Android：如何暂停和恢复倒数计时器？

// Adapted from Android's CountDownTimer classpackage com.cycleindex.multitimer;import android.os.Handler;import android.os.Message;import android.os.SystemClock;public abstract class CountDownTimerWithPause {      private long mStopTimeInFuture;      private long mMillisInFuture;        private final long mTotalCountdown;        private final long mCountdownInterval;        private long mPauseTimeRemaining;        private boolean mRunAtStart;        public CountDownTimerWithPause(long millisOnTimer, long countDownInterval, boolean runAtStart) {        mMillisInFuture = millisOnTimer;        mTotalCountdown = mMillisInFuture;        mCountdownInterval = countDownInterval;        mRunAtStart = runAtStart;    }        public final void cancel() {        mHandler.removeMessages(MSG);    }        public synchronized final CountDownTimerWithPause create() {        if (mMillisInFuture <= 0) { onFinish();        } else {          mPauseTimeRemaining = mMillisInFuture;        }        if (mRunAtStart) {          resume();        }        return this;    }      public void pause () {    if (isRunning()) {      mPauseTimeRemaining = timeLeft();      cancel();    }  }    public void resume () {    if (isPaused()) {      mMillisInFuture = mPauseTimeRemaining;      mStopTimeInFuture = SystemClock.elapsedRealtime() + mMillisInFuture;          mHandler.sendMessage(mHandler.obtainMessage(MSG));      mPauseTimeRemaining = 0;    }  }    public boolean isPaused () {    return (mPauseTimeRemaining > 0);  }    public boolean isRunning() {    return (! isPaused());  }    public long timeLeft() {    long millisUntilFinished;    if (isPaused()) {      millisUntilFinished = mPauseTimeRemaining;    } else {      millisUntilFinished = mStopTimeInFuture - SystemClock.elapsedRealtime();      if (millisUntilFinished < 0) millisUntilFinished = 0;    }    return millisUntilFinished;  }    public long totalCountdown() {    return mTotalCountdown;  }    public long timePassed() {    return mTotalCountdown - timeLeft();  }    public boolean hasBeenStarted() {    return (mPauseTimeRemaining <= mMillisInFuture);  }        public abstract void onTick(long millisUntilFinished);        public abstract void onFinish();    private static final int MSG = 1;    // handles counting down    private Handler mHandler = new Handler() {        @Override        public void handleMessage(Message msg) { synchronized (CountDownTimerWithPause.this) {     long millisLeft = timeLeft();     if (millisLeft <= 0) {         cancel();       onFinish();     } else if (millisLeft < mCountdownInterval) {         // no tick, just delay until done         sendMessageDelayed(obtainMessage(MSG), millisLeft);     } else {         long lastTickStart = SystemClock.elapsedRealtime();         onTick(millisLeft);         // take into account user's onTick taking time to execute         long delay = mCountdownInterval - (SystemClock.elapsedRealtime() - lastTickStart);         // special case: user's onTick took more than mCountdownInterval to         // complete, skip to next interval         while (delay < 0) delay += mCountdownInterval;         sendMessageDelayed(obtainMessage(MSG), delay);     } }        }    };}

资料来源：本要点。