在我实施了 Getx 状态管理后，“在 null 上调用了 getter 'visible'。”答案

【问题标题】：After I have implemented Getx state management "The getter 'visible' was called on null."在我实施了 Getx 状态管理后，“在 null 上调用了 getter 'visible'。”
【发布时间】：2020-08-10 12:43:51
【问题描述】：

我刚开始学习dart/flutter，非常喜欢flutter框架，但是当我开始玩一些状态管理时遇到了问题，我选择了Getx。在我将state management 集成到我的项目中之后......我开始遇到这个问题


════════ Exception caught by scheduler library ═════════════════════════════════
The getter 'visible' was called on null.
Receiver: null
Tried calling: visible
════════════════════════════════════════════════════════════════════════════════
Another exception was thrown: NoSuchMethodError: The getter 'visible' was called on null.

对我来说已经很难调试了。如果这里的任何人都可以说明我该如何解决这个错误......会很棒。

我的模型

class TransactionModel {
  List<Data> data;

  TransactionModel({
    this.data,
  });

  factory TransactionModel.fromJson(List<dynamic> parsedJson) {
    List<Data> transactions = new List<Data>();
    transactions = parsedJson.map((i) => Data.fromJson(i)).toList();
    return TransactionModel(
      data: transactions ?? transactions,
    );
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (this.data != null) {
      data['data'] = this.data.map((v) => v.toJson()).toList();
    }
    return data;
  }
}

class Data {
  String id;
  String title;
  double amount;
  String created;
  String fileUrl;

  Data({
    this.id,
    this.title,
    this.amount,
    this.created,
    this.fileUrl,
  });

  Data.fromJson(Map<String, dynamic> json) {
    id = json['id'].toString() ?? json['id'].toString();
    title = json['title'] ?? json['title'];
    amount = json['amount'] ?? json['amount'];
    created = json['created'] ?? json['created'];
    fileUrl = json['fileUrl'] ?? json['fileUrl'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();

    data['id'] = this.id ?? this.id;
    data['title'] = this.title ?? this.title;
    data['amount'] = this.amount ?? this.amount;
    data['created'] = this.created ?? this.created;
    data['fileUrl'] = this.fileUrl ?? this.fileUrl;

    return data;
  }
}

我的控制器

class TransactionController extends GetxController {
  var trasanctionListData = List<Data>().obs;
  @override
  void onInit() {
    _getTransactionList();
    super.onInit();
  }

  void _getTransactionList() async {
    Future.delayed(
      Duration.zero,
      () => Get.dialog(
        Center(
          child: CircularProgressIndicator(),
        ),
        barrierDismissible: false,
      ),
    );

    Request request = Request(url: 'transactions', body: null);
    request.get().then((value) {
      TransactionModel transactionModel = TransactionModel.fromJson(
        json.decode(value.body),
      );
      trasanctionListData.value = transactionModel.data;
    }).catchError((onError) {
      Get.rawSnackbar(
        title: 'Error',
        message: '${onError.message}',
        icon: Icon(
          Icons.error,
          color: AppColors.greyishBrown,
        ),
      );
    });
  }
}

我的看法

class TransactionView extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final TransactionController _controller =
        Get.put<TransactionController>(TransactionController());
    return Scaffold(
      backgroundColor: AppColors.cloudyWhite,
      appBar: MiAppBar(title: 'Overview'),
      body: SingleChildScrollView(
        child: Column(
          children: [
            Carousel(),
            Obx(
              () => ListView.builder(
                itemCount: _controller.trasanctionListData.length,
                itemBuilder: (context, index) => TransactionItem(
                  key: ValueKey(_controller.trasanctionListData[index].id),
                  title: _controller.trasanctionListData[index].title,
                  amount: _controller.trasanctionListData[index].amount,
                  createdAt: _controller.trasanctionListData[index].created,
                  deleteOnClick: () {},
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

【问题讨论】：

标签： flutter dart state-management

【解决方案1】：

经过调试并注意错误信息，我发现我的案例的问题是； listView 正在寻找父级的高度，在我的情况下，父级是 Obx 小部件，然后列和那些小部件没有定义的高度，我通过用容器小部件包装 Obx 小部件来解决我的问题，并为 Container 小部件指定高度。我不知道是否是正确的解决方案，但对我来说工作。

【讨论】：