结论

• 如果不创建自定义属性类，则不支持属性集集合。
• 支持创建自定义属性类是非常好的。
• 创建自定义属性类的文档是糟糕的，但是我终于找到了一个体面的概述文档，帮助我找到了答案。

配置文件

我最终得到的app.config文件是:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <configSections>
        <sectionGroup name="userSettings" 
                      type="System.Configuration.UserSettingsGroup, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" >
            <section name="executiveBranch" 
                     type="PropProto.Properties.ExecutiveBranchSection, PropProto, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" 
                     allowExeDefinition="MachineToLocalUser" 
                     requirePermission="false" />
        </sectionGroup>
    </configSections>
    <userSettings>
        <executiveBranch>
            <presidents>
                <president key="first"
                           name="George Washington"
                           legacy="The Fother of Our County"
                           />
                <president key="honestAbe"
                           name="Abraham Lincoln"
                           legacy="Freed the Slaves"
                           />
                <president key="who"
                           name="Chester Arthur"
                           />
                <president key="dubya"
                           name="George W. Bush"
                           legacy="Mission Accomplished!!!"
                           />
                <president key="barack"
                           name="Barack Obama"
                           legacy="Affordable Health Care"
                           />
            </presidents>
        </executiveBranch>
    </userSettings>
</configuration>

比我预期的(或想要的)多了一个嵌套层。这是因为presidents是ConfigurationElementCollection，而userSettings不能直接包含ConfigurationElementCollection，所以我不得不引入executiveBranch。

使用配置

var exeConfiguration = ConfigurationManager.OpenExeConfiguration(
      ConfigurationUserLevel.PerUserRoamingAndLocal);
var userSettings = exeConfiguration.GetSectionGroup("userSettings");
var executiveBranch = (ExecutiveBranchSection)userSettings.Sections.Get(
        ExecutiveBranchSection.Tag);
var presidents = executiveBranch.Presidents;
foreach (President president in presidents)
{
    Console.WriteLine("{0}: {1}", president.Name, president.Legacy);
}

自定义属性类

和使这一切工作的自定义类:

public class ExecutiveBranchSection : ConfigurationSection
{
    public const string Tag = "executiveBranch";
    [ConfigurationProperty(PresidentCollection.Tag)]
    public PresidentCollection Presidents { get { return (PresidentCollection)base[PresidentCollection.Tag]; } }
}
[ConfigurationCollection(typeof(President),
    CollectionType = ConfigurationElementCollectionType.BasicMap,
    AddItemName = President.Tag)]
public class PresidentCollection : ConfigurationElementCollection
{
    public const string Tag = "presidents";
    protected override string ElementName { get { return President.Tag; } }
    public President this[int index]
    {
        get { return (President)base.BaseGet(index); }
        set
        {
            if (base.BaseGet(index) != null)
            {
                base.BaseRemoveAt(index);
            }
            base.BaseAdd(index, value);
        }
    }
    new public President this[string name] { get { return (President)base.BaseGet(name); } }
    protected override ConfigurationElement CreateNewElement()
    {
        return new President();
    }
    protected override object GetElementKey(ConfigurationElement element)
    {
        return (element as President).Key;
    }
}
public class President : ConfigurationElement
{
    public const string Tag = "president";
    [ConfigurationProperty("key", IsRequired = true)]
    public string Key { get { return (string)base["key"]; } }
    [ConfigurationProperty("name", IsRequired = true)]
    public string Name { get { return (string)base["name"]; } }
    [ConfigurationProperty("legacy", IsRequired = false)]
    public string Legacy { get { return (string)base["legacy"]; } }
}

没有使用自定义配置部分，但从纯逻辑的角度来看，这不是更合适吗:

<userSettings>
    <servers>
        <add name="washington" host="abc.presidents.com" port="1414" credentials="george"/>
        <add name="adams" host="def.presidents.com" port="1419" credentials="john"/>
        <!--insert more server definitions here -->
    </servers>
    <!-- insert more user settings here -->
</userSettings>

你可以用其他的方法，但是如果你想要一个"server"的集合，那么它必须在一个分组元素中，比如"servers"。不能在父元素中只包含多个"server"，而父元素还可以包含其他类型的子元素。组内的标签几乎都是"add"

在任何情况下"System.Configuration. "SingleTagSectionHandler"绝对不是正确的类型。