Android: chronometer as a persistent stopwatch. How to set starting time? What is Chronometer "Base"?

Question

Hi!

I do have one service running in the background. Whenever it starts I store in memory the starting time in milliseconds:

startingTime = new Date().getTime();

I want to display a chronometer that starts counting when the service starts and never stops until the user presses a button. I want to allow the user to leave the activity rendering the chronometer, do some stuff and then return. But the idea is that when the user returns I dont want the chronometer to go to 0:00 again. Insted I want it to show the exact time that has passed ever since the service has started.

I can calculate elapsedTime every time the user return to the chronometer activity:

elapsedTime =  new Date().getTime() - startingTime;

The thing is that i dont know how to tell the chronometer to start counting from that time!

Setting it as the chronometer base does not work. Can someon explain what exactly "base" means or how to accomplish this?

thanks a lot! BYE

Answer 1

You can use Chronometer.

You should also check this thread.

EDIT: The solution:

public class ChronoExample extends Activity {
 Chronometer mChronometer;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);

     LinearLayout layout = new LinearLayout(this);
     layout.setOrientation(LinearLayout.VERTICAL);

     mChronometer = new Chronometer(this);

     // Set the initial value
     mChronometer.setText("00:10");
     layout.addView(mChronometer);

     Button startButton = new Button(this);
     startButton.setText("Start");
     startButton.setOnClickListener(mStartListener);
     layout.addView(startButton);

     Button stopButton = new Button(this);
     stopButton.setText("Stop");
     stopButton.setOnClickListener(mStopListener);
     layout.addView(stopButton);

     Button resetButton = new Button(this);
     resetButton.setText("Reset");
     resetButton.setOnClickListener(mResetListener);
     layout.addView(resetButton);        

     setContentView(layout);
 }

 private void showElapsedTime() {
     long elapsedMillis = SystemClock.elapsedRealtime() - mChronometer.getBase();            
     Toast.makeText(ChronoExample.this, "Elapsed milliseconds: " + elapsedMillis, 
             Toast.LENGTH_SHORT).show();
 }

 View.OnClickListener mStartListener = new OnClickListener() {
     public void onClick(View v) {
      int stoppedMilliseconds = 0;

         String chronoText = mChronometer.getText().toString();
         String array[] = chronoText.split(":");
         if (array.length == 2) {
           stoppedMilliseconds = Integer.parseInt(array[0]) * 60 * 1000
               + Integer.parseInt(array[1]) * 1000;
         } else if (array.length == 3) {
           stoppedMilliseconds = Integer.parseInt(array[0]) * 60 * 60 * 1000 
               + Integer.parseInt(array[1]) * 60 * 1000
               + Integer.parseInt(array[2]) * 1000;
         }

         mChronometer.setBase(SystemClock.elapsedRealtime() - stoppedMilliseconds);
         mChronometer.start();
     }
 };

 View.OnClickListener mStopListener = new OnClickListener() {
     public void onClick(View v) {
         mChronometer.stop();
         showElapsedTime();
     }
 };

 View.OnClickListener mResetListener = new OnClickListener() {
     public void onClick(View v) {
         mChronometer.setBase(SystemClock.elapsedRealtime());
         showElapsedTime();
     }
 };
}

Answer 2

The base time is the time that the Chronometer started ticking at. You can set it using Chronometer.setBase(). You should get the base time by using SystemClock.getElapsedTime(). Call setBase() with the start time each time the Chronometer is started. If there is potential for the Activity to be destroyed and recreated while the timer is still active then you will need to hold the base time somewhere outside of the Activity that owns the Chronometer.

Answer 3

Hey guys, thanks a lot to both of you. I couldnt understand what base meant and I would have never figured out to use SystemClock.elapsedRealtime(). So thanks again!