库“package:flutter/material.dart”是遗留的，不应导入到 null 安全库中

Question

I have a null-safe library and in the example folder I'm using the following import:

import 'package:flutter/material.dart';

However, the linter is giving me the following warning:

The library 'package:flutter/material.dart' is legacy, and should not be imported into a null safe library. Try migrating the imported library. import_of_legacy_library_into_null_safe

The example project's pubspec.yaml file specifies the beta version of the Dart SDK:

environment:
  sdk: ">=2.12.0-29.10.beta <3.0.0"

dependencies:
  flutter:
    sdk: flutter
  my_library:
    path: ../

Hasn't material.dart already been converted by now? Do I need to add something else to pubspec.yaml or just wait for the stable release to come out?

Answer 1

Use dart pub outdated --mode=null-safety and then dart pub upgrade --null-safety to upgrade all your dependencies to null-safety.

For more details go to https://dart.dev/null-safety/migration-guide .

Answer 2

The fix for this is relatively simple. Just go to your pubspec.yaml file and make sure the lottie dependancy that you have there, is the latest version as on the pub.dev site.

Answer 3

Currently, on 8/29/2021, a uto_size_text package also keeps giving this alert , because I was using the Null Safety versions of Dart - 2.12.0, and to solve this, I looked in the package documentation and saw that I had a Prerelease version to Null Safety - launch, so I used it.

dependencies:
  auto_size_text: ^3.0.0-nullsafety.0

Answer 4

[:[The library 'package:flutter_ / .dart' is legacy, and should not be imported into a null safe library. Try migrating the imported library.

Open run/debug option -> select edit configuration as shown in image one.] 1 ] 1

.imgur.com/A9aEb.png

Answer 5

I was facing the same problem with the Adhan Dart package, when i read the documentation on the package site, i had the Prereleased version so i made changes to the dependences as adhan: ^2.0.0-nullsafety.2 and it worked.

For more details: https://pub.dev/packages/adhan/versions/2.0.0-nullsafety.1

Answer 6

In case someone comes here looking for this error because of the flutter realm package. Please change your realm version in your pubspec.yaml file to a version with null safety. Check out the latest realm versions from https://pub.dev/packages/realm/versions .

Change From

dependencies
  realm: ^0.0.1

To

dependencies
   realm: ^0.8.0+rc  //check for latest version

Answer 7

go to https://pub.dev/packages/font_awesome_flutter ,

copy the latest release version of font ie in my case (font_awesome_flutter: ^9.1.0),

then add it to your pubspec.yaml file ie (font_awesome_flutter: ^9.1.0),

click pub get dependencies

go to your input_page file

click get dependencies

Answer 8

Copy the latest version of the package which is giving the error from http://pub.dev/ and paste it in the pubspec.yaml file.

Answer 9

In my case I got this error because I defined 'firebase_core' dependency in the pubspec.yaml file under the 'dev_dependencies' but it was wrong.

I've done 3 easy steps to solve the issue as following:

1- I've got the latest version from https://pub.dev/packages website.

2- I've defined the packages under 'dependencies' in the pubspec.yaml file as following:

dependencies:
  flutter:
    sdk: flutter
  firebase_core: ^2.3.0

3- I've imported the package in the main.dart file as following:

import 'package:firebase_core/firebase_core.dart';

Future main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

Answer 10

in my case my firebase_core package was not of the latest version. do check yours or any other firebase related dependencies. some packages maybe old version.

Answer 11

If you want to use null safety, either wait for the stable release so that all of the dependencies can support the null safety.
Or you can use the null safety by switching to the beta channel of the Flutter SDK.

Use the following command to switch to the flutter beta channel.

$ flutter channel beta
$ flutter upgrade

Be careful if you are working on production code because this may break something in the code. If you are working on production then stick to the flutter stable channel.

You can check the dependency status using the following command:

$ dart pub outdated --mode=null-safety