Flutter：空值animationController上使用的空检查运算符

mv1qrgav  于 2023-08-07  发布在  Flutter
关注(0)|答案(1)|浏览(163)

我是一个新的flutter开发者，而工作的flutter UI模板，我发现在网上，我遇到了这个错误，我似乎无法修复。
以下是错误：在构建Builder时抛出了以下_TypeError：用于空值的空检查运算符
导致错误的相关小部件为：MaterialApp MaterialApp：file：/C：/Users/Owner/Desktop/Dzidzo/Mobile%20application/dzidzo/lib/main.dart：21：18
当抛出异常时，这是堆栈：#0 _MyDiaryScreenState.initState（包：dzidzo/fitness_app/my_diary/my_diary_screenState.dart：30：47）#1 StatefulElement._firstBuild（包：flutter/src/widgets/framework.dart：5219：55）#2 ComponentElement.mount（包：flutter/src/widgets/framework.dart：5062：5）
下面是可能导致错误的代码：

class MyDiaryScreen extends StatefulWidget {
  const MyDiaryScreen({Key? key, this.animationController}) : super(key: key);

  final AnimationController? animationController;
  @override
  _MyDiaryScreenState createState() => _MyDiaryScreenState();
}

class _MyDiaryScreenState extends State<MyDiaryScreen>
    with TickerProviderStateMixin {
  Animation<double>? topBarAnimation;

  List<Widget> listViews = <Widget>[];
  final ScrollController scrollController = ScrollController();
  double topBarOpacity = 0.0;

  @override
  void initState() {
    topBarAnimation = Tween<double>(begin: 0.0, end: 1.0).animate(
        CurvedAnimation(
            parent: widget.animationController!,
            curve: Interval(0, 0.5, curve: Curves.fastOutSlowIn)));
    addAllListData();

    scrollController.addListener(() {
      if (scrollController.offset >= 24) {
        if (topBarOpacity != 1.0) {
          setState(() {
            topBarOpacity = 1.0;
          });
        }
      } else if (scrollController.offset <= 24 &&
          scrollController.offset >= 0) {
        if (topBarOpacity != scrollController.offset / 24) {
          setState(() {
            topBarOpacity = scrollController.offset / 24;
          });
        }
      } else if (scrollController.offset <= 0) {
        if (topBarOpacity != 0.0) {
          setState(() {
            topBarOpacity = 0.0;
          });
        }
      }
    });
    super.initState();
  }

  void addAllListData() {
    const int count = 9;

    listViews.add(
      TitleView(
        titleTxt: 'Mediterranean diet',
        subTxt: 'Details',
        animation: Tween<double>(begin: 0.0, end: 1.0).animate(CurvedAnimation(
            parent: widget.animationController!,
            curve:
                Interval((1 / count) * 0, 1.0, curve: Curves.fastOutSlowIn))),
        animationController: widget.animationController!,
      ),
    );
    listViews.add(
      MediterranesnDietView(
        animation: Tween<double>(begin: 0.0, end: 1.0).animate(CurvedAnimation(
            parent: widget.animationController!,
            curve:
                Interval((1 / count) * 1, 1.0, curve: Curves.fastOutSlowIn))),
        animationController: widget.animationController!,
      ),
    );
    listViews.add(
      TitleView(
        titleTxt: 'Meals today',
        subTxt: 'Customize',
        animation: Tween<double>(begin: 0.0, end: 1.0).animate(CurvedAnimation(
            parent: widget.animationController!,
            curve:
                Interval((1 / count) * 2, 1.0, curve: Curves.fastOutSlowIn))),
        animationController: widget.animationController!,
      ),
    );

    listViews.add(
      MealsListView(
        mainScreenAnimation: Tween<double>(begin: 0.0, end: 1.0).animate(
            CurvedAnimation(
                parent: widget.animationController!,
                curve: Interval((1 / count) * 3, 1.0,
                    curve: Curves.fastOutSlowIn))),
        mainScreenAnimationController: widget.animationController,
      ),
    );

    listViews.add(
      TitleView(
        titleTxt: 'Body measurement',
        subTxt: 'Today',
        animation: Tween<double>(begin: 0.0, end: 1.0).animate(CurvedAnimation(
            parent: widget.animationController!,
            curve:
                Interval((1 / count) * 4, 1.0, curve: Curves.fastOutSlowIn))),
        animationController: widget.animationController!,
      ),
    );

    listViews.add(
      BodyMeasurementView(
        animation: Tween<double>(begin: 0.0, end: 1.0).animate(CurvedAnimation(
            parent: widget.animationController!,
            curve:
                Interval((1 / count) * 5, 1.0, curve: Curves.fastOutSlowIn))),
        animationController: widget.animationController!,
      ),
    );
    listViews.add(
      TitleView(
        titleTxt: 'Water',
        subTxt: 'Aqua SmartBottle',
        animation: Tween<double>(begin: 0.0, end: 1.0).animate(CurvedAnimation(
            parent: widget.animationController!,
            curve:
                Interval((1 / count) * 6, 1.0, curve: Curves.fastOutSlowIn))),
        animationController: widget.animationController!,
      ),
    );

    listViews.add(
      WaterView(
        mainScreenAnimation: Tween<double>(begin: 0.0, end: 1.0).animate(
            CurvedAnimation(
                parent: widget.animationController!,
                curve: Interval((1 / count) * 7, 1.0,
                    curve: Curves.fastOutSlowIn))),
        mainScreenAnimationController: widget.animationController!,
      ),
    );
    listViews.add(
      GlassView(
          animation: Tween<double>(begin: 0.0, end: 1.0).animate(
              CurvedAnimation(
                  parent: widget.animationController!,
                  curve: Interval((1 / count) * 8, 1.0,
                      curve: Curves.fastOutSlowIn))),
          animationController: widget.animationController!),
    );
  }

  Future<bool> getData() async {
    await Future<dynamic>.delayed(const Duration(milliseconds: 50));
    return true;
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      color: FitnessAppTheme.background,
      child: Scaffold(
        backgroundColor: Colors.transparent,
        body: Stack(
          children: <Widget>[
            getMainListViewUI(),
            getAppBarUI(),
            SizedBox(
              height: MediaQuery.of(context).padding.bottom,
            )
          ],
        ),
      ),
    );
  }

  Widget getMainListViewUI() {
    return FutureBuilder<bool>(
      future: getData(),
      builder: (BuildContext context, AsyncSnapshot<bool> snapshot) {
        if (!snapshot.hasData) {
          return const SizedBox();
        } else {
          return ListView.builder(
            controller: scrollController,
            padding: EdgeInsets.only(
              top: AppBar().preferredSize.height +
                  MediaQuery.of(context).padding.top +
                  24,
              bottom: 62 + MediaQuery.of(context).padding.bottom,
            ),
            itemCount: listViews.length,
            scrollDirection: Axis.vertical,
            itemBuilder: (BuildContext context, int index) {
              widget.animationController?.forward();
              return listViews[index];
            },
          );
        }
      },
    );
  }

  Widget getAppBarUI() {
    return Column(
      children: <Widget>[
        AnimatedBuilder(
          animation: widget.animationController!,
          builder: (BuildContext context, Widget? child) {
            return FadeTransition(
              opacity: topBarAnimation!,
              child: Transform(
                transform: Matrix4.translationValues(
                    0.0, 30 * (1.0 - topBarAnimation!.value), 0.0),
                child: Container(
                  decoration: BoxDecoration(
                    color: FitnessAppTheme.white.withOpacity(topBarOpacity),
                    borderRadius: const BorderRadius.only(
                      bottomLeft: Radius.circular(32.0),
                    ),
                    boxShadow: <BoxShadow>[
                      BoxShadow(
                          color: FitnessAppTheme.grey
                              .withOpacity(0.4 * topBarOpacity),
                          offset: const Offset(1.1, 1.1),
                          blurRadius: 10.0),
                    ],
                  ),
                  child: Column(
                    children: <Widget>[
                      SizedBox(
                        height: MediaQuery.of(context).padding.top,
                      ),
                      Padding(
                        padding: EdgeInsets.only(
                            left: 16,
                            right: 16,
                            top: 16 - 8.0 * topBarOpacity,
                            bottom: 12 - 8.0 * topBarOpacity),
                        child: Row(
                          mainAxisAlignment: MainAxisAlignment.center,
                          children: <Widget>[
                            Expanded(
                              child: Padding(
                                padding: const EdgeInsets.all(8.0),
                                child: Text(
                                  'My Diary',
                                  textAlign: TextAlign.left,
                                  style: TextStyle(
                                    fontFamily: FitnessAppTheme.fontName,
                                    fontWeight: FontWeight.w700,
                                    fontSize: 22 + 6 - 6 * topBarOpacity,
                                    letterSpacing: 1.2,
                                    color: FitnessAppTheme.darkerText,
                                  ),
                                ),
                              ),
                            ),
                            SizedBox(
                              height: 38,
                              width: 38,
                              child: InkWell(
                                highlightColor: Colors.transparent,
                                borderRadius: const BorderRadius.all(
                                    Radius.circular(32.0)),
                                onTap: () {},
                                child: Center(
                                  child: Icon(
                                    Icons.keyboard_arrow_left,
                                    color: FitnessAppTheme.grey,
                                  ),
                                ),
                              ),
                            ),
                            Padding(
                              padding: const EdgeInsets.only(
                                left: 8,
                                right: 8,
                              ),
                              child: Row(
                                children: <Widget>[
                                  Padding(
                                    padding: const EdgeInsets.only(right: 8),
                                    child: Icon(
                                      Icons.calendar_today,
                                      color: FitnessAppTheme.grey,
                                      size: 18,
                                    ),
                                  ),
                                  Text(
                                    '15 May',
                                    textAlign: TextAlign.left,
                                    style: TextStyle(
                                      fontFamily: FitnessAppTheme.fontName,
                                      fontWeight: FontWeight.normal,
                                      fontSize: 18,
                                      letterSpacing: -0.2,
                                      color: FitnessAppTheme.darkerText,
                                    ),
                                  ),
                                ],
                              ),
                            ),
                            SizedBox(
                              height: 38,
                              width: 38,
                              child: InkWell(
                                highlightColor: Colors.transparent,
                                borderRadius: const BorderRadius.all(
                                    Radius.circular(32.0)),
                                onTap: () {},
                                child: Center(
                                  child: Icon(
                                    Icons.keyboard_arrow_right,
                                    color: FitnessAppTheme.grey,
                                  ),
                                ),
                              ),
                            ),
                          ],
                        ),
                      )
                    ],
                  ),
                ),
              ),
            );
          },
        )
      ],
    );
  }
}

字符串
我在网上尝试了很多解决方案，说了一些关于替换空操作符的东西！”但我似乎不能让它工作

flutter

1条答案

按热度按时间
kmynzznz

kmynzznz1#

您遇到的错误是由于使用了null检查运算符（！）的可空值widget.animationController。
您的MyDiaryScreen小部件依赖于AnimationController，该小部件当前为空。要解决这个问题，请将animationController参数设为不可空，并且在将其作为参数传递时是必需的。这样，您就不需要使用空校验运算符（！）在整个widget代码中。

class MyDiaryScreen extends StatefulWidget {
  const MyDiaryScreen({Key? key, required this.animationController})
      : super(key: key);

  final AnimationController animationController;

  @override
  _MyDiaryScreenState createState() => _MyDiaryScreenState();
}

字符串
每次使用MyDiaryScreen小部件时，请确保提供必要的animationController。

或者

考虑是否有必要提供动画控制器作为参数。如果可以在MyDiaryScreen中创建新的动画控制器，则可以进行以下更改：

class MyDiaryScreen extends StatefulWidget {
  const MyDiaryScreen({Key? key}) : super(key: key);

  @override
  _MyDiaryScreenState createState() => _MyDiaryScreenState();
}

class _MyDiaryScreenState extends State<MyDiaryScreen>
    with TickerProviderStateMixin {
  late AnimationController animationController;

  @override
  void initState() {
    animationController = AnimationController(
      vsync: this,
      duration: const Duration(milliseconds: 500),
    );
    // rest of your initState code...
  }
  // rest of your _MyDiaryScreenState class...
}

型
这样，您就可以在MyDiaryScreen小部件中创建一个新的AnimationController，从而避免了外部初始化的需要。

赞(0）分享  回复(0）举报  2023-08-07
我来回答

相关问题

    查看更多

    热门标签

    更多
    JavaquerypythonNode开发语言requestUtil数据库Table后端算法LoggerMessageElementParser

    最新问答

    更多
    • 蜀ICP备13028337号-1 大数据知识库 https://www.saoniuhuo.com © All rights reserved
    • 本站内容来源互联网,如果侵犯您的权益请联系我们删除, 联系方式：448109455@qq.com