每 X 秒用 mysql 数据更新 google java map

Question

我正在尝试每 X 秒更新一次地图上的标记。地图可以很好地加载初始数据，但如何只刷新标记（而不是整个地图）..
我的代码非常简单。我对 php 和 mysql 有很好的了解，但我缺乏足够的 java 知识来完成这个任务。

<script>
  var customLabel = {
    restaurant: {
      label: 'R'
    },
    bar: {
      label: 'B'
    }
  };

    function initMap() {
    var map = new google.maps.Map(document.getElementById('map'), {
      center: new google.maps.LatLng(51.337834, 5.222728),
      zoom: 7
    });
    var infoWindow = new google.maps.InfoWindow;

      downloadUrl('http://myurl.php', function(data) {
        var xml = data.responseXML;
        var markers = xml.documentElement.getElementsByTagName('marker');
        Array.prototype.forEach.call(markers, function(markerElem) {
          var name = markerElem.getAttribute('name');
          var address = markerElem.getAttribute('address');
          var type = markerElem.getAttribute('type');
          var point = new google.maps.LatLng(
              parseFloat(markerElem.getAttribute('lat')),
              parseFloat(markerElem.getAttribute('lng')));

          var infowincontent = document.createElement('div');
          var strong = document.createElement('strong');
          strong.textContent = name
          infowincontent.appendChild(strong);
          infowincontent.appendChild(document.createElement('br'));

          var text = document.createElement('text');
          text.textContent = address
          infowincontent.appendChild(text);
          var icon = customLabel[type] || {};
          var marker = new google.maps.Marker({
            map: map,
            position: point,
            label: icon.label
          });
          marker.addListener('click', function() {
            infoWindow.setContent(infowincontent);
            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() {}
</script>
<script async defer
src="https://maps.googleapis.com/maps/api/js?key=APIKEY&callback=initMap">
</script>

我有一种强烈的感觉，我需要在某个地方使用 setInterval 函数。但是我尝试了几次，例如把它作为这个小部分；

setInterval(function() { 
downloadUrl('http://myurl.p....
}, 5000);

但运气不好……有什么想法吗？

更新

我设法使用下面的代码让它工作..我不知道这是否是最有效的方法..现在我得到了显示轨迹的额外标记..所以我仍然需要一种方法来首先清除所有放置新标记之前的标记；

    downloadUrl('myurl.php', function(data) {
        var xml = data.responseXML;
        var markers = xml.documentElement.getElementsByTagName('marker');
        Array.prototype.forEach.call(markers, function(markerElem) {
          var name = markerElem.getAttribute('name');
          var address = markerElem.getAttribute('address');
          var type = markerElem.getAttribute('type');
          var point = new google.maps.LatLng(
              parseFloat(markerElem.getAttribute('lat')),
              parseFloat(markerElem.getAttribute('lng')));

          var infowincontent = document.createElement('div');
          var strong = document.createElement('strong');
          strong.textContent = name
          infowincontent.appendChild(strong);
          infowincontent.appendChild(document.createElement('br'));

          var text = document.createElement('text');
          text.textContent = address
          infowincontent.appendChild(text);
          var icon = customLabel[type] || {};
          var marker = new google.maps.Marker({
            map: map,
            position: point,
            label: icon.label
          });
          marker.addListener('click', function() {
            infoWindow.setContent(infowincontent);
            infoWindow.open(map, marker);
          });
        });
},5000); 
      });
    }

Answer 1

您使用了很多只使用一次的变量。你冷压缩你的代码。此外，我为您的标记添加了一个数组，以便您可以通过函数清理它们。这个函数也可以在你调用 downloadUrl 之前调用，而不是在那里添加它：

var myMarkers = [];

downloadUrl('myurl.php', function(data) {
    var xml = data.responseXML;
    clearMarkers();
    var markers = xml.documentElement.getElementsByTagName('marker');
    Array.prototype.forEach.call(markers, function(markerElem) {
        var infowincontent = document.createElement('div');
        var strong = document.createElement('strong');
        strong.textContent = markerElem.getAttribute('name')
        infowincontent.appendChild(strong);
        infowincontent.appendChild(document.createElement('br'));

        var text = document.createElement('text');
        text.textContent = markerElem.getAttribute('address')
        infowincontent.appendChild(text);
        var icon = customLabel[markerElem.getAttribute('type')] || {};
        var marker = new google.maps.Marker({
            map: map,
            position: new google.maps.LatLng(
                parseFloat(markerElem.getAttribute('lat')),
                parseFloat(markerElem.getAttribute('lng')));,
            label: icon.label
        });
        marker.addListener('click', function() {
            infoWindow.setContent(infowincontent);
            infoWindow.open(map, marker);
        });
        myMarkers.push(marker);
    });
}, 5000);

function clearMarkers() {
    for (var i = 0; i < myMarkers.length; i++) {
        myMarkers[i].setMap(null);
    }
    myMarkers.length = 0;
}

应该可以。