前言
最近面试时，面试官问了一个列表倒计时效果如何实现，然后脑袋突然懵的了O(∩_∩)O，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
代码语言：javascript复制/**
* 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
代码语言：javascript复制mTimer.schedule(mTask, 0, 1000);TimerTask
代码语言：javascript复制 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
代码语言：javascript复制 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
代码语言：javascript复制@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：
代码语言：javascript复制 /**
* 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
代码语言：javascript复制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
源码
总结
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