start method
Implementation
@override
Future<bool> start({bool refresh = false, String? key}) async {
bool ok = true;
if (mqtt == null && url != null) {
mqtt = IMqtt.create(url!, this, username: username, password: password);
}
if (mqtt != null) {
ok = await mqtt!.connect();
connected = ok;
} else {
connected = false;
ok = false;
}
return ok;
}