Question

<script>
// holds an instance of XMLHttpRequest
var xmlHttp = createXmlHttpRequestObject();

// creates an XMLHttpRequest instance
function createXmlHttpRequestObject()
{
  // will store the reference to the XMLHttpRequest object
  var xmlHttp;
  // this should work for all browsers except IE6 and older
  try
  {
    // try to create XMLHttpRequest object
    xmlHttp = new XMLHttpRequest();
  }
  catch(e)
  {
    // assume IE6 or older
    var XmlHttpVersions = new Array("MSXML2.XMLHTTP.6.0",
                                    "MSXML2.XMLHTTP.5.0",
                                    "MSXML2.XMLHTTP.4.0",
                                    "MSXML2.XMLHTTP.3.0",
                                    "MSXML2.XMLHTTP",
                                    "Microsoft.XMLHTTP");
    // try every prog id until one works

    for (var i=0; i<XmlHttpVersions.length && !xmlHttp; i++)
    {
      try
      {
        // try to create XMLHttpRequest object
        xmlHttp = new ActiveXObject(XmlHttpVersions[i]);
      }
      catch (e) {}
    }
  }
  // return the created object or display an error message
  if (!xmlHttp)
    <?fwrite($log,"Error creating the XMLHttpRequest object.")?>;
  else
    return xmlHttp;
}

// read a file from the server
function process()
{
  // only continue if xmlHttp isn't void
  if (xmlHttp)
  {
    // try to connect to the server
    try
    {
      // initiate reading a file from the server
      xmlHttp.open("GET", "update.php?id=".$_GET['id']."", true);
      xmlHttp.onreadystatechange = handleRequestStateChange;
      xmlHttp.send(null);
    }
    // display the error in case of failure
    catch (e)
    {
    <?  fwrite($log,"Can't connect to server:\n")?>;
    }
  }
}


// function called when the state of the HTTP request changes
function handleRequestStateChange()
{
  // when readyState is 4, we are ready to read the server response
  if (xmlHttp.readyState == 4)
  {
    // continue only if HTTP status is "OK"
    if (xmlHttp.status == 200)
    {
      try
      {
        // do something with the response from the server
        handleServerResponses();
      }
      catch(e)
      {
        // display error message
        <? fwrite($log,"Error reading the response: ");?>
      }
    }
    else
    {
      // display status message
     <? fwrite($log,"There was a problem retrieving the data:\n");?>

    }
  }
}

// handles the response received from the server
function handleServerResponses()
{
  // read the message from the server
  var xmlResponse = xmlHttp.responseXML;
  // catching potential errors with IE and Opera
  if (!xmlResponse || !xmlResponse.documentElement)
  throw("Invalid XML structure:\n" + xmlHttp.responseText);
  // catching potential errors with Firefox
var rootNodeName = xmlResponse.documentElement.nodeName;
if (rootNodeName == "parsererror") throw("Invalid XML structure");
  // obtain the XML's document element
  xmlRoot = xmlResponse.documentElement; 
  // obtain arrays with book titles and ISBNs
  titleArray = xmlRoot.getElementsByTagName("title");
  isbnArray = xmlRoot.getElementsByTagName("isbn");
  // generate HTML output
  // iterate through the arrays and create an HTML structure
  latc = titleArray.item(0).firstChild.data;
  lonc = isbnArray.item(0).firstChild.data;
  lonc = parseFloat(lonc);
latc = parseFloat(latc);
  setInterval('process()',17000);
         var lonLat1 = new OpenLayers.LonLat(lonc,latc)
             .transform(new OpenLayers.Projection("EPSG:4326"), // преобразование из WGS 1984
                                    new OpenLayers.Projection("EPSG:900913")
                                            );
                map.setCenter(lonLat1, 16);
                var icon = new OpenLayers.Icon('images/car.png', size, offset);
                var size = new OpenLayers.Size(21,25);
                var offset = new OpenLayers.Pixel(-(size.w/2), -size.h);
                marker2 = new OpenLayers.Layer.Markers( "Car" );
                map.addLayer(marker2);
                marker2.addMarker(new OpenLayers.Marker(lonLat1,icon));
}   
function init()
          {

        map = new OpenLayers.Map("basicMap");
        var mapnik = new OpenLayers.Layer.OSM();
        map.addLayer(mapnik);
        lat = <? //echo $lat ?>;
        lon = <? //echo $lon ?>;

            var lonLat = new OpenLayers.LonLat(lon,lat)
                      .transform(new OpenLayers.Projection("EPSG:4326"), // преобразование из WGS 1984
                                    new OpenLayers.Projection("EPSG:900913")
                                            );

            marker = new OpenLayers.Layer.Markers( "Marker" );
            map.addLayer(marker);
            var size = new OpenLayers.Size(21,25);
            var offset = new OpenLayers.Pixel(-(size.w/2), -size.h);
            var icon = new OpenLayers.Icon('images/marker-def.png', size, offset);
            marker.addMarker(new OpenLayers.Marker(lonLat,icon.clone()));
    }
        </script>
  </head>
   <body onload="process(); init()">

如何在更新新标记后删除以前的标记2？

Answer 1

在使用新标记添加新图层之前，您应该使用旧标记删除图层。所以，在

之前

marker2 = new OpenLayers.Layer.Markers( "Car" );    
map.addLayer(marker2);

你应该致电

map.removeLayer(map.getLayersByName('Marker')[0]);

但这太过分了。您应该只使用一个标记图层，并使用方法addMarker和removeMarker

添加/删除标记

如何删除以前的标记？

1 个答案: