最近在做一个项目，需要用到列表倒计时功能，捣鼓半天终于弄了出来，在安卓中实现这个效果需要用到Countdowntimer,通过这个类的使用，不仅可以实现倒计时的效果，还可以完美解决在实现倒计时过程中的两个bug。

1.内存问题

2.由于recyclerview的item复用导致不同条目的时间错乱

首先看下实现的最终效果

如何显示列表我相信大家都会，这里我只附上和倒计时功能实现的adapter类。

public class ClockAdapter extends RecyclerView.Adapter {

private SparseArray countDownMap = new SparseArray<>();

@Override

public ClockViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_rv, parent, false);

return new ClockViewHolder(view);

}

/**

* 清空资源

*/

public void cancelAllTimers() {

if (countDownMap == null) {

return;

}

for (int i = 0,length = countDownMap.size(); i < length; i++) {

CountDownTimer cdt = countDownMap.get(countDownMap.keyAt(i));

if (cdt != null) {

cdt.cancel();

}

}

}

@Override

public void onBindViewHolder(final ClockViewHolder holder, int position) {

long betweenDate;

if (position == 0) {

betweenDate= DateUtil.getLeftTime("2017-8-8 12:10:10");

} else {

betweenDate= DateUtil.getLeftTime("2017-8-9 15:10:10");

}

if (holder.countDownTimer != null) {

holder.countDownTimer.cancel();

}

if (betweenDate > 0) {

holder.countDownTimer = new CountDownTimer(betweenDate, 1000) {

public void onTick(long millisUntilFinished) {

millisUntilFinished = millisUntilFinished / 1000;

int hours = (int) (millisUntilFinished / (60 * 60));

int leftSeconds = (int) (millisUntilFinished % (60 * 60));

int minutes = leftSeconds / 60;

int seconds = leftSeconds % 60;

final StringBuffer sBuffer = new StringBuffer();

sBuffer.append(addZeroPrefix(hours));

sBuffer.append(":");

sBuffer.append(addZeroPrefix(minutes));

sBuffer.append(":");

sBuffer.append(addZeroPrefix(seconds));

holder.clock.setText(sBuffer.toString());

}

public void onFinish() {

// 时间结束后进行相应逻辑处理

}

}.start();

countDownMap.put(holder.clock.hashCode(), holder.countDownTimer);

} else {

// 时间结束 进行相应逻辑处理

}

}

@Override

public int getItemCount() {

return 25;

}

class ClockViewHolder extends RecyclerView.ViewHolder {

TextView clock;

CountDownTimer countDownTimer;

public ClockViewHolder(View itemView) {

super(itemView);

clock = (TextView) itemView.findViewById(R.id.clock);

}

}

}

其中cancelAllTimer()这个方法解决了内存的问题，通过这行代码，将item的hashcode作为key设入SparseArray中，这样在cancelAllTimer方法中可以一个一个取出来进行倒计时取消操作。

countDownMap.put(holder.clock.hashCode(),holder.countDownTimer);

接着通过下面这行代码新建一个CountDownTimer类

holder.countDownTimer = new CountDownTimer(betweenDate, 1000) {

public void onTick(long millisUntilFinished) {

millisUntilFinished = millisUntilFinished / 1000;

int hours = (int) (millisUntilFinished / (60 * 60));

int leftSeconds = (int) (millisUntilFinished % (60 * 60));

int minutes = leftSeconds / 60;

int seconds = leftSeconds % 60;

final StringBuffer sBuffer = new StringBuffer();

sBuffer.append(addZeroPrefix(hours));

sBuffer.append(":") sBuffer.append(addZeroPrefix(minutes));

sBuffer.append(":");

sBuffer.append(addZeroPrefix(seconds));

holder.clock.setText(sBuffer.toString());

}

public void onFinish() {

// 时间结束后进行相应逻辑处理

}

}.start();

分析它的源码

public CountDownTimer(long millisInFuture, long countDownInterval) {

mMillisInFuture = millisInFuture;

mCountdownInterval = countDownInterval;

}

从中可以很清楚的看出，设置了两个值，第一个是倒计时结束时间，第二个是刷新时间的间隔时间。

然后通过start方法进行启动，接着看下start方法中进行的处理

public synchronized final CountDownTimer start() {

mCancelled = false;

if (mMillisInFuture <= 0) {

onFinish();

return this;

}

mStopTimeInFuture = SystemClock.elapsedRealtime() + mMillisInFuture;

mHandler.sendMessage(mHandler.obtainMessage(MSG));

return this;

}

源码中，当倒计时截止时间小于等0时也就是倒计时结束时，调用了onFinish方法，若时间还未结束，则通过handler的异步消息机制，将消息进行发出，通过一整个流程，最终方法会走到handler的handleMessage方法中，如果有不熟悉这个异步流程的伙伴，可以去看我以前写的一篇异步消息机制的文章 android异步消息机制，源码层面彻底解析。好了，接下来就来看看handler的handleMessage方法。

private Handler mHandler = new Handler() {

@Override

public void handleMessage(Message msg) {

synchronized (CountDownTimer.this) {

if (mCancelled) {

return;

}

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

if (millisLeft <= 0) {

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 = lastTickStart + mCountdownInterval - SystemClock.elapsedRealtime();

// special case: user's onTick took more than interval to

// complete, skip to next interval

while (delay < 0) delay += mCountdownInterval;

sendMessageDelayed(obtainMessage(MSG), delay);

}

}

}

};

相信这段源码还是很通熟易懂，首先计算出剩余时间，如果剩余时间小于刷新时间，就发送一条延时消息直到时间结束，如果剩余时间大于刷新时间就调用onTick(millisLeft)方法，这个方法在我们创建CountDownTimer类时就进行过重写，在里面就可以写我们倒计时展示的具体逻辑了。至此整个流程结束。

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。