Question

我正在使用一个下拉按钮来更新用户周围餐馆的位置，但是这些位置在ListView中没有更新。这是我到目前为止的内容：

编辑：添加了Init语句

初始化声明

@override
  void initState() {
    _dropDownMenuItems = buildAndGetDropDownMenuItems(changeDistance);
    _mapDropdownFilter = _dropDownMenuItems[0].value;
    filterMarker(userLat, userLong, dispensaries, 1);

    super.initState();


  }

我开设了一个班级来协助这个所谓的地点

class Locations{
  final Restaurant dis;
  final double dist;
  final int index;
  Locations({this.dis, this.dist, this.index});
}

然后调用此过滤器以按距离对我的位置进行排序，并给他们与用户之间的距离（以英里为单位）：

  Future filterMarker(userLat, userLong, restaurants, filterdis) async {
    Set<Marker> _tmpMarkers = Set();
    final Uint8List markerIcon =
        await getBytesFromAsset('assets/smiley.png', 100);

    int filterCounter = 0;
    List<Locations> _tmpLocation = List();
    for (int i = 0; i < restaurant.length; ++i) {
      Geolocator()
          .distanceBetween(
              userLat, userLong, restaurants[i].lat, restaurants[i].long)
          .then((calcDist) {
        print(calcDist);
        if (calcDist / 1000 < filterdis) {
          filterCounter++;
          final String markerIdVal = 'marker_id_$filterCounter';

          final MarkerId markerId = MarkerId(markerIdVal);
          var dis = calcDist / 1000;
          var distances = dis.toStringAsFixed(2);
          // creating a new MARKER
          _tmpMarkers.add(Marker(
              markerId: markerId,
              position: LatLng(restaurants[i].lat, restaurants[i].long),
              infoWindow: InfoWindow(
                  title: restaurants[i].name, snippet: '$distances mi Away'),
              icon: BitmapDescriptor.fromBytes(markerIcon)));
          _tmpLocation.add(
              Locations(index: i, dis: restaurants[i], dist: calcDist / 1000));
        }
      });
      setState(() {
        _filteredMarkers = _tmpMarkers;
        filteredVenues = _tmpLocation.cast<Locations>();
      });

      print('Do once');
    }
    print('There are ${filteredVenues.length} _filteredMarkers');
  }

我的下拉按钮的设置如下：

DropdownButton(
                      style: TextStyle(
                          fontFamily: 'Roboto-Regular',
                          color: Colors.black),
                      elevation: 6,
                      icon: Icon(
                        FontAwesomeIcons.angleRight,
                        color: buddiesGreen,
                      ),
                      value: _mapDropdownFilter,
                      items: _dropDownMenuItems,
                      onChanged: _changeFilterList,
                    )

填写以下内容：

//Distance Map filter Button
  final List changeDistance = ['1', '5 ', '10 ', '20'];
  // Set<Marker> _filteredMarkers = Set();
  List<Locations> filteredVenues;
  var _filteredMarkers;
  var filteredRestaurant;

    _dropDownMenuItems = buildAndGetDropDownMenuItems(changeDistance);
    _mapDropdownFilter = _dropDownMenuItems[0].value;

  String _mapDropdownFilter;
  List<DropdownMenuItem<String>> _dropDownMenuItems;

  List<DropdownMenuItem<String>> buildAndGetDropDownMenuItems(List tempList) {
    List<DropdownMenuItem<String>> items = List();
    for (String x in tempList) {
      items.add(DropdownMenuItem(
          value: x,
          child: Text(
            x,
            style: TextStyle(
                fontSize: 14,
                fontFamily: 'Roboto-Regular',
                fontWeight: FontWeight.w700,
                color: buddiesPurple),
          )));
    }

    return items;
  }

void _changeFilterList(String value) {
    //use _filterDropdown for switch statement
    setState(() {
      _mapDropdownFilter = value;
    });
    _sortProductsDropDown(_mapDropdownFilter);

    print(_mapDropdownFilter);
  }

  void _sortProductsDropDown(_mapDropdownFilter) {
    switch (_mapDropdownFilter) {
      case '1 Mile':
        print('1 Mile');
        filterMarker(userLat, userLong, restaurant, 1);
        print(restaurant.length);
        break;
      case '5 Miles':
        filterMarker(userLat, userLong, restaurant, 5);
        print(restaurant.length);

        break;
      case '10 Miles':
        filterMarker(userLat, userLong, restaurant, 10);
        print(restaurant.length);

        break;
      case '20 Miles':
        filterMarker(userLat, userLong, restaurant, 20);
        print(restaurant.length);

        break;
    }
  }

当我点击下拉列表（断开连接是什么）时，它没有更新，为什么当用户选择不同的距离时它没有更新。

Answer 1

因为您没有在initState（）中使用setState（）来获取位置列表。因此，即使您正确获取所有内容，位置状态也不会更新。

.. setState(){ _dropDownMenuItems = buildAndGetDropDownMenuItems(changeDistance); .. } 做这样的事情。

无法使用下拉按钮和未来的颤振更新数组

1 个答案: