Flutter - 一段时间后自动刷新地图上标记的图标

Question

我有一些标记，标记的图标根据 firebase 字段（称为状态）而变化。 status 是一个布尔值 (true/false)。外部应用程序经常在数据库中更改此状态值，因此我需要能够根据字段的当前值更新图标。如何自动更新 UI 上的标记？

这是我的代码：

BitmapDescriptor customFreeLotIcon, customOccupiedLotIcon;
Future<List<Marker>> _createMarkersForLotsAndParkings() async{
   List<Marker> markersList = [];
   int markerId = 0;
    QuerySnapshot subDocuments = await parkingDocReference.collection("lots").get();
    List<DocumentSnapshot> subDocumentsSnapshots = subDocuments.documents;
    for (DocumentSnapshot subDoc in subDocumentsSnapshots){
         String subDocId = subDoc.documentID;
         DocumentSnapshot snapshot = await parkingDocReference.collection("lots")
         .document(subDocId).get();
            print(snapshot.get('location').latitude);
            markersList.add(
              Marker(
                  markerId:MarkerId(markerId.toString()),
                  position: LatLng(snapshot.get('location').latitude,
                      snapshot.get('location').longitude),
                  onTap: () => _changeMap(LatLng(
                      snapshot.get('location').latitude,
                      snapshot.get('location').longitude)),
                  icon: snapshot.get('status') == true ? customOccupiedLotIcon : customFreeLotIcon ),
            );
            markerId++;      
     }
}
return Future.value(markersList);

}


 createCustomImageForParkingsMarkers(context){
    if (customFreeLotIcon == null) {
      ImageConfiguration configuration = createLocalImageConfiguration(context);
      BitmapDescriptor.fromAssetImage(configuration, 'assets/freeLots.png')
          .then((icon) {
        setState(() {
          customFreeLotIcon = icon;
        });
      });
    }
    else if (customOccupiedLotIcon == null) {
      ImageConfiguration configuration = createLocalImageConfiguration(context);
      BitmapDescriptor.fromAssetImage(configuration, 'assets/occupiedLots.png')
          .then((icon) {
        setState(() {
          customOccupiedLotIcon = icon;
        });
      });
    }
  }

Answer 1

尝试添加监听器：

BitmapDescriptor customFreeLotIcon, customOccupiedLotIcon;
Future<List<Marker>> _createMarkersForLotsAndParkings() async{
   List<Marker> markersList = [];
   int markerId = 0;
    QuerySnapshot subDocuments = await parkingDocReference.collection("lots").get();
    List<DocumentSnapshot> subDocumentsSnapshots = subDocuments.documents;
    for (DocumentSnapshot subDoc in subDocumentsSnapshots){
         String subDocId = subDoc.documentID;
         DocumentSnapshot snapshot = await parkingDocReference.collection("lots")
         .document(subDocId).snapshots()
        .listen((DocumentSnapshot documentSnapshot) async {
      Map<String, dynamic> document = documentSnapshot.data();
            print(document['location'].latitude);
            markersList.add(
              Marker(
                  markerId:MarkerId(markerId.toString()),
                  position: LatLng(document['location'].latitude,
                      document['location'].longitude),
                  onTap: () => _changeMap(LatLng(
                     document['location'].latitude,
                      document['location'].longitude)),
                  icon: document['status'] == true ? customOccupiedLotIcon : customFreeLotIcon ),
            );
            markerId++;   
}   
     }
}
return Future.value(markersList);

}


 createCustomImageForParkingsMarkers(context){
    if (customFreeLotIcon == null) {
      ImageConfiguration configuration = createLocalImageConfiguration(context);
      BitmapDescriptor.fromAssetImage(configuration, 'assets/freeLots.png')
          .then((icon) {
        setState(() {
          customFreeLotIcon = icon;
        });
      });
    }
    else if (customOccupiedLotIcon == null) {
      ImageConfiguration configuration = createLocalImageConfiguration(context);
      BitmapDescriptor.fromAssetImage(configuration, 'assets/occupiedLots.png')
          .then((icon) {
        setState(() {
          customOccupiedLotIcon = icon;
        });
      });
    }
  }

在此处添加Setstate()：

setState(() {
      markersList.add(
        Marker(
            markerId:MarkerId(markerId.toString()),
            position: LatLng(document['location'].latitude,
                document['location'].longitude),
            onTap: () => _changeMap(LatLng(
                document['location'].latitude,
                document['location'].longitude)),
            icon: document['status'] == true ? customOccupiedLotIcon : customFreeLotIcon ),
      );
      markerId++;
    });