c# - 在使用 linqtoxml 分配之前如何检查元素的值不为空

Question

我正在使用 linq to xml 使用下面的代码从 xml 输入中读取值

var values = xDoc.Descendants("result").Select(c =>
                     new
                     {
                         FullAddress = c.Element("formatted_address").Value,

                          CountryName = c.Descendants("address_component")
                         .First(e => e.Element("type").Value == "country").Element("long_name").Value,

                         CountryNameCode = c.Descendants("address_component")
                         .First(e => e.Element("type").Value == "country").Element("short_name").Value,

                         CityName = c.Descendants("address_component")
                                 .First(e => e.Element("type").Value == "locality").Element("short_name").Value,


                     }).First();

我们如何检查xml输入中某个元素的值是否存在并且不为空，例如

 CityName = c.Descendants("address_component").First(e => e.Element("type").Value =="locality").Element("short_name").Value

我的输入 xml 是

<?xml version="1.0" encoding="UTF-8"?>
<GeocodeResponse>
<status>OK</status>
<result>
    <type>postal_code</type>
    <formatted_address>Inverclyde PA16 0XN, UK</formatted_address>
    <address_component>
        <long_name>PA16 0XN</long_name>
        <short_name>PA16 0XN</short_name>
        <type>postal_code</type>
    </address_component>
    <address_component>
        <long_name>Inverclyde</long_name>
        <short_name>Inverclyde</short_name>
        <type>administrative_area_level_2</type>
        <type>political</type>
    </address_component>
    <address_component>
        <long_name>United Kingdom</long_name>
        <short_name>GB</short_name>
        <type>country</type>
        <type>political</type>
    </address_component>
    <geometry>
        <location>
            <lat>55.9437962</lat>
            <lng>-4.8097700</lng>
        </location>
        <location_type>APPROXIMATE</location_type>
        <viewport>
            <southwest>
                <lat>55.9426062</lat>
                <lng>-4.8127289</lng>
            </southwest>
            <northeast>
                <lat>55.9453041</lat>
                <lng>-4.8075776</lng>
            </northeast>
        </viewport>
        <bounds>
            <southwest>
                <lat>55.9428874</lat>
                <lng>-4.8127289</lng>
            </southwest>
            <northeast>
                <lat>55.9450229</lat>
                <lng>-4.8075776</lng>
            </northeast>
        </bounds>
    </geometry>
</result>
</GeocodeResponse>

Answer 1

我认为扩展方法将是处理此问题的好方法。这将需要一些检查，因为有很多时候值可能为空，但这应该涵盖您的用例。

void Main()
{
    var doc = XDocument.Load(@"C:\Test\test.xml");

    var city = doc.Descendants("address_component").FirstOrDefault(e => e.Element("type") != null 
                            && e.Element("type").Value =="locality");

    if(city != null){                       
     Console.WriteLine (city.GetElementIfExists("short_name"));
    } else {
     Console.WriteLine ("No short name found");
    }
}

public static class Extensions {
 public static string GetElementIfExists(this XElement @this, string element){
   return @this.Element(element) != null ? @this.Element(element).Value : String.Empty;
 }
}