I have a custom class that fetches data from the database, that returns Future<List<Line>>, which lies in line_list.dart files : 

	














    

		

        

            
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I have a custom class that fetches data from the database, that returns Future<List<Line>>, which lies in line_list.dart files : 














android - 如何返回未来 and assign it to just object , flutter

I have a custom class that fetches data from the database, that returns Future<List<Line>>, which lies in line_list.dart files : 







问题描述



I have a custom class that fetches data from the database, that returns Future<List<Line>>, which lies in line_list.dart files : 



  Future<List<Line>> fetchingLinesData() async {
    List<Line> lineList = [];
    var databasesPath = await getDatabasesPath();
    String path = join(databasesPath, 'main.db');
    Database database = await openDatabase(path, version: 1);
    database.transaction((tnx) async {
      dbRef.child('line').once().then((DataSnapshot dataSnapshot) async {
        dataSnapshot.value.forEach((key, value) async {
          List<Station> inLineStations = [];
          for (var i = 0; i < 100; i++) {
            if (value["station_$i"] != null) {
              List<Map> stations = await tnx.rawQuery("SELECT * FROM Station");
              stations.forEach((s) {
                if (s['stationName'] == value["station_$i"]) {
                  Station stationInstance = Station(
                      key: s['key'],
                      cityName: s['cityName'],
                      stationName: s['stationName'],
                      stationLongitude: s['stationLongitude'],
                      stationLatitude: s['stationLatitude']);
                  inLineStations.add(stationInstance);
                }
              });
            }
          }
          Line lineInstance = Line(
              startStation: value['start_station'],
              endStation: value['end_station'],
              inLineStations: inLineStations,
              notes: value['notes'],
              price: value['price'],
              transportationType: value['transportation_type']);
          lineList.add(lineInstance);
        });
      });
    });
    return lineList;
  }
}




and then in my main.dart widget, I have this : 



List<Line> allLines = [];




I want to do something like this : 



allLines = LinesList().fetchingLinesData();




But of course, it gives me an error as am trying to assign Future<List<Line>> to List<Line>



how to do it?







Better way compare nodes in a list


Noob, trying to add 'unique' Nodes to a list, i.e. with my simple code, I only want the 2 unique nodes, not any duplicate entries. I found a poor workaround, where I created a temp list, added the values (as list items, not as nodes) to the temp list if unique, and then added all items from temp to my list of Nodes (converting them to Nodes at that point), but I'm sure there's a better much cleaner way to do this.  



class Node():
    # current actor, source, movie
    def __init__(self, state, parent, action):
        self.state = state
        self.parent = parent
        self.action = action

x = Node(5,4,3)
y = Node(5,4,2)
z = Node(5,4,3)

listz = []

if x not in listz:
    listz.append(x)

if y not in listz:
    listz.append(y)

if z not in listz:
    listz.append(z)

for item in listz:
    print(item.state, item.parent, item.action)

Current Outputs (incorrect):
5 4 3
5 4 2 
5 4 3

Should Output (correct):
5 4 3
5 4 2 




Simple solutions I can follow and implement are preferred to clever ones I can't.


标签： androidiosflutterasynchronousdart


解决方案









您必须等待未来完成。



allLines = await LinesList().fetchingLinesData();











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