Google Maps V3：定期更新标记

Question

我在谷歌地图上找到了 PHP/MYSQL 教程 here。

我希望每 5 秒左右从数据库中更新一次标记。

据我了解，我需要使用 Ajax 定期更新标记，但我很难理解在哪里添加函数以及在哪里使用 setTimeout() 等

我发现的所有其他示例并不能真正解释发生了什么，一些有用的指导会很棒！

这是我的代码（与 Google 示例相同，但有一些 var 更改）：

function load() {
  var map = new google.maps.Map(document.getElementById("map"), {
    center: new google.maps.LatLng(37.80815648152641, 140.95355987548828),
    zoom: 13,
    mapTypeId: 'roadmap'
  });
  var infoWindow = new google.maps.InfoWindow;

  // Change this depending on the name of your PHP file

  downloadUrl("nwmxml.php", function(data) {
    var xml = data.responseXML; 
    var markers = xml.documentElement.getElementsByTagName("marker");
    for (var i = 0; i < markers.length; i++) {
      var host = markers[i].getAttribute("host");
      var type = markers[i].getAttribute("active");
      var lastupdate = markers[i].getAttribute("lastupdate");
      var point = new google.maps.LatLng(
          parseFloat(markers[i].getAttribute("lat")),
          parseFloat(markers[i].getAttribute("lng")));
      var html = "<b>" + "Host: </b>" + host + "<br>" + "<b>Last Updated: </b>" + lastupdate + "<br>";
      var icon = customIcons[type] || {};
      var marker = new google.maps.Marker({
        map: map,
        position: point,
        icon: icon.icon,
        shadow: icon.shadow
      });
      bindInfoWindow(marker, map, infoWindow, html);

    }

  });
}

function bindInfoWindow(marker, map, infoWindow, html) {
  google.maps.event.addListener(marker, 'click', function() {
    infoWindow.setContent(html);
    infoWindow.open(map, marker);
  });
}

function downloadUrl(url, callback) {
  var request = window.ActiveXObject ?
      new ActiveXObject('Microsoft.XMLHTTP') :
      new XMLHttpRequest;

  request.onreadystatechange = function() {
    if (request.readyState == 4) {
      request.onreadystatechange = doNothing;
      callback(request, request.status);
    }
  };

  request.open('GET', url, true);
  request.send(null);
}

function doNothing() {}

希望有人能帮帮我！

Answer 1

请注意，我没有对此进行测试，因为我没有带 xml 的数据库

首先，您需要将 load() 函数拆分为一个初始化地图并在 domready 上加载标记的函数，以及一个稍后将用于处理 xml 并更新地图的函数。需要这样做，这样您就不会在每次加载时都重新初始化地图。

其次，您需要决定如何处理已在地图上绘制的标记。为此，您需要在将它们添加到地图时将它们添加到数组中。在第二次更新时，您可以选择重绘标记（重建数组）或简单地更新现有数组。我的示例显示了您只需从屏幕上清除旧标记的场景（这更简单）。

//global array to store our markers
    var markersArray = [];
    var map;
    function load() {
        map = new google.maps.Map(document.getElementById("map"), {
            center : new google.maps.LatLng(37.80815648152641, 140.95355987548828),
            zoom : 13,
            mapTypeId : 'roadmap'
        });
        var infoWindow = new google.maps.InfoWindow;

        // your first call to get & process inital data

        downloadUrl("nwmxml.php", processXML);
    }

    function processXML(data) {
        var xml = data.responseXML;
        var markers = xml.documentElement.getElementsByTagName("marker");
        //clear markers before you start drawing new ones
        resetMarkers(markersArray)
        for(var i = 0; i < markers.length; i++) {
            var host = markers[i].getAttribute("host");
            var type = markers[i].getAttribute("active");
            var lastupdate = markers[i].getAttribute("lastupdate");
            var point = new google.maps.LatLng(parseFloat(markers[i].getAttribute("lat")), parseFloat(markers[i].getAttribute("lng")));
            var html = "<b>" + "Host: </b>" + host + "<br>" + "<b>Last Updated: </b>" + lastupdate + "<br>";
            var icon = customIcons[type] || {};
            var marker = new google.maps.Marker({
                map : map,
                position : point,
                icon : icon.icon,
                shadow : icon.shadow
            });
            //store marker object in a new array
            markersArray.push(marker);
            bindInfoWindow(marker, map, infoWindow, html);


        }
            // set timeout after you finished processing & displaying the first lot of markers. Rember that requests on the server can take some time to complete. SO you want to make another one
            // only when the first one is completed.
            setTimeout(function() {
                downloadUrl("nwmxml.php", processXML);
            }, 5000);
    }

//clear existing markers from the map
function resetMarkers(arr){
    for (var i=0;i<arr.length; i++){
        arr[i].setMap(null);
    }
    //reset the main marker array for the next call
    arr=[];
}
    function bindInfoWindow(marker, map, infoWindow, html) {
        google.maps.event.addListener(marker, 'click', function() {
            infoWindow.setContent(html);
            infoWindow.open(map, marker);
        });
    }

    function downloadUrl(url, callback) {
        var request = window.ActiveXObject ? new ActiveXObject('Microsoft.XMLHTTP') : new XMLHttpRequest;

        request.onreadystatechange = function() {
            if(request.readyState == 4) {
                request.onreadystatechange = doNothing;
                callback(request, request.status);
            }
        };

        request.open('GET', url, true);
        request.send(null);
    }

Answer 2

setInterval(function() { 
    downloadUrl("conection/cargar_tecnicos.php", function(data) {

        var xml = data.responseXML;
         markers = xml.documentElement.getElementsByTagName("marker");
         removeAllMarkers();
        for (var i = 0; i < markers.length; i++) {
              var name = markers[i].getAttribute("name");
            var fecha = markers[i].getAttribute("fecha");
            var id_android = markers[i].getAttribute("id_android");
            var celular = markers[i].getAttribute("celular");
            var id = markers[i].getAttribute("id");
            var logo = markers[i].getAttribute("logo");
            var type = markers[i].getAttribute("type");
            var point = new google.maps.LatLng(
                    parseFloat(markers[i].getAttribute("lat")),
                    parseFloat(markers[i].getAttribute("lng")));

           var html = "<div class='infowindow'>"
                        +"<br/><div style='text-align:center;'><img src="+logo+"><br/>"    
                        +"<b>" + name + "</b></div><br/>"
                        +"<br/><label><b>Celular:</b></label>" + celular+""
                        +"<br/><label><b>Id Android:</b></label>" + id_android+""
                        +"<br/><label><b>Fecha y Hora:</b></label>" + fecha+""
                        +"<br/><br/><div style='text-align:center;'><a><input style=';' id='pop' type='image' value='"+id+"' class='ASD' img src='img/vermas.png' title='Detalles'/></a></div></div>";
            var icon = customIcons[type] || {};
             marker[i] = new google.maps.Marker({ 
                position: point,
                icon: icon.icon,
                shadow: icon.shadow,
                title:name
            });

            openInfoWindow(marker[i], map, infoWindow, html);   
          marker[i].setMap(map);
        }
    });

},10000);
}
function removeAllMarkers(){// removes all markers from map
    for( var i = 0; i < marker.length; i++ ){
            marker[i].setMap(null);
}
}