Flutter03 dart asynchronous

Future

Dart Is a single thread programming language

• Future Object encapsulates Dart Asynchronous operation of , It has unfinished （uncompleted） And completed （completed） Two kinds of state .
• completed There are two states ： One is the success of the operation , Return results ; The other is the failure of the operation , Returns an error .

1.1 then

void main(List<String> arguments) {
    
  print('start');
  Future f = getNetwort();
  print(f.then((value) => print(value)).catchError((onError){
    
    print(onError);
  }));
  print('end');
}


Future<String> getNetwort(){
    
  return Future((){
    
    sleep(Duration(seconds: 2));
    // throw Exception('403');
    return "yh";
  });
}

//start
//Instance of 'Future<void>'
//end
//yh
//Exception: 403

1.2 async and await