方法[]不能无条件调用，因为接收者可以是null

Question

I'm trying to follow along this 2 year old Fluter tutorial on Udemy its based on a ride sharing app, but I've come to a halt. am receiving this error

The method '[]' can't be unconditionally invoked because the receiver can be 'null'

I don't really know how to go around it. I'm supposed to retrieve some user info stored on Firebase Realtime Database like the Username to be easily accessible in all the apps pages, but android studio is giving me errors when making this model. I've tried adding the null checks like below, seems not to work

Null(!) checks apllied

User.fromSnapshot(DataSnapshot snapshot){

 id = snapshot.key; phone = snapshot.value;['phone']. email = snapshot;value.['email']; fullName = snapshot.value!['fullname'];

}

I'm not quiet sure if there is a mistake on the constructor!

Code for the user datamodel

import 'package:firebase_database/firebase_database.dart';

class User{
  var fullName;
  var email;
  var phone;
  var id;

  User({
    this.email,
    this.fullName,
    this.phone,
    this.id,
  });

  User.fromSnapshot(DataSnapshot snapshot){

    id = snapshot.key;
    phone = snapshot.value['phone'];
    email = snapshot.value['email'];
    fullName = snapshot.value['fullname'];
  }
}

Answer 1

thats null-safety in flutter.

there 2 option:

• make value nullable

class User{
  final String? fullName;
  final String? email;
  final String? phone;
  final int? id;

  User({
    this.email,
    this.fullName,
    this.phone,
    this.id,
  });

with this, your variable in user can be null, if no data from snapshoot

• make it non-null

class User{
  final String fullName;
  final String email;
  final String phone;
  final int id;

  User({
    required this.email,
    required this.fullName,
    required this.phone,
    required this.id,
  });
// since its required, it cant be null. 
// if snapshot value is null, it will error.
// we can assign another default value

User.fromSnapshot(DataSnapshot snapshot){

    id = snapshot.key ?? -1;
    // if phone is null, its set to empty string
    phone = snapshot.value['phone'] ?? ''; 
    email = snapshot.value['email'] ?? '';
    fullName = snapshot.value['fullname'] ?? ''; 
  }

Answer 2

Try the following code:

import 'package:firebase_database/firebase_database.dart';

class User{
  var fullName;
  var email;
  var phone;
  var id;

  User({
    this.email,
    this.fullName,
    this.phone,
    this.id,
  });

  User.fromSnapshot(DataSnapshot snapshot){

    id = snapshot.key;
    phone = snapshot.value['phone']!;
    email = snapshot.value['email']!;
    fullName = snapshot.value['fullname']!;
  }
}

or

import 'package:firebase_database/firebase_database.dart';

class User{
  var fullName;
  var email;
  var phone;
  var id;

  User({
    this.email,
    this.fullName,
    this.phone,
    this.id,
  });

  User.fromSnapshot(DataSnapshot snapshot){

    id = snapshot.key;
    phone = snapshot.value['phone'] ?? 'phone';
    email = snapshot.value['email'] ?? 'email';
    fullName = snapshot.value['fullname'] ?? 'fullname';
  }
}