LateInitializationError: Field 'user' has not been initialized

Question

我对用户初始值有疑问。

我有这种类型的源代码：“https:// paste.ofcode.org/ycHT4YFsDGSQXa68JiKJRH”

链接中的重要行：

  child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                Container(
                  height: 240,
                  child: FutureBuilder(
                      future: getCurrentUser(),
                      builder: (context, snapshot) {
                        return ListView.separated(
                          itemBuilder: (context, index) {
                            print(index);
                            return GetUserName(documentId: user?.uid);
                          },
                          separatorBuilder: (context, index) {
                            return SizedBox(width: 10);
                          },
                          itemCount: myCards.length,
                          shrinkWrap: true,
                          scrollDirection: Axis.horizontal,
                        );
                      }),

我也有这个class，

class GetUserName extends StatelessWidget {
  final String documentId;
  final int index = 0;

  GetUserName({
    required this.documentId,
  });

  @override
  Widget build(BuildContext context) {
    // get the collection
    CollectionReference users = FirebaseFirestore.instance.collection('Users');

    return FutureBuilder<DocumentSnapshot>(
      future: users.doc(documentId).get(),
      builder: (context, snapshot) {
        if (snapshot.connectionState == ConnectionState.done) {
          Map<String, dynamic> data =
              snapshot.data!.data() as Map<String, dynamic>;
          return MyCard(
            userName: data['username'],
            card: myCards[index],
          );
          //  Text('First Name: ${data['username']}');

        } else {
          print("here");
          return MyCard(
            userName: "Waiting",
            card: myCards[index],
          );
        }
        return Text('loading..');
      },
    );
  }
}

我在 90th 行中使用 FutureBuilder，它的未来值是 getCurrentUser() 这个函数创建这个值 user = await _auth.currentUser;

然后我在第 96 行的 GetUserName 函数中给了 user?.uid 参数（目的：将当前用户 ID 给 GetUserName）。

我在 MyCard 中成功看到当前用户名，但我也有错误

======== Exception caught by widgets library =======================================================
The following LateError was thrown building:
LateInitializationError: Field 'user' has not been initialized.

我该如何解决这个问题？

Answer 1

使用 User? user 而不是 late final user 以便能够在加载用户之前检查空值。在获取用户时的 getCurrentUser() 方法中，使用 setState 更新用户和当前状态：

Future getCurrentUser() async {
  final loadedUser = await _auth.currentUser;

    if (loadedUser != null) {
      setState(() {
        user = loadedUser;
      });
    }
}

LateInitializationError: Field 'user' has not been initialized

LateInitializationError: Field 'user' has not been initialized

flutter