javascript - 如何修复 "DownloadURL gives responseXML null value"

Question

我正在开发一个Web UI并使用动态downloadURl方法来获取输出和php(testing.php)文件并进一步处理它，php文件提供了有效的xml文件输出，但在downloadURl函数中它给出了responseXML=null错误。有时 UI 能够获取响应 XML，但大多数时候它返回 null 值。

这是我的 downloadURL 文件代码

  downloadUrl("testing.php", function(data) {
        console.log(data);
        var xml = data.responseXML;
        var markers = xml.documentElement.getElementsByTagName("marker");
        for (var i = 0; i < markers.length; i++) {
          var name = markers[i].getAttribute("Chainage");
          var address = markers[i].getAttribute("address");
                   var temperkey = markers[i].getAttribute("temperkey");
                  var vibration = markers[i].getAttribute("vibration");
                  var batterystatus = markers[i].getAttribute("batterystatus");
                  var lt = markers[i].getAttribute("lat");
                  var lg = markers[i].getAttribute("lng");

          var status = markers[i].getAttribute("status");

          var point = new google.maps.LatLng(
              parseFloat(markers[i].getAttribute("lat")),
              parseFloat(markers[i].getAttribute("lng")));
          var html = "<b>"+'Chainage:'+"</b>"+"<b>"+ name + "</b> <br/>"+"<b>"+'LAT:'+"</b>"+"<b>"+ lt + "</b> <br/>"+"<b>"+'LONG:'+"</b>"+"<b>"+ lg + "</b> <br/>"+"<b>"+'EcbNo:'+"</b>"+'<a id="ancid" href="#" onclick="return check()">'+address+'</a>';
    var icon = customIcons[status] || {};
                  var img1='12.png';
                 if(status==1)
                        {
                           img1='13.png';
                                //var  img2='Phonehandset.gif';
                        }
                  if(temperkey==1||vibration==1)
                        {
                           img1='14.png';
                           //img1='Phonehandset.gif';
                    }
                  if(Number==address)
                        {

                                img1='Phonehandset.gif';
                                clearInterval(myinterval);

                        }
                  if(batterystatus==1)
                        {
                           img1='11.png';
                        }
 var marker = new google.maps.Marker({
            map: map,
            position: point,
            icon:img1,
            shadow: icon.shadow
          });
          bindInfoWindow(marker, map, infoWindow, html);
        }
      });
          }, 4000);

我的testing.php 文件输出如下:

<?xml version="1.0"?>
<ecb_config><marker Chainage="Police Bhavan,Vadodara" address="1005" status="1" lat="22.3016" lng="73.1933" temperkey="0" vibration="0" batterystatus="1"/><marker Chainage="" address="1001" status="1" lat="" lng="" temperkey="0" vibration="0" batterystatus="1"/><marker Chainage="20(Vadora)" address="1006" status="0" lat="18.35452552912664" lng="76.11328125" temperkey="0" vibration="0" batterystatus="0"/><marker Chainage="" address="1003" status="0" lat="" lng="" temperkey="" vibration="0" batterystatus=""/><marker Chainage="" address="1002" status="1" lat="18.5590" lng="73.7868" temperkey="0" vibration="0" batterystatus=""/></ecb_config>

在 google chrome 控制台中，出现以下错误。

NewPhone.php:4469 Uncaught TypeError: Cannot read property 'documentElement' of null
    at NewPhone.php:4469
    at XMLHttpRequest.request.onreadystatechange (NewPhone.php:4532)
(anonymous) @ NewPhone.php:4469
request.onreadystatechange @ NewPhone.php:4532
XMLHttpRequest.send (async)
downloadUrl @ NewPhone.php:4536
(anonymous) @ NewPhone.php:4466

Answer 1

首先尝试验证数据

if(xml.documentElement.nodeName!==null)