flutter async

[phymo]

1. future （promise）

   Future<ProcessedData> createData(){
   return _loadFromDisk().then((id){
      return  _fetchNetworkData(id);
   }).catchError(
      (err)=> {
          print('error!')
   }).whenComplete(() {
          print('All done')
   });
   }

[phymo]

2. async/await

   Future<ProcessedData> createData() async{
   final id = await _loadFromDisk();
   final data = await _ fetchNetworkData(id);
   return data;
   }
   //can use try-catch to handle error

[phymo]

3. streamBuilder widget