public class ChronometerActivity extends Activity implements OnClickListener {
  private Chronometer mChronometer;
  private Button start, stop, reset, format, clear_format;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_chronometer);
    // 初始化View widget
    initViews();
    // 设置监听事件
    initListeners();
  }
  private void initListeners() {
    start.setOnClickListener(this);
    stop.setOnClickListener(this);
    reset.setOnClickListener(this);
    format.setOnClickListener(this);
    clear_format.setOnClickListener(this);
  }
  private void initViews() {
    mChronometer = (Chronometer) findViewById(R.id.chronometer);
    start = (Button) findViewById(R.id.start);
    stop = (Button) findViewById(R.id.stop);
    reset = (Button) findViewById(R.id.reset);
    format = (Button) findViewById(R.id.set_format);
    clear_format = (Button) findViewById(R.id.clear_format);
  }
  View.OnClickListener mStartListener = new OnClickListener() {
    public void onClick(View v) {
      mChronometer.start();
    }
  };
  View.OnClickListener mStopListener = new OnClickListener() {
    public void onClick(View v) {
      mChronometer.stop();
    }
  };
  View.OnClickListener mResetListener = new OnClickListener() {
    public void onClick(View v) {
      mChronometer.setBase(SystemClock.elapsedRealtime());
    }
  };
  View.OnClickListener mSetFormatListener = new OnClickListener() {
    public void onClick(View v) {
      mChronometer.setFormat("Formatted time (%s)");
    }
  };
  View.OnClickListener mClearFormatListener = new OnClickListener() {
    public void onClick(View v) {
      mChronometer.setFormat(null);
    }
  };
  @Override
  public void onClick(View v) {
    switch (v.getId()) {
    case R.id.start:
      mChronometer.start();// 开始计时
      break;
    case R.id.stop:
      mChronometer.stop();// 暂停计时
      break;
    case R.id.reset:
      mChronometer.setBase(SystemClock.elapsedRealtime());// 从开机到现在的毫秒数
      break;
    case R.id.set_format:
      // 需要一个String变量，并使用"%s"表示计时信息
      mChronometer.setFormat("时间累计:%s秒");
      break;
    case R.id.clear_format:
      mChronometer.setFormat(null);
      break;
    }
  }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:gravity="center_horizontal"
  android:orientation="vertical"
  android:padding="10dip" >
  <Chronometer
    android:id="@+id/chronometer"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:format="@string/chronometer_initial_format"
    android:paddingBottom="30dip"
    android:paddingTop="30dip"
    android:textSize="15sp" />
  <Button
    android:id="@+id/start"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="开始" >
    <requestFocus />
  </Button>
  <Button
    android:id="@+id/stop"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="暂停" >
  </Button>
  <Button
    android:id="@+id/reset"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="重新计时" >
  </Button>
  <Button
    android:id="@+id/set_format"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="信息说明" >
  </Button>
  <Button
    android:id="@+id/clear_format"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="取消说明" >
  </Button>
</LinearLayout>