Delete all the packages folders in your project (also in subfolders). Delete the pubspec. lock file in your project. Run pub get again from a command line or select Tools in the Dart Editor menu, and then select Pub Get.
Delete all the packages folders in your project (also in subfolders). Delete the pubspec. lock file in your project. Run pub get again from a command line or select Tools in the Dart Editor menu, and then select Pub Get.