RecyclerView实现列表倒计时
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<ClockAdapter.ClockViewHolder> { private SparseArray<CountDownTimer> 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。
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