如何在 null 安全后将您的 Flutter 项目（应用程序）升级到最新的 Flutter 版本？

Question

I want to upgrade my project which is on Flutter 2.0 to the latest version of flutter (2.5).

I have already seen this question which is most relevant. How do I upgrade an existing Flutter app?

In my Mac, I have Flutter upgraded to 2.5. You can see the output of flutter doctor -v below:

[✓] Flutter (Channel stable, 2.5.0, on macOS 11.5.2 20G95 darwin-arm, locale
    en-PK)
    • Flutter version 2.5.0 at /Users/ahmad/development/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 4cc385b4b8 (9 days ago), 2021-09-07 23:01:49 -0700
    • Engine revision f0826da7ef
    • Dart version 2.14.0

[✓] Android toolchain - develop for Android devices (Android SDK version 31.0.0)
    • Android SDK at /Users/ahmad/Library/Android/sdk
    • Platform android-31, build-tools 31.0.0
    • Java binary at: /Applications/Android
      Studio.app/Contents/jre/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 12.5.1, Build version 12E507
    • CocoaPods version 1.11.0

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2020.3)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)

[✓] Connected device (2 available)
    • iPhone 12 Pro Max (mobile) • 57868E1C-4871-4185-A797-383121736AB8 • ios
      • com.apple.CoreSimulator.SimRuntime.iOS-14-5 (simulator)
    • Chrome (web)               • chrome                               •
      web-javascript • Google Chrome 93.0.4577.82

• No issues found!

I have searched over the internet about it. Mostly, I see two things, either how to upgrade to null-safety (which means from earlier versions to 2.0) or how to upgrade Flutter sdk in your system.

I have tried running flutter upgrade command which says I'm up-to-date. I have also tried running flutter pub upgrade . Both do not change the version of flutter in the pubspec.lock file inside my project which says at the end of file:

sdks:
  dart: ">=2.14.0 <3.0.0"
  flutter: ">=2.0.0"

Please guide me how can I upgrade my project to the latest version. Thanks in advance :)

Answer 1

You're using flutter: >=2.0.0 which basically tells your app to use 2.0.0. Usually using the flutter sdk constraint is only used in plugins. It's okay to leave this out, if you remove flutter: >=2.0.0 it will automatically use your SDK version

Answer 2

The Flutter project will have the same version as your system does. If you have the latest Flutter version on your system, then the app built from that system will have the latest version.

For example, if your system has Flutter 2.8 (latest while answering) and you build an app through it, your app is based on 2.8.