点击标记后无法使用Map_view在地图中绘制路线

Question

我正在将map_view用于停车场应用程序。我想做的是当用户点击标记时绘制到标记的路线。

    //This is where i get latlong from current location to destination
network
    .get("origin=" +
        "6.8740348" +
        "," +
        "79.8815354" +
        "&destination=" +
        destinationLat.toString() +
        "," +
        destinationLng.toString() +
        "&key=AIzaSyBBC77865U0RsHg7kE2LmuROaMQTPiSW28")
    .then((dynamic res) {
  List<Steps> rr = res;
  print("Print Res");
  print(location.latitude.toString());
  print(location.longitude.toString());
  print(destinationLat.toString());
  print(destinationLng.toString());
  print("Print List");
  print(rr);

  directionsArray = new List();
  for (final i in rr) {
    directionsArray.add(i.startLocation);
    directionsArray.add(i.endLocation);
    print("Print i");
    print(i);
    print("Print ccc");
    print(directionsArray);
    drawLine(ccc);
  }
    //Drawing the polyline 
  mapView.addPolyline(
      new Polyline("11", directionsArray, width: 15.0, color: Colors.blue));
  setState(() {
  count++;
  print(count);
});
  setState(() {});
});

在绘制一条路线后，点击另一条标记时出现错误。它不会画。我尝试使用setState，但无法正常工作。