Question

I have this function that after a click on a marker draws a line between points that are related to an item.

function showDetails(itemId)
{   
    var newlatlng = itemId.position;
    var xmlhttp;

    if (window.XMLHttpRequest)
    {// code for IE7+, Firefox, Chrome, Opera, Safari
        xmlhttp=new XMLHttpRequest();
    }
    else
    {// code for IE6, IE5
        xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
    }

    xmlhttp.open("GET", "index.php?r=items/ajaxdetails&id="+itemId.indice, 
                 false);
    xmlhttp.send();




    var checkins = JSON.parse(xmlhttp.responseText);
    var numeroCheckins = checkins.length;

    var polylineCheckins = [];

    var bounds = new google.maps.LatLngBounds();

    for (counter = 0; counter< numeroCheckins; counter++)
    {
        var posizione = new google.maps.LatLng(checkins[counter].lat,
                                               checkins[counter].long);
        polylineCheckins[counter] = posizione;
        bounds.extend(posizione);
    }

    var polyline = new google.maps.Polyline({
        path: polylineCheckins,
        strokeColor: "#FF0000",
        strokeOpacity: 0.5,
        strokeWeight: 5
        });

    polyline.setMap(map);

    map.fitBounds(bounds);
}

Everything is working, but if a call several time this function the previous line is always showed. I tried to use the method setMap(null) but without success, to try to reset the polyline.

I would like to achieve te result of deleting the previous polyline, before drawing a new one.

Thanks for your support

Answer 1

The easiest way to keep only one Polyline for showDetails on the map is to make a global Polyline variable. That way, each time showDetails is called the global variable is modified.

Right now, each time showDetails runs a new Polyline is created and no reference to it is returned, so I don’t see a way to set the previous line’s map to null.

  // GLOBAL 
  var detailsPolyline = new google.maps.Polyline({
    strokeColor: "#FF0000",
    strokeOpacity: 0.5,
    strokeWeight: 5
  });

inside showDetails:

detailsPolyline.setPath(polylineCheckins);
detailsPolyline.setMap(map);

map.fitBounds(bounds);

Here’s the whole test case I used, because I don’t have the php file I created my own objects

  var map;
  var mapOptions = { center: new google.maps.LatLng(0.0, 0.0), zoom: 2,
    mapTypeId: google.maps.MapTypeId.ROADMAP };

  function initialize() {
    map = new google.maps.Map(document.getElementById("map_canvas"), mapOptions);
    showDetails([ {lat: 20, long: 0},
                  {lat: 20, long: 10},
                  {lat: 30, long: 20}]);

    showDetails([ {lat: 10, long: 0},
                  {lat: 10, long: 10},
                  {lat: 20, long: 20}]);
  }

  var detailsPolyline = new google.maps.Polyline({
    strokeColor: "#FF0000",
    strokeOpacity: 0.5,
    strokeWeight: 5
  });

function showDetails(checkins)
{   
    var numeroCheckins = checkins.length;
    var polylineCheckins = [];
    var bounds = new google.maps.LatLngBounds();

    for (counter = 0; counter< numeroCheckins; counter++)
        {
        var posizione = new google.maps.LatLng(checkins[counter].lat, checkins[counter].long);
        polylineCheckins[counter] = posizione;
        bounds.extend(posizione);
        }

    detailsPolyline.setPath(polylineCheckins);
    detailsPolyline.setMap(map);

    map.fitBounds(bounds);
}