This is an example of FLutter application that fetches the London's weather data from a public API. It is build using the reactive programming and is structured under the BLoC pattern. You can find all step-by-step implementation details in a Medium article designed to prove the reactive programming and the BLoC pattern concepts in Flutter.
You can add improvments to the app in terms of UI, but much more you can use Dependency Injection to avoid thight coupling between classes. For this purpose, another Medium article is available for you. Please read it for more details.