最近面试时，面试官问了一个列表倒计时效果如何实现，现在记录一下。

运行效果图

实现思路

实现方法主要有两个：
1.为每个开始倒计时的item启动一个定时器，再做更新item处理；
2.只启动一个定时器，然后遍历数据，再做再做更新item处理。
经过思考，包括性能、实现等方面，决定使用第2种方式实现。

实现过程

数据实体

/** * 总共的倒计时的时间(结束时间-开始时间),单位：毫秒 * 例: 2019-02-23 11:00:30 与 2019-02-23 11:00:00 之间的相差的毫秒数 */ private long totalTime; /** * 倒计时是否在暂停状态 */ private boolean isPause = true;

倒计时

Timer

mTimer.schedule(mTask, 0, 1000);

TimerTask

class MyTask extends TimerTask { @Override public void run() { if (mList.isEmpty()) { return; } int size = mList.size(); CountDownTimerBean bean; long totalTime; for (int i = 0; i < size; i++) { bean = mList.get(i); if (!bean.isPause()) {//不处于暂停状态 totalTime = bean.getTotalTime() - 1000; if (totalTime <= 0) { bean.setPause(true); bean.setTotalTime(0); } bean.setTotalTime(totalTime); Message message = mHandler.obtainMessage(1); message.arg1 = i; mHandler.sendMessage(message); } } } }

线程交互更新item

mHandler = new Handler(Looper.getMainLooper()) { @Override public void handleMessage(Message msg) { switch (msg.what) { case 1: notifyItemChanged(msg.arg1, "update-time"); break; } } };

性能优化方面

1.调用notifyItemChanged()方法后，不要更新整个item(比如说item包含图片，不需要变的)，所以要重写onBindViewHolder( Holder , int , List )方法：

@Override public void onBindViewHolder(@NonNull Holder holder, int position, @NonNull List<Object> payloads) { if (payloads.isEmpty()) { onBindViewHolder(holder, position); return; } //更新某个控件,比如说只需要更新时间信息，其他不用动 CountDownTimerBean bean = mList.get(position); long day = bean.getTotalTime() / (1000 * 60 * 60 * 24); long hour = (bean.getTotalTime() / (1000 * 60 * 60) - day * 24); long min = ((bean.getTotalTime() / (60 * 1000)) - day * 24 * 60 - hour * 60); long s = (bean.getTotalTime() / 1000 - day * 24 * 60 * 60 - hour * 60 * 60 - min * 60); holder.tvTime.setText("剩余时间: " + day + "天" + hour + "小时" + min + "分" + s + "秒"); holder.btnAction.setText(bean.isPause() ? "开始" : "暂停"); holder.btnAction.setEnabled(bean.getTotalTime() != 0); }

2.销毁资源操作：

/** * 销毁资源 */ public void destroy() { mHandler.removeMessages(1); if (mTimer != null) { mTimer.cancel(); mTimer.purge(); mTimer = null; } }

RecyclerView.Adapter部分源码

public class CountDownTimerAdapter extends RecyclerView.Adapter<CountDownTimerAdapter.Holder> { private static final String TAG = "CountDownTimerAdapter->"; private List<CountDownTimerBean> mList;//数据 private Handler mHandler;//线程调度，用来更新列表 private Timer mTimer; private MyTask mTask; public CountDownTimerAdapter() { mList = new ArrayList<>(); mHandler = new Handler(Looper.getMainLooper()) { @Override public void handleMessage(Message msg) { switch (msg.what) { case 1: notifyItemChanged(msg.arg1, "update-time"); break; } } }; mTask = new MyTask(); } public void bindAdapterToRecyclerView(@NonNull RecyclerView view) { view.setAdapter(this); } /** * 设置新的数据源 * * @param list 数据 */ public void setNewData(@NonNull List<CountDownTimerBean> list) { destroy(); mList.clear(); mList.addAll(list); notifyDataSetChanged(); if (mTimer == null) { mTimer = new Timer(); } mTimer.schedule(mTask, 0, 1000); } /** * 销毁资源 */ public void destroy() { mHandler.removeMessages(1); if (mTimer != null) { mTimer.cancel(); mTimer.purge(); mTimer = null; } } @NonNull @Override public Holder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) { View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.item_count_down_timer, viewGroup, false); return new Holder(view); } @Override public void onBindViewHolder(@NonNull Holder holder, int position, @NonNull List<Object> payloads) { if (payloads.isEmpty()) { onBindViewHolder(holder, position); return; } //更新某个控件,比如说只需要更新时间信息，其他不用动 CountDownTimerBean bean = mList.get(position); long day = bean.getTotalTime() / (1000 * 60 * 60 * 24); long hour = (bean.getTotalTime() / (1000 * 60 * 60) - day * 24); long min = ((bean.getTotalTime() / (60 * 1000)) - day * 24 * 60 - hour * 60); long s = (bean.getTotalTime() / 1000 - day * 24 * 60 * 60 - hour * 60 * 60 - min * 60); holder.tvTime.setText("剩余时间: " + day + "天" + hour + "小时" + min + "分" + s + "秒"); holder.btnAction.setText(bean.isPause() ? "开始" : "暂停"); holder.btnAction.setEnabled(bean.getTotalTime() != 0); } @Override public void onBindViewHolder(@NonNull final Holder holder, int position) { holder.ivIcon.setImageResource(R.mipmap.ic_launcher_round); final CountDownTimerBean bean = mList.get(position); long day = bean.getTotalTime() / (1000 * 60 * 60 * 24); long hour = (bean.getTotalTime() / (1000 * 60 * 60) - day * 24); long min = ((bean.getTotalTime() / (60 * 1000)) - day * 24 * 60 - hour * 60); long s = (bean.getTotalTime() / 1000 - day * 24 * 60 * 60 - hour * 60 * 60 - min * 60); holder.tvTime.setText("剩余时间: " + day + "天" + hour + "小时" + min + "分" + s + "秒"); holder.btnAction.setText(bean.isPause() ? "开始" : "暂停"); holder.btnAction.setEnabled(bean.getTotalTime() != 0); holder.btnAction.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { if (bean.isPause()) { bean.setPause(false); holder.btnAction.setText("暂停"); } else { bean.setPause(true); holder.btnAction.setText("开始"); } } }); } @Override public int getItemCount() { return mList.size(); } class Holder extends RecyclerView.ViewHolder { private ImageView ivIcon; private TextView tvTime; private Button btnAction; Holder(@NonNull View itemView) { super(itemView); ivIcon = itemView.findViewById(R.id.iv_icon); tvTime = itemView.findViewById(R.id.tv_time); btnAction = itemView.findViewById(R.id.btn_action); } } class MyTask extends TimerTask { @Override public void run() { if (mList.isEmpty()) { return; } int size = mList.size(); CountDownTimerBean bean; long totalTime; for (int i = 0; i < size; i++) { bean = mList.get(i); if (!bean.isPause()) {//不处于暂停状态 totalTime = bean.getTotalTime() - 1000; if (totalTime <= 0) { bean.setPause(true); bean.setTotalTime(0); } bean.setTotalTime(totalTime); Message message = mHandler.obtainMessage(1); message.arg1 = i; mHandler.sendMessage(message); } } } }}

项目地址：Android利用RecyclerView实现列表倒计时效果

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