flutter 方法称为 null

Question

I am trying to display a badge to show my uses that they have an unread message but I keep getting this error The method '[]' was called on null. Receiver: null Tried calling: []("recieverId") The relevant error-causing widget The method '[]' was called on null. Receiver: null Tried calling: []("recieverId") The relevant error-causing widget

here is my code

   class ViewLayout extends StatelessWidget {
  final User contact;
  final ChatMethods _chatMethods = ChatMethods();

  ViewLayout({
    @required this.contact,
  });

  bool isread;
  Map<dynamic, dynamic> chatlist;
  @override
  Widget build(BuildContext context) {
    final UserProvider userProvider = Provider.of<UserProvider>(context);
    FirebaseUser user;
    if (chatlist['recieverId'] == user.uid) {
      isread = true;
    } else {
      isread = chatlist['isread'] == null ? true : chatlist['isread'];
    }

convo class

    class Convo {
  Convo({this.chatlist});

  factory Convo.fromFireStore(DocumentSnapshot doc) {
    final Map<String, dynamic> data = doc.data;

    return Convo(chatlist: data['chatlist'] ?? <dynamic>{});
  }

  Map<dynamic, dynamic> chatlist;
}

Answer 1

Add null check before using chatlist, because your chatlist is null.

if(chatlist !=null){
    if (chatlist['recieverId'] == user.uid) {
          isread = true;
        } else {
          isread = chatlist['isread'] == null ? true : chatlist['isread'];
        }
}