系统。NullReferenceException:对象引用未设置为对象的实例。系统。Xml。林克。XContainer。Elelement()返回null

我正在阅读从谷歌地球专业版保存的.kml文件。

这是我从SO上的一篇帖子中获得的代码。当xDoc运行时,它运行得很好。后代具有一致的元素。

    XDocument xDoc = XDocument.Load(openFileDialog1.FileName);
    XNamespace ns = "http://www.opengis.net/kml/2.2";

    var placemarks = xDoc.Descendants(ns + "Placemark").Select(p => new
        {
             Name = (string)p.Element(ns + "name").Value.ToString(),
             Coords = p.Element(ns + "Point").Element(ns + "coordinates").Value,
        })
        .ToArray();

这将产生以下公里数数据

image of form displaying the read KML elements

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2" xmlns:kml="http://www.opengis.net/kml/2.2" xmlns:atom="http://www.w3.org/2005/Atom">
<Document id="1Y-yAHoHb_KrjsRT70KM5qLdZQjN_xcKW">
    <name>Test kml</name>
    <Placemark id="0B2FCD3E802CFEB8E9AD">
        <name>0+00 cabinet location 12’ BOC</name>
        <LookAt>
            <longitude>-93.28687708665021</longitude>
            <latitude>44.84264135896755</latitude>
            <altitude>255.3402528075096</altitude>
            <heading>0</heading>
            <tilt>0</tilt>
            <range>36.48488765818456</range>
            <altitudeMode>absolute</altitudeMode>
            <gx:fovy>35</gx:fovy>
        </LookAt>
        <styleUrl>#msn_parking_lot</styleUrl>
        <Point>
            <coordinates>-93.28687708665021,44.84264135896755,255.3402528075096</coordinates>
        </Point>
    </Placemark>
    <Placemark>
        <name>Place HH</name>
        <LookAt>
            <longitude>-93.28692035131073</longitude>
            <latitude>44.84255178413457</latitude>
            <altitude>0</altitude>
            <heading>1.868100177527735e-05</heading>
            <tilt>15.19185305855737</tilt>
            <range>106.8343470069538</range>
            <gx:altitudeMode>relativeToSeaFloor</gx:altitudeMode>
        </LookAt>
        <styleUrl>#msn_square0</styleUrl>
        <Point>
            <gx:drawOrder>1</gx:drawOrder>
            <coordinates>-93.28690200178055,44.84263978936539,0</coordinates>
        </Point>
    </Placemark>
    <Placemark id="0C6BEBC5352CFEBCA94D">
        <name>0+45 sewer</name>
        <LookAt>
            <longitude>-93.28845935397412</longitude>
            <latitude>44.84257694352023</latitude>
            <altitude>251.8505380949421</altitude>
            <heading>0</heading>
            <tilt>0</tilt>
            <range>63.54447705992244</range>
            <altitudeMode>absolute</altitudeMode>
            <gx:fovy>35</gx:fovy>
        </LookAt>
        <styleUrl>#__managed_style_397C1C0EAA2D00EDBB6D</styleUrl>
        <Point>
            <coordinates>-93.28845935397412,44.84257694352023,251.8505380949421</coordinates>
        </Point>
    </Placemark>
</Document>
</kml>

但是当KML xDoc。后代有不一致的元素,如下面的KML,我得到了系统。Xml。林克。XContainer。Elelement()返回null错误,因为第一个位置标记没有point元素。

image of error in visual studio

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2" xmlns:kml="http://www.opengis.net/kml/2.2" xmlns:atom="http://www.w3.org/2005/Atom">
<Document id="1Y-yAHoHb_KrjsRT70KM5qLdZQjN_xcKW">
    <name>Test KML</name>
    <Placemark>
        <name>Running line</name>
        <styleUrl>#m_ylw-pushpin</styleUrl>
        <LineString>
            <tessellate>1</tessellate>
            <coordinates>
                -93.28762387862635,44.84811886228031,0 -93.28753369589279,44.84814969351044,0 -93.28751831971846,44.84825957026099,0 -93.28749752003094,44.84895772192719,0 
            </coordinates>
        </LineString>
    </Placemark>
    <Placemark>
        <name>Place HH</name>
        <LookAt>
            <longitude>-93.28692035131073</longitude>
            <latitude>44.84255178413457</latitude>
            <altitude>0</altitude>
            <heading>1.868100177527735e-05</heading>
            <tilt>15.19185305855737</tilt>
            <range>106.8343470069538</range>
            <gx:altitudeMode>relativeToSeaFloor</gx:altitudeMode>
        </LookAt>
        <styleUrl>#msn_square0</styleUrl>
        <Point>
            <gx:drawOrder>1</gx:drawOrder>
            <coordinates>-93.28690200178055,44.84263978936539,0</coordinates>
        </Point>
    </Placemark>
    <Placemark id="0C6BEBC5352CFEBCA94D">
        <name>0+45 sewer</name>
        <LookAt>
            <longitude>-93.28845935397412</longitude>
            <latitude>44.84257694352023</latitude>
            <altitude>251.8505380949421</altitude>
            <heading>0</heading>
            <tilt>0</tilt>
            <range>63.54447705992244</range>
            <altitudeMode>absolute</altitudeMode>
            <gx:fovy>35</gx:fovy>
        </LookAt>
        <styleUrl>#__managed_style_397C1C0EAA2D00EDBB6D</styleUrl>
        <Point>
            <coordinates>-93.28845935397412,44.84257694352023,251.8505380949421</coordinates>
        </Point>
    </Placemark>
</Document>
</kml>

有没有办法使用这种linq-select风格来处理不一致的元素?

最终,我希望当位置标记有坐标时,它能将坐标从linestring/coordinate元素中取出,当坐标在Point/coordination元素中时,它也能将坐标取出。我可以使用基于“子”元素的值或null填充多个数组值,而不会出现null错误吗?然后,我可以处理空值与值的关系。 如果点或线串中没有坐标,则两者都将为null,我将处理这个问题。