android CountDownTimer – additional milliseconds delay between ticks

Rewrite

As you said, you also noticed that the next time in onTick() is calculated from the time the previous onTick() ran, which introduces a tiny error on every tick. I changed the CountDownTimer source code to call each onTick() at the specified intervals from the start time.

I build this upon the CountDownTimer framework, so cut & paste the source code into your project and give the class a unique name. (I called mine MoreAccurateTimer.) Now make a few changes:

1. Add a new class variable:

   private long mNextTime;
   

2. Change start():

   public synchronized final MoreAccurateTimer start() {
       if (mMillisInFuture <= 0) {
           onFinish();
           return this;
       }
   
       mNextTime = SystemClock.uptimeMillis();
       mStopTimeInFuture = mNextTime + mMillisInFuture;
   
       mNextTime += mCountdownInterval;
       mHandler.sendMessageAtTime(mHandler.obtainMessage(MSG), mNextTime);
       return this;
   }
   

3. Change the Handler’s handlerMessage():

   @Override
   public void handleMessage(Message msg) {
       synchronized (MoreAccurateTimer.this) {
           final long millisLeft = mStopTimeInFuture - SystemClock.uptimeMillis();
   
           if (millisLeft <= 0) {
               onFinish();
           } else {
               onTick(millisLeft);
   
               // Calculate next tick by adding the countdown interval from the original start time
               // If user's onTick() took too long, skip the intervals that were already missed
               long currentTime = SystemClock.uptimeMillis();
               do {
                   mNextTime += mCountdownInterval;
               } while (currentTime > mNextTime);
   
               // Make sure this interval doesn't exceed the stop time
               if(mNextTime < mStopTimeInFuture)
                   sendMessageAtTime(obtainMessage(MSG), mNextTime);
               else
                   sendMessageAtTime(obtainMessage(MSG), mStopTimeInFuture);
           }
       }
   }