handler.postDelayed not working correctly

Question

I have a simple stopwatch code piece. Thread is running in custom class, it connects to the main activity via Interface

public class MainActivity extends AppCompatActivity implements MainActivityInteractionInterface{
public static boolean isRunning = false;
Stopwatch stopWatch;
private TextView textViewMilliSeconds;
private TextView textViewSeconds;
@Override
protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 textViewMilliSeconds = findViewById(R.id.textViewStopwatchMilliseconds);
 textViewSeconds = findViewById(R.id.textViewStopwatchSeconds);
 stopWatch = new Stopwatch(this, getApplicationContext());
 stopWatch.runThread();
}
@Override
public void updateUI() {
 String time = String.format(Locale.getDefault(), "%03d", stopWatch.getMilliseconds());
 textViewMilliSeconds.setText(time);
 String timeSeconds = String.format(Locale.getDefault(), "%02d", stopWatch.getSeconds());
 textViewSeconds.setText(timeSeconds);
}
public void startTimer(View view) {
 isRunning = !isRunning;
}

---

public class Stopwatch {
private int milliseconds = 0;
private int seconds = 0;
public int getMilliseconds() {
 return milliseconds;
}
public int getSeconds() {
 return seconds;
}
private MainActivityInteractionInterface interactionInterface;
private Context applicationContext;
public Stopwatch(MainActivityInteractionInterface interactionInterface, Context applicationContext){
 this.interactionInterface = interactionInterface;
 this.applicationContext = applicationContext;
}
public void runThread(){
 final Handler handler = new Handler();
 handler.post(new Runnable(){
 @Override
 public void run(){
 if(isRunning) {
 milliseconds++;
 if (milliseconds == 1000) {
 milliseconds = 0;
 seconds++;
 if(seconds == 60){
 seconds = 0;
 }
 }
 }
 interactionInterface.updateUI();
 handler.postDelayed(this, 1);
 }
 });
}

handler should update every 1 millisec, when there is 1000 milliseconds, 1 second passes by If I set handler.postDelayed delay anything below 15 reaching 1000 milliseconds would take exactly 18 seconds, why?

Answer 1

I don't know why it would take up to 18seconds, but I can tell you this: Android refresh the UI every 16msec (to have a rate of 60fps), so setting the handler to updateUI in a lesser time would make no sense and maybe also interfier with it.

In my humble opinion, make it to update in 20msec and change the counter values according, like this:

handler.post(new Runnable(){
 @Override
 public void run(){
 if(isRunning) {
 milliseconds++;
 if (milliseconds == 50) {
 milliseconds = 0;
 seconds++;
 if(seconds == 60){
 seconds = 0;
 }
 }
 }
 interactionInterface.updateUI();
 handler.postDelayed(this, 20);
 }
});

Answer 2

Look at the second argument of handler.postDelayed(this, 1);

Change it according to the way you increment your milliseconds.