C#系统委托之Action And Func

时间：2014-12-02 22:15:25 阅读：323 评论：0 收藏：0 [点我收藏+]

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转自http://www.cnblogs.com/LittleFeiHu/p/4035166.html

Action：封装一个方法，该方法不具有参数并且不返回值

public delegate void Action()

Action<T>:Action的泛型实现了1到16个传入参数的定义，但是仍然没有返回值,得出结论Action不支持返回值，如果需要返回值请使用另一个系统委托Func

public delegate void Action<in T>(T obj)

...

public delegate void Action<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13, in T14, in T15, in T16>(

T1 arg1,

T2 arg2,

T3 arg3,

T4 arg4,

T5 arg5,

T6 arg6,

T7 arg7,

T8 arg8,

T9 arg9,

T10 arg10,

T11 arg11,

T12 arg12,

T13 arg13,

T14 arg14,

T15 arg15,

T16 arg16

)

由此可见Action的定义非常简单，但是这样的委托实在是太常用了，如果用一次自己定义一个也是可以的，多的话就感觉重复劳动太多：

过去自定义委托：

using System;
using System.Windows.Forms;

public delegate void ShowValue();

public class Name
{
   private string instanceName;

   public Name(string name)
   {
      this.instanceName = name;
   }

   public void DisplayToConsole()
   {
      Console.WriteLine(this.instanceName);
   }

   public void DisplayToWindow()
   {
      MessageBox.Show(this.instanceName);
   }
}

public class testTestDelegate
{
   public static void Main()
   {
      Name testName = new Name("Koani");
      ShowValue showMethod = testName.DisplayToWindow;
      showMethod();
   }
}

现在直接使用Action：

using System;
using System.Windows.Forms;

public class Name
{
   private string instanceName;

   public Name(string name)
   {
      this.instanceName = name;
   }

   public void DisplayToConsole()
   {
      Console.WriteLine(this.instanceName);
   }

   public void DisplayToWindow()
   {
      MessageBox.Show(this.instanceName);
   }
}

public class testTestDelegate
{
   public static void Main()
   {
      Name testName = new Name("Koani");
      Action showMethod = testName.DisplayToWindow;
      //将 Action 委托与匿名方法一起使用
     // Action showMethod = delegate() { testName.DisplayToWindow();} ;
      //将 lambda 表达式分配给 Action 委托实例
      //Action showMethod = () => testName.DisplayToWindow();
      showMethod();
   }
}

Action<T>的使用也是类似的，但是 Action<T>的定义是比较特别的，它有一个关键词In，In是用来干嘛的呢，按照MSDN的解释：

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Func:封装一个不具有参数但却返回 TResult 参数指定的类型值的方法

public delegate TResult Func<out TResult>()

Func<T>: Func的泛型同样的实现了1到16个传入参数，而且支持返回值。



public delegate TResult Func<in T, out TResult>(
    T arg
)
...
public delegate void Func<in T1, in T2, in T3, in T4, in T5, in T6, in T7, in T8, in T9, in T10, in T11, in T12, in T13, in T14, in T15, in T16, out TResult>(
    T1 arg1,
    T2 arg2,
    T3 arg3,
    T4 arg4,
    T5 arg5,
    T6 arg6,
    T7 arg7,
    T8 arg8,
    T9 arg9,
    T10 arg10,
    T11 arg11,
    T12 arg12,
    T13 arg13,
    T14 arg14,
    T15 arg15,
    T16 arg16
)