2. 工厂方法模式

定义一个用户创建对象的接口，让子类决定实例化哪一个类。使一个类的实例化延迟到其子类。 

工厂类与产品类往往具有平行的等级结构，它们之间一一对应。

 

相关类：

 1 namespace FactoryMethod
 2 {
 3 //日志
 4     public abstract class Log
 5     {
 6         public abstract void WriteLog();
 7     }
 8 //数据库日志
 9 public class DBLog : Log
10     {
11         public override void WriteLog()
12         {
13             Console.WriteLine("DBLog Success!");
14         }
15     }
16 //文本日志
17 public class TxtLog:Log
18     {
19         public override void WriteLog()
20         {
21             Console.WriteLine("TxtLog Success!");
22         }
23     }
24 //日志工厂
25 public abstract class LogFactory
26     {
27         public abstract Log CreateLog();
28     }
29 //数据库日志工厂
30 public class DBLogFactory:LogFactory
31     {
32         public override Log CreateLog()
33         {
34             return new DBLog();
35         }
36     }
37 //文本日志工厂
38 public class TxtLogFactory:LogFactory
39     {
40         public override Log CreateLog()
41         {
42             return new TxtLog();
43         }
44     }
45 //客户端
46 class Program
47     {
48         static void Main(string[] args)
49         {
50             string assembly = ConfigurationManager.AppSettings["Assembly"];
51             string instance = ConfigurationManager.AppSettings["Instance"];
52             //应用反射来创建工厂，在更换工厂时，不需要修改代码
53             LogFactory factory = (LogFactory)Assembly.Load(assembly).
54                 CreateInstance(instance);
55             Log log = factory.CreateLog();
56             log.WriteLog();
57             Console.ReadLine();
58         }
59     }
60 }

app.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="Assembly" value="FactoryMethod"/>
    <add key="Instance" value="FactoryMethod.DBLogFactory"/>
  </appSettings>
</configuration>