Question

我使用Firebase作为后端开发Flutter应用程序，当我从屏幕移到另一个BottomNavigationBar时，我正在使用StreamProvider将配置文件数据传递到另一个屏幕。

当我移到另一个屏幕时，我收到此错误：

 The getter 'length' was called on null.
Receiver: null
Tried calling: length

The relevant error-causing widget was: 
  ProfileList

这是ProfileList和ProfileTile

class ProfileList extends StatefulWidget {
  @override
  _ProfileListState createState() => _ProfileListState();
}

class _ProfileListState extends State<ProfileList> {
  @override
  Widget build(BuildContext context) {

final profiles = Provider.of<List<Profile>>(context);

return ListView.builder(
    itemCount: profiles.length,
    itemBuilder: (context, index){
      return ProfileTile(profile: profiles[index]);
});
  }
}

ProfileTile

class ProfileTile extends StatefulWidget {
  final Profile profile;
  ProfileTile({this.profile});
  @override
  _ProfileTileState createState() => _ProfileTileState();
}

class _ProfileTileState extends State<ProfileTile> {



  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: EdgeInsets.only(top: 8),
      child: Card(
        margin: EdgeInsets.fromLTRB(20, 6, 20, 0),
        child: ListTile(
          leading: CircleAvatar(
            radius: 25,
            backgroundColor: Colors.green,
          ),
          title: Text(widget.profile.userName),
          subtitle: Text(widget.profile.city),
        ),
      ),
    );
  }
}

Answer 1

看来，

itemCount：profiles.length，

部分在提供程序向其发送数据之前呈现。因此配置文件变量为null。

尝试一下

itemCount: (profiles == null) ? 0 : profile.length,

Flutter / Firebase在null上调用了getter'length'

1 个答案: