existsOnPrefs method
Checks if the key exists in SharedPreferences.
Returns true if the key exists, even if its value is null.
Example:
final username = PrfString('username');
if (await username.existsOnPrefs()) {
// The key exists in storage
}
Implementation
Future<bool> existsOnPrefs() async {
final prefs = await Prf.getInstance();
return prefs.containsKey(key);
}