自定义配置文件读取

　　配置文件用处很多，最开始使用是在数据分页数量当中。其次接触是在NHibernate当中。抽象工厂+配置文件是一个很好的应用。通过接口+配置文件，可以很方便的实现开放封闭原则。

　　配置文件分为：元素，元素集合，节。

　　元素： 

public class PersistenceElement : ConfigurationElement
    {
        [ConfigurationProperty(ConfigName.PropertyName, IsKey = true, IsRequired = true)]
        public string EntityClass
        {
            get
            {
                return (string)this[ConfigName.PropertyName];
            }
            set
            {
                this[ConfigName.PropertyName] = value;
            }
        }

        [ConfigurationProperty(ConfigName.PropertyValue, IsRequired = true)]
        public string PersistenceClass
        {
            get
            {
                return (string)this[ConfigName.PropertyValue];
            }
            set
            {
                this[ConfigName.PropertyValue] = value;
            }
        }
    }

 　　元素集合：

public class PersistenceElementCollenction : ConfigurationElementCollection
    {
        protected override ConfigurationElement CreateNewElement()
        {
            return new PersistenceElement();
        }

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

        public override ConfigurationElementCollectionType CollectionType
        {
            get { return ConfigurationElementCollectionType.BasicMap; }
        }

        protected override string ElementName
        {
            get { return ConfigName.PersistenceElement; }
        }

        public PersistenceElement this[int index]
        {
            get { return (PersistenceElement)this.BaseGet(index); }
            set
            {
                if (this.BaseGet(index) != null)
                {
                    this.BaseRemoveAt(index);
                }
                this.BaseAdd(index, value);
            }
        }

        public new PersistenceElement this[string interfaceShortTypeName]
        {
            get { return (PersistenceElement)this.BaseGet(interfaceShortTypeName); }
        }

        public bool ContainsKey(string keyName)
        {
            bool result = false;
            object[] keys = this.BaseGetAllKeys();
            foreach (object key in keys)
            {
                if ((string)key == keyName)
                {
                    result = true;
                    break;

                }
            }
            return result;
        }
    }

　　节：

public class PersistenceProperty : ConfigurationSection
    {
        [ConfigurationProperty(ConfigName.PersistenceElementCollection,
           IsDefaultCollection = true)]
        public PersistenceElementCollenction GetElementCollection
        {
            get { return (PersistenceElementCollenction)base[ConfigName.PersistenceElementCollection]; }
        }
    }

　　配置文件的书写方式如下：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <section name="PersistenceSection" type="Configuration.PersistenceProperty, Configuration"/>
  </configSections>
  <PersistenceSection>
    <Persistences>
      <Persistence PropertyName="A1" PropertyValue="A1Factory"></Persistence>
      <Persistence PropertyName="A2" PropertyValue="A2Factory"></Persistence>
      <Persistence PropertyName="A3" PropertyValue="A3Factory"></Persistence>
    </Persistences>
  </PersistenceSection>
</configuration>

　　总结：通过配置文件我们可以动态的加载应用程序集。从而实现开放封闭原则。

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