This error occurred while updating from flutter 1.0 to 2.0-CodePudding

The syntax seems to have changed with the update of flutter. I tried to find a solution on the official site, but failed.


import 'package:flutter/material.dart';
import 'package:my_app1/model/model_member.dart';

class MainScreen extends StatefulWidget {
  final Member member;
  DetailScreen({this.member});
  _DetailScreenState createState() => _DetailScreenState();
}

Error: The parameter 'member' can't have a value of 'null' because of its type 'Member', but the implicit default value is 'null'.

and also

  Widget _buildBody(BuildContext context) {
    return StreamBuilder<QuerySnapshot>(
      stream: FirebaseFirestore.instance.collection('member').snapshots(),
      builder: (context, snapshot) {
        if (!snapshot.hasData) return LinearProgressIndicator();
        return _buildList(context, snapshot.data.docs);
      },
    );
  }

Error: Property 'docs' cannot be accessed on 'QuerySnapshot<Object?>?' because it is potentially null.

CodePudding user response：

Try this:

StreamBuilder<QuerySnapshot>(
              stream: FirebaseFirestore.instance
                  .collection("member")
                  .snapshots(),
              builder: (BuildContext context,
                  AsyncSnapshot<QuerySnapshot> chatSnapshot) {
                if (chatSnapshot.connectionState == ConnectionState.waiting) {
                  return Center(
                    child: Container(),
                  );
                }
                return ListView(
                  reverse: true,
                  controller: _controller,
                  physics: const BouncingScrollPhysics(),
                  children:
                      chatSnapshot.data!.docs.map((DocumentSnapshot document) {
                    Map<String, dynamic> data =
                        document.data()! as Map<String, dynamic>;
                      return Text(data["name"]);
                  }).toList(),
                );
              },
            ),

CodePudding user response：

The main change from flutter 1.0 to 2.0 is Null safety. So it will make sure that the member field is not null. so adding required in front of the member should fix the problem

class MainScreen extends StatefulWidget {
  final Member member;
  DetailScreen({required this.member}); // <-- change this line
  _DetailScreenState createState() => _DetailScreenState();
}