How to enable Null-Safety in Flutter?

Question

I tried to use null safety, but it's giving me this error:

This requires the 'non-nullable' language feature to be enabled. Try updating your pubspec.yaml to set the minimum SDK constraint to 2.10.0 or higher, and running 'pub get'.

I changed my Dart SDK constraint from 2.7.0 to 2.10.0, but it's still showing this error.

Also, I upgraded my Dart and Flutter SDK:

dart-sdk v2.10.2 is the latest version available based on your source(s).

Flutter (Channel stable, 1.22.3, ...

Solution 1

To Enable null safety,

1. Check Latest Dart Version(It should be Dart 2.12 or later:)

   dart --version
   

2. Update the dart version, the above point not satisfied using the command.

   dart pub upgrade --null-safety
   
   dart pub get
   

3. Run the below command to know what are libs in your project needs to be upgraded to the latest null safety.

   dart pub outdated --mode=null-safety
   

The latest column shows the current version if it's in green that means dependency implemented null safety features if it red then the dependency owner needs to implement that.

4. Finally, run dart migration command which performs null safety migration on existing project(Existing project)

   dart migrate
   

5. If your package is ready to migrate, then the tool produces a line like the following:

   View the migration suggestions by visiting:

   http://127.0.0.1:60278/Users/you/project/mypkg.console-simple?authToken=Xfz0jvpyeMI%3D

Note: Even after running upgrade --null-safety command, you see the latest column section in red, which means a particular dependency hasn't supported null safety yet, so that means you cannot migrate the project.

for detail read: https://dart.dev/null-safety/migration-guide

Good blog on Implementation of Null Safety: https://medium.com/flutterworld/flutter-null-safety-5d20012c2441

Solution 2

Null safety is no longer an experiment as of Dart 2.12. It is now easy to enable.

Enabling null safety

Starting with the first Dart 2.12 versions, types will be non-nullable by default. So you just need to change your SDK constraint:

environment:
  sdk: ">=2.12.0 <3.0.0"

---

Learn more about "Enabling null safety" on dart.dev.

Solution 3

After Flutter 2.0.0 Stable u can run in app root folder:

dart migrate --apply-changes

Solution 4

This can happen when you upgrade the Flutter version you're using.

Try adding the following to the analysis_options.yml

analyzer:
    - enable-experiment:
        - non-nullable

Then, try cleaning and upgrading the project dependencies again.
To do that, you can use the following commands:

flutter clean
flutter packages pub upgrade
flutter pub run build_runner build

Finally, restart your IDE.

P.s. By the way, make sure that the sdk you're using is compatible with your Flutter version

Solution 5

Following the Dart documentation I was able to enable null safety in Flutter with these steps:

First add analysis_options.yaml:

analyzer:
  enable-experiment:
    - non-nullable

Then move to the dev channel and upgrade:

flutter channel dev
flutter upgrade

Change the sdk in pubspec.yaml

environment:
  sdk: ">=2.11.0-213.0.dev <2.12.0"

Clean the project:

flutter clean
flutter pub get

Restart the IDE (VS Code in my case).

And then it was working fine.

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Comments

[Abdallah El-Rashedy]

do I must to import something?

[Mirko Raimo]

Can you try restarting your ide? stackoverflow.com/a/62153557/10907417

[creativecreatorormaybenot]

@AbdallahEl-Rashedy This now does not require the enable-experiment anymore; see my answer.

[creativecreatorormaybenot]

Now, NNBD is no longer an experiment. See my answer.

[rgv]

" I'm not even going to try to find out why, I'm just going to get back to work!" I am taking this as a life lesson after trying to fix this issue :)

[Vinoth Vino]

It is now stable (Flutter 2.0.0)

[Kamlesh]

Getting error: [chatflutter] flutter pub get Running "flutter pub get" in chatflutter... The current Dart SDK version is 2.12.0-133.7.beta. Because chatflutter requires SDK version >=2.12.0 <3.0.0, version solving failed. pub get failed (1; Because chatflutter requires SDK version >=2.12.0 <3.0.0, version solving failed.) exit code 1

[creativecreatorormaybenot]

@Kamlesh Please make sure to run flutter upgrade :) Dart 2.12.0 is available as of Flutter 2.0.0.

[Kamlesh]

I have already developed the application and if I go with Dart 2.12 version with null safety feature then it will throw me back 10 days to solve all the issues are raised after applying Dart 2.12 version with null safety. BTW I have updated flutter version to 2.0.0 and made flutter ui changes in my app. I made a copy of my application and applied Dart 2.12 version then fixed Dart 2.12 updates related issues in my app and wasted 11-12 hours which was waste of time because many packages are not compatible with Dart 2.12 null safety feature, then I rolled back my application today. Thanks a lot.

[Kamlesh]

Dart is also saying that WAIT for the packages that you depend on to migrate, so not good to migrate to Dart 2.12 with null safety feature. dart.dev/null-safety/migration-guide

[Zamorite]

I think it's actually good to migrate as soon as you've got the green light, @Kamlesh . Like you said, you just have to wait for your dependencies before doing so. 🙃