singleton.dart

void main() {
var state =  AppState.instance;
  
  print(state.appName);
}
class AppState {
  String appName;
  AppState._internal(){
    
    appName="FaceBook";
  }
  static AppState _instance;
  
  static  AppState get instance  {
    
    if(_instance == null) {
      _instance=  AppState._internal();
;
      
    }
    return _instance;
  }
  
  
  
}