RecyclerView實(shí)現(xiàn)列表倒計(jì)時(shí)

來(lái)源：本站原創(chuàng)|時(shí)間：2020-01-10|欄目：Android|點(diǎn)擊：次

最近在做一個(gè)項(xiàng)目，需要用到列表倒計(jì)時(shí)功能，搗鼓半天終于弄了出來(lái)，在安卓中實(shí)現(xiàn)這個(gè)效果需要用到Countdowntimer,通過(guò)這個(gè)類(lèi)的使用，不僅可以實(shí)現(xiàn)倒計(jì)時(shí)的效果，還可以完美解決在實(shí)現(xiàn)倒計(jì)時(shí)過(guò)程中的兩個(gè)bug。

1.內(nèi)存問(wèn)題
2.由于recyclerview的item復(fù)用導(dǎo)致不同條目的時(shí)間錯(cuò)亂

首先看下實(shí)現(xiàn)的最終效果

如何顯示列表我相信大家都會(huì)，這里我只附上和倒計(jì)時(shí)功能實(shí)現(xiàn)的adapter類(lèi)。

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);
 }
 /**
  * 清空資源
  */
 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() {
//     時(shí)間結(jié)束后進(jìn)行相應(yīng)邏輯處理
    }
   }.start();
   countDownMap.put(holder.clock.hashCode(), holder.countDownTimer);
  } else {
//   時(shí)間結(jié)束 進(jìn)行相應(yīng)邏輯處理
  }


 }

 @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()這個(gè)方法解決了內(nèi)存的問(wèn)題，通過(guò)這行代碼，將item的hashcode作為key設(shè)入SparseArray中，這樣在cancelAllTimer方法中可以一個(gè)一個(gè)取出來(lái)進(jìn)行倒計(jì)時(shí)取消操作。

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

接著通過(guò)下面這行代碼新建一個(gè)CountDownTimer類(lèi)

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() {
// 時(shí)間結(jié)束后進(jìn)行相應(yīng)邏輯處理
}
}.start();

分析它的源碼

public CountDownTimer(long millisInFuture, long countDownInterval) {
  mMillisInFuture = millisInFuture;
  mCountdownInterval = countDownInterval;
 }

從中可以很清楚的看出，設(shè)置了兩個(gè)值，第一個(gè)是倒計(jì)時(shí)結(jié)束時(shí)間，第二個(gè)是刷新時(shí)間的間隔時(shí)間。
然后通過(guò)start方法進(jìn)行啟動(dòng)，接著看下start方法中進(jìn)行的處理

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

源碼中，當(dāng)?shù)褂?jì)時(shí)截止時(shí)間小于等0時(shí)也就是倒計(jì)時(shí)結(jié)束時(shí)，調(diào)用了onFinish方法，若時(shí)間還未結(jié)束，則通過(guò)handler的異步消息機(jī)制，將消息進(jìn)行發(fā)出，通過(guò)一整個(gè)流程，最終方法會(huì)走到handler的handleMessage方法中，如果有不熟悉這個(gè)異步流程的伙伴，可以去看我以前寫(xiě)的一篇異步消息機(jī)制的文章 android異步消息機(jī)制，源碼層面徹底解析。好了，接下來(lái)就來(lái)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);
    }
   }
  }
 };

相信這段源碼還是很通熟易懂，首先計(jì)算出剩余時(shí)間，如果剩余時(shí)間小于刷新時(shí)間，就發(fā)送一條延時(shí)消息直到時(shí)間結(jié)束，如果剩余時(shí)間大于刷新時(shí)間就調(diào)用onTick(millisLeft)方法，這個(gè)方法在我們創(chuàng)建CountDownTimer類(lèi)時(shí)就進(jìn)行過(guò)重寫(xiě)，在里面就可以寫(xiě)我們倒計(jì)時(shí)展示的具體邏輯了。至此整個(gè)流程結(jié)束。

以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持我們。

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