如何识别丢失的ConfigurationElement？

Question

使用System.Configuration，如何识别一个子配置元素是否完全丢失，或者仅仅是空的？

测试程序

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MissingConfigElementTest
{
    class MyConfigurationElement : ConfigurationElement
    {
        [ConfigurationProperty("name")]
        public string Name
        {
            get { return (string)base["name"]; }
        }
    }

    class MyConfigurationSection : ConfigurationSection
    {
        [ConfigurationProperty("empty", DefaultValue = null)]
        public MyConfigurationElement Empty
        {
            get { return (MyConfigurationElement)base["empty"]; }
        }

        [ConfigurationProperty("missing", DefaultValue = null)]
        public MyConfigurationElement Missing
        {
            get { return (MyConfigurationElement)base["missing"]; }
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var configSection = (MyConfigurationSection)ConfigurationManager.GetSection("mySection");

            Console.WriteLine("Empty.Name: " + (configSection.Empty.Name ?? "<NULL>"));
            Console.WriteLine("Missing.Name: " + (configSection.Missing.Name ?? "<NULL>"));

            Console.ReadLine();
        }
    }
}

测试配置

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <section name="mySection" type="MissingConfigElementTest.MyConfigurationSection, MissingConfigElementTest"/>
  </configSections>
  <mySection>
    <empty />
  </mySection>
</configuration>

输出

输出是

Empty.Name: 
Missing.Name:

问题

我找不到一种方法来区分空的，但是现在的配置元素和整个配置元素被忽略的情况。

我想要这样做，因为如果存在一个元素，我希望确保它通过了某些验证逻辑，但也可以完全排除元素。

Answer 1

您可以搜索以下部分：

var sections = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None).Sections;
var exists = sections.Cast<ConfigurationSection>()
                .Any(x => x.SectionInformation.Type.StartsWith("MissingConfigElementTest.MyConfigurationSection"));

Answer 2

为此，可以使用ElementInformation.IsPresent属性来确定元素是否存在于原始配置中。

var configSection = ( MyConfigurationSection ) ConfigurationManager.GetSection( "mySection" );

Console.WriteLine( "Empty.Name: " + ( configSection.Empty.ElementInformation.IsPresent ? configSection.Empty.Name : "<NULL>" ) );
Console.WriteLine( "Missing.Name: " + ( configSection.Missing.ElementInformation.IsPresent ? configSection.Missing.Name : "<NULL>" ) );

Console.ReadLine( );

这将输出

Empty.Name:
Missing.Name: <NULL>