flutter-方法[]在空时被调用

Question

我一直在学习如何构建一个类似Instagram的社交媒体应用程序的教程，尽管我的代码与教程中的代码相同，但当我试图显示用户的帖子时，我得到了这个错误：

building FutureBuilder（脏，状态:_FutureBuilderState#0C840)引发了以下NosuchMethodeRor:方法“[]”是在NULL上调用的。接收者：null尝试调用：

  @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,
                ),
              ],
            ),
          ),
        );
      },
    );
  }

  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null

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