Connectivity constructor
Connectivity()
Constructs a singleton instance of Connectivity.
Connectivity is designed to work as a singleton.
Implementation
// When a second instance is created, the first instance will not be able to listen to the
// EventChannel because it is overridden. Forcing the class to be a singleton class can prevent
// misuse of creating a second instance from a programmer.
factory Connectivity() {
_singleton ??= Connectivity._();
return _singleton!;
}