Flutter listview with slider to pick radius for nearby users

I'm trying to make slider to pick radius:

FlutterSlider(
          values: [150],
          min: 0,
          max: 150,

          onDragging: (handlerIndex, lowerValue, upperValue) {
            radius = lowerValue;
            fut = _gdb.getUsersInRadius(radius);
          },
        ),

And I have listview which is getting users nearby to our location:

Expanded(
          child: FutureBuilder(
            future: fut,
            builder: (BuildContext context, AsyncSnapshot<dynamic> snapshot) {
              if(!snapshot.hasData){
                return Center(
                    child: Text("No users"));
                   }
              return StreamBuilder(
                stream: snapshot.data,
                builder: (BuildContext context, AsyncSnapshot<dynamic> snapshot) {
                  if(!snapshot.hasData){
                    return Center(
                        child: Text("No users"));
                       }else{
                         print(snapshot.data.length);
                         users.addAll(snapshot.data);
                         return ListView.builder(
                             controller: _scrollController ,
                             itemCount: users.length,
                             itemBuilder: (BuildContext ctx, int index){

                                 return ListTile(
                                   title: Text(users[index].data['username']),
                                  );
                             });
                       }
                     },
                   );
                 },
               ),
             )

Now I want to get users only close to us with selected radius in slider