明确实现接口时装箱的成本是多少

显式成员实施的当前指导原则建议:

使用显式成员来近似私有接口实现.如果您只是出于基础架构原因需要实现接口,并且您从不希望开发人员直接从该类型调用该接口上的方法,那么明确地实现成员以从公共视图中"隐藏"它们.

公开一种替代方法来访问允许子类重写的任何显式实现的成员.

一个很好的例子就是你想要实现IXmlSerializable接口.该的ReadXml和中WriteXML有望方法由XmlSerializer的调用,而不是通常由开发商直接调用.

当提供一种替代方法来明确访问您希望允许被覆盖的成员时,调用显式实现的成员似乎是有意义的,以避免代码重复.考虑以下:

using System;
using System.Xml;
using System.Xml.Schema;
using System.Xml.Serialization;

namespace Demo
{
    /// 

    /// Demonstrates explicit implementation of the IXmlSerializable interface.
    /// 
    [Serializable(), XmlRoot(ElementName = "foo")]
    public class Foo : IXmlSerializable
    {
        //============================================================
        //  IXmlSerializable Implementation
        //============================================================
        #region GetSchema()
        /// 

        /// Returns an  that describes the XML representation of the object.
        /// 
        /// 
        /// An  that describes the XML representation of the object that is 
        /// produced by the  method and consumed by the  method.
        /// 
        /// This method is reserved and should not be used.
        XmlSchema IXmlSerializable.GetSchema()
        {
            return null;
        }
        #endregion

        #region ReadXml(XmlReader reader)
        /// 

        /// Generates an object from its XML representation.
        /// 
        /// The  stream from which the object is deserialized.
        /// The  is a null reference (Nothing in Visual Basic).
        void IXmlSerializable.ReadXml(XmlReader reader)
        {
            // Class state values read from supplied XmlReader
        }
        #endregion

        #region WriteXml(XmlWriter writer)
        /// 

        /// Converts an object into its XML representation.
        /// 
        /// The  stream to which the object is serialized.
        /// The  is a null reference (Nothing in Visual Basic).
        void IXmlSerializable.WriteXml(XmlWriter writer)
        {
            // Current class state values written using supplied XmlWriter
        }
        #endregion

        //============================================================
        //  Public Methods
        //============================================================
        #region WriteTo(XmlWriter writer)
        /// 

        /// Saves the current  to the specified .
        /// 
        /// The  stream to which the  is serialized.
        /// The  is a null reference (Nothing in Visual Basic).
        public void WriteTo(XmlWriter writer)
        {
            writer.WriteStartElement("foo");

            ((IXmlSerializable)this).WriteXml(writer);

            writer.WriteEndElement();
        }
        #endregion
    }
}

我的问题是关于WriteXml方法在此实现中的装箱有多昂贵.是((IXmlSerializable)这个.).WriteXml(作家)会显着阻碍性能？

在你的例子中没有拳击......它只是一个演员,它在编译时可以解析,因此它根本不会对性能产生任何影响.

编辑:使用ILDASM查看它,接口强制转换将为您提供虚拟方法调用与常规方法调用,但这可以忽略不计(仍然没有涉及到拳击).

编辑2:如果您使用结构而不是类,那么您将获得一个通过界面的框,更多的性能损失.