Flutter CustomTimerPainter 我们如何在后台运行它，这样计时器就不会在处理时停止

Question

这是 myclass 的完整代码我在这里尝试做的是我正在运行一个计时器，当计时器达到 0 时它会显示一个广告，但是当应用程序关闭时，计时器也停止了无论如何计时器运行在后台以及不要停止。我试过把String _ab = '45'; 保存它的状态，但它没有工作，它只是节省了剩余的时间，但是当应用程序关闭时，计时器也停在那里，谷歌了很多但没有找到任何解决方案。在这方面的帮助会非常好

import 'dart:math' as math;
import 'package:flutter/material.dart';
import 'package:firebase_admob/firebase_admob.dart';


class Showads extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: CountDownTimer(),
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        iconTheme: IconThemeData(
          color: Colors.white,
        ),
        accentColor: Colors.red,
      ),
    );
  }
}

const String testDevice = 'MobileId';

class CountDownTimer extends StatefulWidget {
  @override
  _CountDownTimerState createState() => _CountDownTimerState();
}
String _ab = '45';
class _CountDownTimerState extends State<CountDownTimer>
    with TickerProviderStateMixin {

static const MobileAdTargetingInfo targetingInfo = MobileAdTargetingInfo(
    testDevices: testDevice != null ? <String>[testDevice] : null,
    nonPersonalizedAds: true,
    keywords: <String>['Game', 'Mario'],
  );

  InterstitialAd _interstitialAd;
  RewardedVideoAd videoAd = RewardedVideoAd.instance;
  bool _interstialadValue = false;

  InterstitialAd createInterstitialAd() {
    return InterstitialAd(
        adUnitId: InterstitialAd.testAdUnitId,
      //Change Interstitial AdUnitId with Admob ID
        targetingInfo: targetingInfo,
        listener: (MobileAdEvent event) {
          print("IntersttialAd $event");
        });
  }
      int _coins =0;
  @override
  void initState() {
    FirebaseAdMob.instance.initialize(appId: FirebaseAdMob.testAppId);
    //Change appId With Admob Id
     videoAd.listener =
      (RewardedVideoAdEvent event, {String rewardType, int rewardAmount}) {
    print("REWARDED VIDEO AD $event");
    if (event == RewardedVideoAdEvent.rewarded) {
      setState(() {
        _coins += rewardAmount;
      });
    }
  };

  videoAd.load(
    adUnitId: RewardedVideoAd.testAdUnitId,
    targetingInfo: targetingInfo);

    super.initState();
     if(_ab == '00'){
      setState(() {
        _ab ='40';
      });
    }
    controller = AnimationController(
      vsync: this,
      duration: Duration(seconds: int.parse(_ab)),
      );
  }


  @override
  void dispose() {
    if(_ab == '00'){
      setState(() {
        _ab ='40';
      });
    }
    print(timerString);
    print(timerString.substring(2, 4));

    setState(() => _ab = timerString.substring(2, 4));
    print(_ab);
    setState(() =>  controller);
    _CountDownTimerState().dispose();
    controller.dispose();
    if(_interstialadValue){
    _interstitialAd.dispose();
    }
    super.dispose();
  }

  AnimationController controller;

  String get timerString {
    Duration duration = controller.duration * controller.value;
    return '${duration.inMinutes}:${(duration.inSeconds % 60).toString().padLeft(2, '0')}';
  }

  @override
  Widget build(BuildContext context) {
    ThemeData themeData = Theme.of(context);
    return Scaffold(
      backgroundColor: Colors.black,
      body: AnimatedBuilder(
          animation: controller,
          builder: (context, child) {
            return Stack(
              children: <Widget>[
                Align(
                  alignment: Alignment.bottomCenter,
                  child:
                  Container(
                    color: Colors.amber,
                    height:
                    controller.value * MediaQuery.of(context).size.height,
                  ),
                ),
                Padding(
                  padding: EdgeInsets.all(8.0),
                  child: Column(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: <Widget>[
                      Expanded(
                        child: Align(
                          alignment: FractionalOffset.center,
                          child: AspectRatio(
                            aspectRatio: 1.0,
                            child: Stack(
                              children: <Widget>[
                                Positioned.fill(
                                  child: CustomPaint(
                                      painter: CustomTimerPainter(
                                        animation: controller,
                                        backgroundColor: Colors.white,
                                        color: themeData.indicatorColor,
                                      )),
                                ),
                                Align(
                                  alignment: FractionalOffset.center,
                                  child: Column(
                                    mainAxisAlignment:
                                    MainAxisAlignment.spaceEvenly,
                                    crossAxisAlignment:
                                    CrossAxisAlignment.center,
                                    children: <Widget>[
                                      Text(
                                        "Next AD Timer ",
                                        style: TextStyle(
                                            fontSize: 20.0,
                                            color: Colors.white),
                                      ),
                                      Text(
                                        "Minimize App \n Do not close",
                                        style: TextStyle(
                                            fontSize: 20.0,
                                            color: Colors.white),
                                      ),
                                      Text(
                                        timerString,
                                        style: TextStyle(
                                            fontSize: 112.0,
                                            color: Colors.white),
                                      ),
                                    ],
                                  ),
                                ),
                              ],
                            ),
                          ),
                        ),
                      ),
                      AnimatedBuilder(
                          animation: controller,
                          builder: (context, child) {
                            return FloatingActionButton.extended(
                                onPressed: () {
                                  if (controller.isAnimating) {
                                    //controller.stop();
                                     createInterstitialAd()
                                      ..load()
                                      ..show();
                                      setState(() {
                                        _interstialadValue = true;
                                        print(controller.value);
                                        print(timerString);
                                      });
                                  }
                                  else {
                                   // videoAd.show();
                                   showRewardedAd();

                                   // Checkout();
                                    controller.reverse(
                                        from: controller.value == 0.0
                                            ? 1.0
                                            : controller.value);
                                  }
                                },
                                icon: Icon(controller.isAnimating
                                    ? Icons.pause
                                    : Icons.play_arrow),
                                label: Text(
                                    controller.isAnimating ? "WAIT ADS LOADING" : "WATCH AD"));
                          }),
                    ],
                  ),
                ),
              ],
            );
          }),
    );
  }
  void showRewardedAd() async {
    try {
      await videoAd.load(
    adUnitId: RewardedVideoAd.testAdUnitId,
    targetingInfo: targetingInfo);;

      await videoAd.show();
    } 
    catch(e){
      print(e);
    }
  }
}





class CustomTimerPainter extends CustomPainter {
  CustomTimerPainter({
    this.animation,
    this.backgroundColor,
    this.color,
  }) : super(repaint: animation);

  final Animation<double> animation;
  final Color backgroundColor, color;

  @override
  void paint(Canvas canvas, Size size) {
    Paint paint = Paint()
      ..color = backgroundColor
      ..strokeWidth = 10.0
      ..strokeCap = StrokeCap.butt
      ..style = PaintingStyle.stroke;

    canvas.drawCircle(size.center(Offset.zero), size.width / 2.0, paint);
    paint.color = color;
    double progress = (1.0 - animation.value) * 2 * math.pi;
    canvas.drawArc(Offset.zero & size, math.pi * 1.5, -progress, false, paint);
  }

  @override
  bool shouldRepaint(CustomTimerPainter old) {
    return animation.value != old.animation.value ||
        color != old.color ||
        backgroundColor != old.backgroundColor;
  }
}

Answer 1

我建议你尝试使用隔离。

您可能想查看这篇文章以获得完整的示例和解释：https://codingwithjoe.com/dart-fundamentals-isolates/