Turn off Null Safety for previous Flutter Project?

Question

I want to upgrade my flutter to get new features such as null safety, but I didn't want my previous project to affect them. I want new changes only for my new flutter project, I want to run my old project similar to the old way. Is there any way? Please guide me through it.

Thank You

Answer 1

Setting SDK constraints in your old project's pubspec.yaml file should be enough.

For example, the following, does not have null safety enabled:

environment:
  sdk: ">=2.11.0 <3.0.0"

You can also specify at the top of your Dart file to disable null checks for that file.

// @dart=2.9

Answer 2

The above answer wasn't working for me after I upgraded to Dart v2.12 on the beta channel. So I found these options:

You can add this to the top of any dart file to disable null-safety checks.

// @dart=2.9

or similar to the answer above, I had to include a version prior to 2.12 to disable null safety. You would edit this line in the pubspec.yaml file.

environment:
  sdk: ">=2.11.0 <3.0.0"

Answer 3

You can run flutter project without null safety with --no-sound-null-safety option with flutter run.

Also you can add this as an argument in launch.json in VSCode

"configurations": [
        {
            "name": "Flutter",
            "request": "launch",
            "type": "dart",
            "flutterMode": "debug",
            "args": [
                "--no-sound-null-safety"
            ],
        },
]