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

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