dart_future.dart

dart_future.dart

import 'dart:async';

main() async {
  //final version = -1;
  //final version = 0;
  final version = 1;
  
  // use then / catchError
  print('handle with then-catchError');
  checkVersion(version)
      .then((o) {
        print('future done');
      })
      .catchError((e) => print('future format error $e'),
          test: (e) => e is FormatException)
      .catchError((e) {
        print('future $e');
      })
      .whenComplete(() => print('future complete'));
  
  // use try catch
  print('\nhandle with try-catch');
  try {
    await checkVersion(version);
    print('try-catch done');
  } on FormatException catch (e) { 
    print('try-catch format error $e');
  } catch (e) {
    print('try-catch error $e');
  } finally {
    print('try-catch finally');
  }
  
  print(await someFutureResult());
  print('Exit');
}

Future checkVersion(int value) async {
  await Future.delayed(Duration(seconds: 1));
  if (value == 0) {
    throw 'error';
  } else if (value == -1) {
    throw FormatException();
  }
  return value;
}


/// Sometimes we need to have Completer for async operation
Future<dynamic> someFutureResult(){
   final c = new Completer();
   // complete will be called in 3 seconds by the timer.
   Timer(Duration(seconds: 3), () {     
       print("Yeah, this line is printed after 3 seconds");
       c.complete("you should see me final");       
   });
   return c.future;
}