ConfigurationSection类（.Net）难度

Question

我很难使这个ConfigurationSection实现工作。这里的目标是为MIME文件类型提供可配置的文件扩展名映射。我按照两个教程试图达到这个设计，从来没有工作过。我怀疑是因为电话ConfigurationManager.GetSection("extensionFiletypes") as FilenameExtensionTypeConfiguration返回null。我做错了什么，如何解决？

的App.config

<configuration>
    <configSections>
        <section name="extensionFiletypes" type="Models.Config.FilenameExtensionTypeConfiguration, Models.Config"/>
    </configSections>
    <extensionFiletypes>
        <collection>
            <add extension="acx" type="application/internet-property-stream" />
            <add extension="ai" type="application/postscript" />
            ...
            <add extension="z" type="application/x-compress" />
            <add extension="zip" type="application/zip" />
        </collection>
    </extensionFiletypes>
</configuration>

类：

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

namespace Models.Config
{
    public sealed class FilenameExtensionTypeConfiguration : ConfigurationSection
    {
        public static FilenameExtensionTypeConfiguration GetConfiguration()
        {
            var configuration = ConfigurationManager.GetSection("extensionFiletypes") as FilenameExtensionTypeConfiguration;
            return configuration ?? new FilenameExtensionTypeConfiguration();
        }

    ...
}