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

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();
     }
 };
}

To start the chronometer you should use the setBase() method of your chronometer with SystemClock.elapsedRealTime(). Just like this:

mChronometer.setBase(SystemClock.elapsedRealTime())

But if you want to start at another time, you have to subtract the time you want in milliseconds. For example, you want to start your Chronometer at 10 seconds:

mChronometer.setBase(SystemClock.elapsedRealTime() - 10*1000);

At 2 minutes:

mChronometer.setBase(SystemClock.elapsedRealTime() - 2*60*1000);

But the problem here is that the Chronometer will show "00:00" time before it start to count, to change it to your time you have to do that :

mChronometer.setText("02:00");

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.

This works for me :

Date now = new Date();
long elapsedTime = now.getTime() - startTime.getTime(); //startTime is whatever time you want to start the chronometer from. you might have stored it somwehere
myChronometer.setBase(SystemClock.elapsedRealtime() - elapsedTime);
myChronometer.start();