无法无条件访问属性“文档”，因为接收者可以为“空”[重复]

Question

当我使用这段代码时：

return FutureBuilder(
  future: searchResultsFuture,
  builder: (context, snapshot) {
    if (!snapshot.hasData) {
      return cargandoCircular();
    }

    List<UserResult> searchResults = [];
    snapshot.data.docs.forEach((doc) {
      User user = User.fromDocument(doc);
      UserResult searchResult = UserResult(user);
      searchResults.add(searchResult);
    });
 return ListView(
      children: searchResults,
    );

我得到错误：

The property 'docs' can't be unconditionally accessed because the receiver can be 'null'.
Try making the access conditional (using '?.') or adding a null check to the target ('!').

添加空检查并不能解决任何问题，而且所有内容都在另一个 dart 文件的 User 类中声明，如下所示：

class User {
final String id;
final String username;
final String email;
final String photoUrl;
final String displayName;
final String bio;

User(
  {required this.id,
  required this.username,
  required this.email,
  required this.photoUrl,
  required this.displayName,
  required this.bio});

factory User.fromDocument(DocumentSnapshot doc) {
return User(
  id: doc['id'],
  email: doc['email'],
  username: doc['username'],
  photoUrl: doc['photoUrl'],
  displayName: doc['displayName'],
  bio: doc['bio'],
);}}

Answer 1

使用这个访问它：

snapshot.data?.docs

因为快照中的数据可以为空，这就是为什么我们在未来的构建器中检查snapshot.hasData 是否为真。