最近項目有個需求，就是每個商品列表都有一個倒計時功能，于是乎，用萬能的recyclerview擼了一把，為了方便備忘，在此做個筆記，閑話不多說，直接上demo:

![`Z(PQQHK{0HKRN8Q29%~CI.png

需要注意以下2點：

1.ViewHolder 的重復使用與倒計時顯示沖突。
2.退出應用時釋放所有 CountDownTimer 資源。

Step1.

//適配器
public static class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {

private List<TimerItem> mDatas;
//用于退出activity,避免countdown，造成資源浪費。
private SparseArray<CountDownTimer> countDownMap;

public MyAdapter(Context context, List<TimerItem> datas) {
    mDatas = datas;
    countDownMap = new SparseArray<>();
}

@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item_common, parent, false);
    return new ViewHolder(view);
}

/**
 * 清空資源
 */
public void cancelAllTimers() {
    if (countDownMap == null) {
        return;
    }
    Log.e("TAG",  "size :  " + countDownMap.size());
    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 ViewHolder holder, int position) {
    final TimerItem data = mDatas.get(position);
    holder.statusTv.setText(data.name);
    long time = data.expirationTime;
    time = time - System.currentTimeMillis();
    //將前一個緩存清除
    if (holder.countDownTimer != null) {
        holder.countDownTimer.cancel();
    }
    if (time > 0) {
        holder.countDownTimer = new CountDownTimer(time, 1000) {
            public void onTick(long millisUntilFinished) {
                holder.timeTv.setText(TimeTools.getCountTimeByLong(millisUntilFinished));
                Log.e("TAG", data.name + " :  " + millisUntilFinished);
            }
            public void onFinish() {
                holder.timeTv.setText("00:00:00");
                holder.statusTv.setText(data.name + ":結束");
            }
        }.start();

        countDownMap.put(holder.timeTv.hashCode(), holder.countDownTimer);
    } else {
        holder.timeTv.setText("00:00:00");
        holder.statusTv.setText(data.name + ":結束");
    }

}

@Override
public int getItemCount() {
    if (mDatas != null && !mDatas.isEmpty()) {
        return mDatas.size();
    }
    return 0;
}

public class ViewHolder extends RecyclerView.ViewHolder {
    public TextView statusTv;
    public TextView timeTv;
    public CountDownTimer countDownTimer;

    public ViewHolder(View itemView) {
        super(itemView);
        statusTv = (TextView) itemView.findViewById(R.id.tv_status);
        timeTv = (TextView) itemView.findViewById(R.id.tv_time);
    }
}

}
主要通過 SparseArray<CountDownTimer> 類保存每個 Item 上的 CountDownTimer 類。
當需要復用時，通用 TextView 的 hashCode 取出對應的 CountDownTimer。重新啟動并顯示。
當退出此頁面時，調用 cancelAllTimers() 方法，遍歷 countDownCounters 關閉所有的 CountDownTimer 類。避免造成內存泄漏。

Step2.數據填充

mAdapter = new MyAdapter(mContext,TimerItemUtil.getTimerItemList());
mListView.setAdapter(mAdapter);

Step3.TimerItem 類

public class TimerItem {
//其他屬性
public String name;
//倒計時長，單位毫秒
public long expirationTime;
public TimerItem(String name, long expirationTime) {
    this.name = name;
    this.expirationTime = expirationTime;
}
}

Step4.獲取數據

public static List<TimerItem> getTimerItemList() {
List<TimerItem> lstTimerItems = new ArrayList<>();
lstTimerItems.add(new TimerItem("A", System.currentTimeMillis() + 11 * 1000));
lstTimerItems.add(new TimerItem("B", System.currentTimeMillis() + 22 * 1000));
lstTimerItems.add(new TimerItem("C", System.currentTimeMillis() + 26 * 1000));
lstTimerItems.add(new TimerItem("D", System.currentTimeMillis() + 33 * 1000));
lstTimerItems.add(new TimerItem("E", System.currentTimeMillis() + 24 * 1000));
lstTimerItems.add(new TimerItem("F", System.currentTimeMillis() + 98 * 1000));
lstTimerItems.add(new TimerItem("G", System.currentTimeMillis() + 14 * 1000));
lstTimerItems.add(new TimerItem("H", System.currentTimeMillis() + 36 * 1000));
lstTimerItems.add(new TimerItem("I", System.currentTimeMillis() + 58 * 1000));
lstTimerItems.add(new TimerItem("J", System.currentTimeMillis() + 47 * 1000));
lstTimerItems.add(new TimerItem("K", System.currentTimeMillis() + 66 * 1000));
lstTimerItems.add(new TimerItem("L", System.currentTimeMillis() + 55 * 1000));
lstTimerItems.add(new TimerItem("M", System.currentTimeMillis() + 62 * 1000));
lstTimerItems.add(new TimerItem("N", System.currentTimeMillis() + 45 * 1000));
lstTimerItems.add(new TimerItem("O", System.currentTimeMillis() + 14 * 1000));

return lstTimerItems;

}

Step5.當退出 Activity 時釋放資源

@Override
protected void onDestroy() {
super.onDestroy();
if (mAdapter != null) {
    mAdapter.cancelAllTimers();
}
}

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