Question

配置如下

<MyCollection default="one">
  <entry name="one" ... other attrubutes />
  ... other entries
</MyCollection>

实现MyCollection时，我该怎么做“默认”属性？

Answer 1

假设你有这个.config文件：

<configuration>
    <configSections>
        <section name="mySection" type="ConsoleApplication1.MySection, ConsoleApplication1" /> // update type  & assembly names accordingly
    </configSections>

    <mySection>
        <MyCollection default="one">
            <entry name="one" />
            <entry name="two" />
        </MyCollection>
    </mySection>
</configuration>

然后，使用此代码：

public class MySection : ConfigurationSection
{
    [ConfigurationProperty("MyCollection", Options = ConfigurationPropertyOptions.IsRequired)]
    public MyCollection MyCollection
    {
        get
        {
            return (MyCollection)this["MyCollection"];
        }
    }
}

[ConfigurationCollection(typeof(EntryElement), AddItemName = "entry", CollectionType = ConfigurationElementCollectionType.BasicMap)]
public class MyCollection : ConfigurationElementCollection
{
    protected override ConfigurationElement CreateNewElement()
    {
        return new EntryElement();
    }

    protected override object GetElementKey(ConfigurationElement element)
    {
        if (element == null)
            throw new ArgumentNullException("element");

        return ((EntryElement)element).Name;
    }

    [ConfigurationProperty("default", IsRequired = false)]
    public string Default
    {
        get
        {
            return (string)base["default"];
        }
    }
}

public class EntryElement : ConfigurationElement
{
    [ConfigurationProperty("name", IsRequired = true, IsKey = true)]
    public string Name
    {
        get
        {
            return (string)base["name"];
        }
    }
}

您可以使用'default'属性读取配置，如下所示：

    MySection section = (MySection)ConfigurationManager.GetSection("mySection");
    Console.WriteLine(section.MyCollection.Default);

这将输出“one”

Answer 2

我不知道ConfigurationElementCollection中是否可以有一个默认值。（它没有看到默认值的任何属性）。

我猜你必须自己实现这个。请看下面的例子。

public class Repository : ConfigurationElement
{
    [ConfigurationProperty("key", IsRequired = true)]
    public string Key
    {
        get { return (string)this["key"]; }
    }

    [ConfigurationProperty("value", IsRequired = true)]
    public string Value
    {
        get { return (string)this["value"]; }
    }
}

public class RepositoryCollection : ConfigurationElementCollection
{
    protected override ConfigurationElement CreateNewElement()
    {
        return new Repository();
    }

    protected override object GetElementKey(ConfigurationElement element)
    {
        return (element as Repository).Key;
    }

    public Repository this[int index]
    {
        get { return base.BaseGet(index) as Repository; }
    }

    public new Repository this[string key]
    {
        get { return base.BaseGet(key) as Repository; }
    }

}

public class MyConfig : ConfigurationSection
{
    [ConfigurationProperty("currentRepository", IsRequired = true)]
    private string InternalCurrentRepository
    {
        get { return (string)this["currentRepository"]; }
    }

    [ConfigurationProperty("repositories", IsRequired = true)]
    private RepositoryCollection InternalRepositories
    {
        get { return this["repositories"] as RepositoryCollection; }
    }
}

这是XML配置：

  <myConfig currentRepository="SQL2008">
    <repositories>
      <add key="SQL2008" value="abc"/>
      <add key="Oracle" value="xyz"/>
    </repositories>
  </myConfig>

然后，在您的代码中，您使用以下内容访问默认项目：

MyConfig conf = (MyConfig)ConfigurationManager.GetSection("myConfig");
string myValue = conf.Repositories[conf.CurrentRepository].Value;

当然，MyConfig类可以隐藏访问Repositories和CurrentRepository属性的详细信息。你可以在MyConfig类中有一个名为DefaultRepository（类型为Repository）的属性来返回它。

Answer 3

这可能有点晚，但可能对其他人有帮助。

这是可能的，但有一些修改。

ConfigurationElementCollection继承ConfigurationElement，因为“this [string]”在ConfigurationElement中可用。
通常当ConfigurationElementCollection在另一个类中继承并实现时，“this [string]”隐藏为“new this [string]”。
解决它的一种方法是创建此[]的另一个实现，例如“this [string，string]”

见下面的例子。

public class CustomCollection : ConfigurationElementCollection
{
    protected override ConfigurationElement CreateNewElement()
    {
        return new CustomElement();
    }

    protected override object GetElementKey(ConfigurationElement element)
    {
        return ((CustomElement)element).Name;
    }

    public CustomElement this[int index]
    {
        get { return (CustomElement)base.BaseGet(index); }
        set
        {
            if (BaseGet(index) != null)
                BaseRemoveAt(index);

            BaseAdd(index, value);
        }
    }

    // ConfigurationElement this[string] now becomes hidden in child class
    public new CustomElement this[string name]
    {
        get { return (CustomElement)BaseGet(name); }
    }

    // ConfigurationElement this[string] is now exposed
    // however, a value must be entered in second argument for property to be access
    // otherwise "this[string]" will be called and a CustomElement returned instead
    public object this[string name, string str = null]
    {
        get { return base[name]; }
        set { base[name] = value; }
    }
}

Answer 4

如果你想对它进行泛化，这应该会有所帮助：

using System.Configuration;

namespace Abcd
{
  // Generic implementation of ConfigurationElementCollection.
  [ConfigurationCollection(typeof(ConfigurationElement))]
  public class ConfigurationElementCollection<T> : ConfigurationElementCollection
                                         where T : ConfigurationElement, IConfigurationElement, new()
  {
    protected override ConfigurationElement CreateNewElement()
    {
      return new T();
    }

    protected override object GetElementKey(ConfigurationElement element)
    {
      return ((IConfigurationElement)element).GetElementKey();
    }

    public T this[int index]
    {
      get { return (T)BaseGet(index); }
    }

    public T GetElement(object key)
    {
      return (T)BaseGet(key);
    }
  }
}

以下是上面引用的界面：

namespace Abcd
{
  public interface IConfigurationElement
  {
    object GetElementKey();
  }
}

如何在ConfigurationElementCollection中拥有自定义属性？

4 个答案: