Flutter定時(shí)器、倒計(jì)時(shí)的快速上手及實(shí)戰(zhàn)講解

const timeout = const Duration(seconds: 5);
print('currentTime='+DateTime.now().toString());
Timer(timeout, () {
 //到時(shí)回調(diào)
 print('afterTimer='+DateTime.now().toString());
});

int count = 0;
const period = const Duration(seconds: 1);
print('currentTime='+DateTime.now().toString());
Timer.periodic(period, (timer) {
 //到時(shí)回調(diào)
 print('afterTimer='+DateTime.now().toString());
 count++;
 if (count >= 5) {
  //取消定時(shí)器，避免無限回調(diào)
  timer.cancel();
  timer = null;
 }
});

//時(shí)間格式化，根據(jù)總秒數(shù)轉(zhuǎn)換為對(duì)應(yīng)的 hh:mm:ss 格式
String constructTime(int seconds) {
 int hour = seconds ~/ 3600;
 int minute = seconds % 3600 ~/ 60;
 int second = seconds % 60;
 return formatTime(hour) + ":" + formatTime(minute) + ":" + formatTime(second);
}

//數(shù)字格式化，將 0~9 的時(shí)間轉(zhuǎn)換為 00~09
String formatTime(int timeNum) {
 return timeNum < 10 ? "0" + timeNum.toString() : timeNum.toString();
}

//獲取當(dāng)期時(shí)間
var now = DateTime.now();
//獲取 2 分鐘的時(shí)間間隔
var twoHours = now.add(Duration(minutes: 2)).difference(now);
//獲取總秒數(shù)，2 分鐘為 120 秒
var seconds = twoHours.inSeconds;
//設(shè)置 1 秒回調(diào)一次
const period = const Duration(seconds: 1);
//打印一開始的時(shí)間格式，為 00:02:00
print(constructTime(seconds));
Timer.periodic(period, (timer) {
 //秒數(shù)減一，因?yàn)橐幻牖卣{(diào)一次
 seconds--;
 //打印減一后的時(shí)間
 print(constructTime(seconds));
 if (seconds == 0) {
  //倒計(jì)時(shí)秒數(shù)為0，取消定時(shí)器
  timer.cancel();
  timer = null;
 }
});

import 'dart:async';

import 'package:flutter/material.dart';

class Countdown extends StatefulWidget {
 @override
 _CountdownState createState() => _CountdownState();
}

class _CountdownState extends State<Countdown> {

 Timer _timer;
 int seconds;

 @override
 Widget build(BuildContext context) {
  return Center(
   child: Text(constructTime(seconds)),
  );
 }

 //時(shí)間格式化，根據(jù)總秒數(shù)轉(zhuǎn)換為對(duì)應(yīng)的 hh:mm:ss 格式
 String constructTime(int seconds) {
  int hour = seconds ~/ 3600;
  int minute = seconds % 3600 ~/ 60;
  int second = seconds % 60;
  return formatTime(hour) + ":" + formatTime(minute) + ":" + formatTime(second);
 }

 //數(shù)字格式化，將 0~9 的時(shí)間轉(zhuǎn)換為 00~09
 String formatTime(int timeNum) {
  return timeNum < 10 ? "0" + timeNum.toString() : timeNum.toString();
 }

 @override
 void initState() {
  super.initState();
  //獲取當(dāng)期時(shí)間
  var now = DateTime.now();
  //獲取 2 分鐘的時(shí)間間隔
  var twoHours = now.add(Duration(minutes: 2)).difference(now);
  //獲取總秒數(shù)，2 分鐘為 120 秒
  seconds = twoHours.inSeconds;
  startTimer();
 }

 void startTimer() {
  //設(shè)置 1 秒回調(diào)一次
  const period = const Duration(seconds: 1);
  _timer = Timer.periodic(period, (timer) {
   //更新界面
   setState(() {
    //秒數(shù)減一，因?yàn)橐幻牖卣{(diào)一次
    seconds--;
   });
   if (seconds == 0) {
    //倒計(jì)時(shí)秒數(shù)為0，取消定時(shí)器
    cancelTimer();
   }
  });
 }

 void cancelTimer() {
  if (_timer != null) {
   _timer.cancel();
   _timer = null;
  }
 }

 @override
 void dispose() {
  super.dispose();
  cancelTimer();
 }
}