Google Maps V3：定期更新标记

Question

我一直在 这里
找到有关Google Maps上的PHP / MYSQL教程。

我希望每5秒钟左右从数据库更新一次标记。

据我了解，我需要使用Ajax定期更新标记，但是我很难理解要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没有真正说明正在发生的事情，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() {}

我希望有人能帮助我！

Answer 1

请注意，我没有对此进行测试，因为我没有方便的xml数据库

首先，您需要将load（）函数拆分为用于初始化地图并在domready上加载标记的函数，以及稍后将用于处理xml和更新地图的函数。需要这样做，因此您不必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地图上已经绘制的标记。为此，您需要在将它们添加到地图时将它们添加到数组。在第二次更新中，您可以选择重绘标记（重建阵列）或仅更新现有阵列。我的示例显示了一个场景，您只需从屏幕上清除旧标记即可（这比较简单）。

//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);
    }