Handling Dependency and Null Safety Issues in Flutter: A Complete Guide

When working with Flutter projects, you may encounter errors related to dependency versions and null safety, especially if you’re using an outdated or incompatible package. In this article, we’ll walk you through a common error and how to resolve it using the flutter pub outdated command.

The Issue

[holidaylandmark] flutter pub get --no-example
Resolving dependencies...
The current Dart SDK version is 3.3.3.

Because flutter_icons 1.1.0 doesn't support null safety and no versions of flutter_icons match >1.1.0 <2.0.0, flutter_icons ^1.1.0 is forbidden.
So, because holidaylandmark depends on flutter_icons ^1.1.0, version solving failed.

The lower bound of "sdk: '>=2.0.0-dev.68.0 <3.0.0'" must be 2.12.0 or higher to enable null safety.
For details, see https://dart.dev/null-safety
exit code 1

Let’s say you run the following command to get your Flutter dependencies:

flutter pub get --no-example

You might encounter an error that looks like this:

Resolving dependencies...
The current Dart SDK version is 3.3.3.

Because flutter_icons 1.1.0 doesn't support null safety and no versions of flutter_icons match >1.1.0 <2.0.0, flutter_icons ^1.1.0 is forbidden.
So, because holidaylandmark depends on flutter_icons ^1.1.0, version solving failed.

The lower bound of "sdk: '>=2.0.0-dev.68.0 <3.0.0'" must be 2.12.0 or higher to enable null safety.
For details, see https://dart.dev/null-safety
exit code 1

This error occurs because the package flutter_icons is not compatible with your current Dart SDK version (3.3.3) and does not support null safety, a feature introduced in Dart 2.12.0.

Understanding the Problem

• Null Safety: Ensures that no variable that hasn’t been initialized is accessed, reducing runtime errors.
• Dependency Version Incompatibility: Occurs when a package you’re using doesn’t support your Dart SDK’s version or lacks null safety support.

The Solution

To resolve this, you need to identify outdated packages and find compatible versions. Here’s how to do it:

1. Identify Outdated Packages: Run the following command to list outdated packages:

   flutter pub outdated

This will display a table showing the current, upgradable, resolvable, and latest versions of your dependencies.

2. Find Outdated Packages in Development Mode: Use this command to get more details, including pre-release versions:

   flutter pub outdated --mode=dev

This command helps you identify packages that need upgrading to support null safety or compatibility with the latest Dart SDK.

3. Update the Dependencies: Open your pubspec.yaml file and update the package version. For example:

   dependencies:
     flutter_icons: ^2.0.0

Make sure the version you’re updating to supports null safety and is compatible with your Dart SDK version.

4. Run flutter pub get: After updating your pubspec.yaml, run:

   flutter pub get

This should resolve the version conflict and update your dependencies successfully.

Additional Tips

• Always refer to the Dart null safety migration guide for understanding how null safety works.
• Regularly update your Flutter SDK and packages to avoid compatibility issues.

Conclusion

By following these steps, you can resolve dependency issues related to null safety and ensure that your Flutter projects run smoothly. This process is essential for keeping your project up-to-date, stable, and aligned with the latest Flutter and Dart improvements.