = 0;

    private Context mActivityApplicationContext;
    private Context mActivityContext;

    public PasscodeCheckTask(Context applicationContext, Context activityContext){
        mActivityApplicationContext = applicationContext;
        mActivityContext = activityContext;
    }

    @Override
    protected Boolean doInBackground(Void... params) {
        Boolean result = false;

        if (!((PowerManager)mActivityApplicationContext.getSystemService(android.content.Context.POWER_SERVICE)).isScreenOn() ||
            !isAppOnForeground(mActivityApplicationContext)) {
            result = true;
        }
        return result;
    }

    @Override
    protected void onPostExecute(Boolean result) {
        if (result) {
            // Start passcode activity to check for passcode
            /* CODE HERE */
            ((Activity)mActivityContext).startActivityForResult(intent, CHECK_PASSCODE);
        }
    }

    protected boolean isAppOnForeground(final Context context) {
        List<RunningAppProcessInfo> appProcesses = ((ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE)).getRunningAppProcesses();

        if (appProcesses == null) {
            return false;
        }

        final String packageName = context.getPackageName();
        for (RunningAppProcessInfo appProcess : appProcesses) {
            if ((appProcess.importance == RunningAppProcessInfo.IMPORTANCE_FOREGROUND) && 
                 appProcess.processName.equals(packageName)) {
                return true;
            }
        }
        return false;
    }
}

The Passcode activity would finish when done, and the calling activity would moveTaskToBackground(true) if the passcode didn't pass. This system worked beautifully until I tried it on an HTC Evo with mikg ROM. For some reason, the appProcess.importance never showed up as IMPORTANCE_FOREGROUND. It was always IMPORTANCE_BACKGROUND. Thus, the passcode would ALWAYS be brought up, even though the app never went into the background.

I tried DropBox on that phone (which has a passcode lock as well), and it worked beautifully. I can't seem to find a different way to know when an app has gone to the background, or if it is being brought back from the background. Any ideas on how to make this work?

Answer 1

In onStop() of each activity, update a static data member with the time you left the activity. In onStart() of each activity, check that time, and if it exceeds some timeout threshold, display your authentication activity. Allow the user to set the timeout value, so that if they don't want to be bothered every few seconds, they can control that.

Answer 2

I liked the time based approach, I've been struggling for a while getting this to work in a nice way. The time based approach works well. I made a class for easier usage.

public class PinCodeCheck {

    private static long INIT_TIME           = 0;
    private static PinCodeCheck ref         = null;
    private static SharedPreferences values = null;

    private PinCodeCheck(Context context){
        values = context.getSharedPreferences("com.example.xxx", 0); //use your preferences file name key!
    }//end constructor

    public static synchronized PinCodeCheck getInstance(Context context) {
        if (ref == null){
            ref = new PinCodeCheck(context);
        } 
        return ref;
    }//end method 

    public void init(){
        PinCodeCheck.INIT_TIME = System.currentTimeMillis();    
    }//end method   

    public void forceLock(){
        PinCodeCheck.INIT_TIME = 0;     
    }//end method   

    public boolean isLocked(){
        long currentTime    = System.currentTimeMillis();
        long threshold      = values.getLong(Keys.PASSWORD_PROTECT_TIMEOUT, 30000); // check here, might change in between calls
        if (currentTime - PinCodeCheck.INIT_TIME > threshold){
            return true;
        }
        return false;       
    }//end method   
}//end class

---

USAGE

private static PinCodeCheck check   = PinCodeCheck.getInstance(context);

@Override
public void onResume() {
    super.onResume();  

    if (check.isLocked()) { 
        showDialog();               
    }
}//end method 

@Override
public void onPause() {          
    super.onPause();

    check.init();
}//end method