Flutter-方法[]在null上被调用

Question

我一直在关注如何构建类似于 Instagram 的社交媒体应用程序的教程，虽然我的代码与教程中的代码相同，但在尝试显示用户的帖子时出现此错误：

以下 NoSuchMethodError 被抛出构建 FutureBuilder(dirty, state: _FutureBuilderState#0c840): 方法 '[]' 在 null 上被调用。接收者：null 尝试调用：

相关的导致错误的小部件是：FutureBuilder file:///Users/Michael/Desktop/Flutter%20Projects/greenroom/lib/pages/PostScreenPage.dart:19:12 抛出异常时，这是堆栈：#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5) #1 文档快照。[] （包：cloud_firestore/src/document_snapshot.dart:29:42）#2 新 Post.fromDocument（包：buddiesgram/widgets/PostWidget.dart:36:31） #3 PostScreenPage.build。 （包：buddiesgram/pages/PostScreenPage.dart:26:26）#4 _FutureBuilderState.build (package:flutter/src/widgets/async.dart:751:55)

这是 FutureBuilder：

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: postsReference.document(userId).collection("usersPosts").document(postId).get(),
      builder: (context, dataSnapshot){
        if(!dataSnapshot.hasData){
          return circularProgress();
        }

        Post post = Post.fromDocument(dataSnapshot.data);
        return Center(
          child: Scaffold(
            appBar: header(context, strTitle: post.description),
            body: ListView(
              children: <Widget>[
                Container(
                  child: post,
                ),
              ],
            ),
          ),
        );
      },
    );
  }

这是帖子：

  factory Post.fromDocument(DocumentSnapshot documentSnapshot){
    return Post(
      postId: documentSnapshot["postId"],
      ownerId: documentSnapshot["ownerId"],
      //postId: documentSnapshot["timestamp"],
      likes: documentSnapshot["likes"],
      username: documentSnapshot["username"],
      description: documentSnapshot["description"],
      location: documentSnapshot["location"],
      url: documentSnapshot["url"],
    );
  }

Answer 1

尝试检查该值是否为空

if(dataSnapshot.data == null || !dataSnapshot.hasData){
  return circularProgress();
}