Android CountDownTimer重写

CountDownTimerRew 是一个可重写、动态修改计时时间的 Android 倒计时器类。它允许开发者设置倒计时总时长、间隔时间，并通过 onTick 和 onFinish 方法实现定时回调。该类支持动态修改计时参数，如 millisInFuture 和 countDownInterval，并提供了 cancel 和 start 方法控制计时器的启停。通过 WeakHandler 类，CountDownTimerRew 避免了内存泄漏问题。使用时，开发者只需继承该类并实现 onTick 和 onFinish 方法即可。

CountDownTimerRew 类

public abstract class CountDownTimerRew {

    /**
     * Millis since epoch when alarm should stop.
     */
    private long mMillisInFuture;

    /**
     * The interval in millis that the user receives callbacks
     */
    private long mCountdownInterval;

    private long mStopTimeInFuture;

    /**
     * boolean representing if the timer was cancelled
     */
    private boolean mCancelled = false;

    private Object mTag;

    /**
     * @param millisInFuture    The number of millis in the future from the call
     *                          to {@link #start()} until the countdown is done and {@link #onFinish()}
     *                          is called.
     * @param countDownInterval The interval along the way to receive
     *                          {@link #onTick(long, Object)} callbacks.
     */
    public CountDownTimerRew(long millisInFuture, long countDownInterval) {
        mMillisInFuture = millisInFuture;
        mCountdownInterval = countDownInterval;
    }

    public CountDownTimerRew setTag(Object mTag) {
        this.mTag = mTag;
        return this;
    }

    public CountDownTimerRew setMillisInFuture(long mMillisInFuture) {
        this.mMillisInFuture = mMillisInFuture;
        return this;
    }

    public CountDownTimerRew setCountdownInterval(long mCountdownInterval) {
        this.mCountdownInterval = mCountdownInterval;
        return this;
    }

    /**
     * Cancel the countdown.
     */
    public synchronized final void cancel() {
        mCancelled = true;
        mHandler.removeMessages(MSG);
    }

    /**
     * Start the countdown.
     */
    public synchronized final CountDownTimerRew start() {
        mCancelled = false;
        if (mMillisInFuture <= 0) {
            onFinish();
            return this;
        }
        mStopTimeInFuture = SystemClock.elapsedRealtime() + mMillisInFuture;
        mHandler.sendMessage(mHandler.obtainMessage(MSG));
        return this;
    }


    /**
     * Callback fired on regular interval.
     *
     * @param millisUntilFinished The amount of time until finished.
     */
    public abstract void onTick(long millisUntilFinished, Object mTag);

    /**
     * Callback fired when the time is up.
     */
    public abstract void onFinish();


    private static final int MSG = 1;


    // handles counting down
    private final Handler mHandler = new WeakHandler(Looper.getMainLooper()) {

        @Override
        public void handleMessage(@NonNull Message msg) {
            synchronized (CountDownTimerRew.this) {
                if (mCancelled) {
                    return;
                }

                final long millisLeft = mStopTimeInFuture - SystemClock.elapsedRealtime();

                if (millisLeft <= 0) {
                    onFinish();
                } else {
                    long lastTickStart = SystemClock.elapsedRealtime();
                    onTick(millisLeft, mTag);

                    // take into account user's onTick taking time to execute
                    long lastTickDuration = SystemClock.elapsedRealtime() - lastTickStart;
                    long delay;

                    if (millisLeft < mCountdownInterval) {
                        // just delay until done
                        delay = millisLeft - lastTickDuration;

                        // special case: user's onTick took more than interval to
                        // complete, trigger onFinish without delay
                        if (delay < 0) delay = 0;
                    } else {
                        delay = mCountdownInterval - lastTickDuration;

                        // special case: user's onTick took more than interval to
                        // complete, skip to next interval
                        while (delay < 0) delay += mCountdownInterval;
                    }

                    sendMessageDelayed(obtainMessage(MSG), delay);
                }
            }
        }
    };
}

WeakHandler类

public class WeakHandler extends Handler {
    private WeakReference<Activity> mActivity;

    public WeakHandler() {
        this(Looper.getMainLooper(), null);
    }

    public WeakHandler(@NonNull Looper looper) {
        this(looper, null);
    }

    public WeakHandler(@NonNull Looper looper, Activity mActivity) {
        super(looper);
        setActivity(mActivity);
    }

    public WeakReference<Activity> getActivity() {
        return mActivity;
    }

    public void setActivity(Activity mActivity) {
        this.mActivity = new WeakReference<>(mActivity);
    }
}

使用方法

    private CountDownTimerRew mCountDownTimerRew;

    public CountDownTimerRew getCountDownTimerRew() {
        if (null == mCountDownTimerRew)
            mCountDownTimerRew = new CountDownTimerRew(5000, 1000) {
                @Override
                public void onTick(long millisUntilFinished, Object mTag) {
                    int iSeconds = (int) (millisUntilFinished / 1000);

                    int iTag = mTag instanceof Integer ? (int) mTag : -1;
                    if (iTag == 0) {
                    //TODO
                    }
                }

                @Override
                public void onFinish() {
                }
            };
        return mCountDownTimerRew;
    }

//启动计时器
getCountDownTimerRew().setMillisInFuture(180000).setMillisInFuture(500).setTag(0).start();
//取消计时器
getCountDownTimerRew().cancel();