《 Dart 语言》课件 CH09-06-案例0906-Stream和StreamController综合应用

案例：Stream和StreamController综合应用Dart库案例描述设计一个案例，演示综合利用Stream

和StreamController实现异步的原理和方法。知识要点Duration类是

dart:core

库中的一个类，表示从一个时间点到另一个时间点的时差。DurationDuration({intdays=0,//天数

inthours=0,//小时数

intminutes=0,//分钟数

intseconds=0,//秒数

intmilliseconds=0,//毫秒数

intmicroseconds=0,//微秒数})构造函数知识要点示例-1：constfastestMarathon=Duration(hours:2,minutes:3,seconds:2);print(fastestMarathon.inDays);//0print(fastestMarathon.inHours);//2print(fastestMarathon.inMinutes);//123print(fastestMarathon.inSeconds);//7382print(fastestMarathon.inMilliseconds);//7382000知识要点constoverDayAgo=Duration(days:-1,hours:-10);print(overDayAgo.inDays);//-1print(overDayAgo.inHours);//-34print(overDayAgo.inMinutes);//-2040示例-2：知识要点constfirstHalf=Duration(minutes:45);//00:45:00.000000constsecondHalf=Duration(minutes:45);//00:45:00.000000constoverTime=Duration(minutes:30);//00:30:00.000000finalmaxGameTime=firstHalf+secondHalf+overTime;print(maxGameTime.inMinutes);//120varresult=firstHalf.compareTo(secondHalf);//0result=overTime.compareTo(firstHalf);//-1result=secondHalf.compareTo(overTime);//1示例-3：知识要点Timer倒计时器类属于

dart:async

库，可配置为触发一次或多次。Timer.periodic命名构造函数用于创建一个重复的计时器。TimerTimer.periodic(Durationduration,voidFunction(Timer)callback)知识要点varcounter=3;Timer.periodic(constDuration(seconds:2),(timer){print(timer.tick);//最新计时器事件之前的持续时间数

counter--;

if(counter==0){

print('Cancelt