Widget build(BuildContext context) {

    List<Widget> _filterFields() {
      return [
        Text('Filtros', style: TextStyle(fontSize: 24.0),),
        SwitchListTile(
          title: Text('Mostrar perdidos'),
          value: _mapFilterObjectives[Objective.lost],
          onChanged: (v) {
            print(v);
            print(_mapFilterObjectives[Objective.lost]);
            setState(() {
              _mapFilterObjectives[Objective.lost] = !_mapFilterObjectives[Objective.lost];
            });
          },
        ),
        // ...
      ];
    }

    void _markersFilterSheet(BuildContext context) {
      showModalBottomSheet<void>(
        context: context,
        builder: (BuildContext context) {
          return Material(
            color: Colors.white,
            child: Padding(
              padding: EdgeInsets.all(10.0),
              child: Column(
                mainAxisSize: MainAxisSize.min,
                children: _filterFields()
              )
            )
          );
        }
      );
    }

    return Scaffold(
      key: _scaffoldKey,
      drawer: builDrawer(context, route),
      body: Builder(
        builder: (context) {
          return Stack(
            children: <Widget>[
              // ...
              Positioned(
                right: 20.0,
                top: 40.0,
                child: SizedBox(
                  width: 40.0,
                  height: 40.0,
                  child: FloatingActionButton(
                    child: Icon(Icons.filter_list, color: Colors.blue, size: 25.0,),
                    onPressed: () {
                      _markersFilterSheet(context);
                    },
                    backgroundColor: Colors.white,
                  )
                ),
              ),
            ],
          );
        },
      ),
    );
  }
}