Use case

As per the current implementation, the shared_preferences plugin allows setting a custom prefix using setPrefix before any instances are instantiated. However, if setPrefix is called after getInstance, it results in a failure, even if the new prefix matches the previously set one. This poses challenges in complex applications where multiple independent packages might attempt to set or check the prefix independently, leading to potential conflicts and runtime exceptions.

Proposal

1. Introduce a hasInstance() method: This method would allow developers to check if an instance of SharedPreferences has already been created, which helps in deciding whether it’s safe to call setPrefix.
2. Modify setPrefix() to allow idempotent operations: If setPrefix is called with a prefix that matches the already set prefix, the method should not fail. This adjustment would make the prefix setting idempotent and safer in environments where multiple checks might occur.