二十四种设计模式：外观模式(Facade Pattern)

外观模式(Facade Pattern)

介绍
为子系统中的一组接口提供一个一致的界面，Facade模式定义了一个高层接口，这个接口使得这一子系统更加容易使用。

示例
有一个Message实体类，某对象对它的操作有Get()方法，另外还有一个对象有一个Validate()方法来判断用户是否有权限。现在提供一个高层接口来封装这两个方法。

　　MessageModel

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Facade
{
    /// <summary>
    /// Message实体类
    /// </summary>
    public class MessageModel
    {
        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="msg">Message内容</param>
        /// <param name="pt">Message发布时间</param>
        public MessageModel(string msg, DateTime pt)
        {
            this._message = msg;
            this._publishTime = pt;
        }

        private string _message;
        /// <summary>
        /// Message内容
        /// </summary>
        public string Message
        {
            get { return _message; }
            set { _message = value; }
        }

        private DateTime _publishTime;
        /// <summary>
        /// Message发布时间
        /// </summary>
        public DateTime PublishTime
        {
            get { return _publishTime; }
            set { _publishTime = value; }
        }
    }
}

　　User

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Facade
{
    /// <summary>
    /// 用户相关类
    /// </summary>
    public class User
    {
        /// <summary>
        /// 验证用户是否合法
        /// </summary>
        /// <param name="userId">UserId</param>
        /// <returns></returns>
        public bool Validate(string userId)
        {
            if (userId == "admin")
            {
                return true;
            }
            else
            {
                return false;
            }
        }
    }
}

　　SqlMessage

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Facade
{
    /// <summary>
    /// Sql方式操作Message
    /// </summary>
    public class SqlMessage
    {
        /// <summary>
        /// 获取Message
        /// </summary>
        /// <returns></returns>
        public List<MessageModel> Get()
        {
            List<MessageModel> l = new List<MessageModel>();
            l.Add(new MessageModel("SQL方式获取Message", DateTime.Now));

            return l;
        }
    }
}

　　Message

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Facade
{
    /// <summary>
    /// Facade类
    /// </summary>
    public class Message
    {
        private string _userId = "";

        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="userId">UserId</param>
        public Message(string userId)
        {
            this._userId = userId;
        }

        /// <summary>
        /// 获取Message
        /// 首先使用User类的Validate()方法验证用户是否合法
        /// 然后使用SqlMessage类的Get()方法获取Message
        /// </summary>
        /// <returns></returns>
        public List<MessageModel> Get()
        {
            User u = new User();
            SqlMessage m = new SqlMessage();

            if (u.Validate(_userId))
            {
                return m.Get();
            }
            else
            {
                List<MessageModel> l = new List<MessageModel>();
                l.Add(new MessageModel("无权获取", DateTime.Now));

                return l;
            }
        }
    }
}

　　Client

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

using Pattern.Facade;

public partial class Facade : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Message m = new Message("user");
        Response.Write(m.Get()[0].Message + " " + m.Get()[0].PublishTime.ToString());
        Response.Write("<br />");

        m = new Message("admin");
        Response.Write(m.Get()[0].Message + " " + m.Get()[0].PublishTime.ToString());
        Response.Write("<br />");
    }
}

　　运行结果
　　无权获取 2007-3-20 22:16:50
　　SQL方式获取Message 2007-3-20 22:16:50