firebase DART中的FutureBuilder：“无法无条件调用方法”data“，因为接收方可以为”null“,请尝试进行调用...”

rryofs0p 于 2023-03-13 发布在其他

关注(0)|答案(2)|浏览(144)

这是几天了，现在我的工作Flutter代码通过以下教程，以学习如何使用Firebase与它。然而，我完全阻止了一个步骤，该人设法实现，但我复制了代码在100%，这里是我的错误：
The method 'data' can't be unconditionally invoked because the receiver can be 'null'. Try making the call conditional (using '?.') or adding a null check to the target ('!').
下面是代码：

class GetUserData extends StatelessWidget {
  final String documentId;
  final String fieldName;
  final String fieldTitle;

  GetUserData(
      {super.key,
      required this.documentId,
      required this.fieldName,
      required this.fieldTitle});

  @override
  Widget build(BuildContext context) {
    CollectionReference users = firestore.collection('Users');
    return FutureBuilder(
        future: users.doc(documentId).get(),
        builder:
            (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
            Map<String, dynamic> data = snapshot.data.data();
          return ListTile(
            title: Text(data[fieldName]),
            subtitle: Text(data[fieldTitle]),
          );
        });
  }
}

我试过很多方法：
Map<String, dynamic> data = snapshot.data!.data();
return FutureBuilder( future: users.doc(documentId).get(), builder: (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) { Map<String, dynamic> data = snapshot.data!.data() as Map<String, dynamic>; return ListTile( title: Text(data[fieldName]), subtitle: Text(data[fieldTitle]), ); });
在这里，当我使用_CastError (Null check operator used on a null value)进行调试时，我没有看到错误，而是崩溃
我到处都找遍了，我不知道该怎么解决这个问题，
非常感谢你的帮助

firebase

来源：https://stackoverflow.com/questions/75711866/futurebuilder-in-dart-the-method-data-cant-be-unconditionally-invoked-beca

2条答案

按热度按时间

eqqqjvef1#

您没有正确解码来自firebase的响应，请尝试考虑以下代码：

@override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
          child: FutureBuilder<DocumentSnapshot<Map<String, dynamic>>>(
        future: FirebaseFirestore.instance
            .collection('users')
            .doc(documentId) 
            .get(),
        builder: (_, snapshot) {
          if (snapshot.hasError) return Text('Error = ${snapshot.error}');
          if (snapshot.connectionState == ConnectionState.waiting) {
            return const Text("Loading");
          }
          Map<String, dynamic> data = snapshot.data!.data()!;
          return Text(data['fieldName']); // give your valid data here
        },
      )),
    );
  }

赞(0）回复(0）举报 2023-03-13

yrdbyhpb2#

设法处理所有情况

@override
  Widget build(BuildContext context) {
    CollectionReference users = firestore.collection('Users');
    return FutureBuilder(
        future: users.doc(documentId).get(),
        builder:
            (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
           /// success fetch data
          if(snapshot.hasData){
           Map<String, dynamic> data = jsonDecode(snapshot.data);
           return ListTile(
            title: Text(data[fieldName]),
            subtitle: Text(data[fieldTitle]),
          );
          }
         /// failed and throw error
          else if(snapshot.hasError){
            return Text('${snapshot.error}');
          } 
        /// loading condition
        else {
        return Center(child:CircularProggressIndicator());
         }
        });
  }

赞(0）回复(0）举报 2023-03-13

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firebase DART中的FutureBuilder：“无法无条件调用方法”data“，因为接收方可以为”null“,请尝试进行调用...”

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