C#系统委托之Action And Func

  1. Action
  2. Action<T>
  3. Func
  4. Func<T>

 

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();
   }
}
View Code

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();
   }
}
View Code

  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
)

 

Func的定义同样简单明了，和Action一样是为了简化代码方便”客户“使用：

过去自定义委托：

using System;
using System.IO;

delegate bool WriteMethod();

public class TestDelegate
{
   public static void Main()
   {
      OutputTarget output = new OutputTarget();
      WriteMethod methodCall = output.SendToFile;
      if (methodCall())
         Console.WriteLine("Success!"); 
      else
         Console.WriteLine("File write operation failed.");
   }
}

public class OutputTarget
{
   public bool SendToFile()
   {
      try
      {
         string fn = Path.GetTempFileName();
         StreamWriter sw = new StreamWriter(fn);
         sw.WriteLine("Hello, World!");
         sw.Close();
         return true;
      }  
      catch
      {
         return false;
      }
   }
}
View Code

 

现在直接使用Func：

using System;
using System.IO;

public class TestDelegate
{
   public static void Main()
   {
      OutputTarget output = new OutputTarget();
      Func<bool> methodCall = output.SendToFile;
     //Func<bool> methodCall = delegate() { return output.SendToFile(); };将 Func<TResult> 委托与匿名方法一起使用
     // Func<bool> methodCall = () => output.SendToFile(); 将 lambda 表达式分配给 Func<T, TResult> 委托
      if (methodCall())
         Console.WriteLine("Success!"); 
      else
         Console.WriteLine("File write operation failed.");
   }
}

public class OutputTarget
{
   public bool SendToFile()
   {
      try
      {
         string fn = Path.GetTempFileName();
         StreamWriter sw = new StreamWriter(fn);
         sw.WriteLine("Hello, World!");
         sw.Close();
         return true;
      }  
      catch
      {
         return false;
      }
   }
}
View Code

 

 

通过定义可以看到Func的定义不仅可以看到In关键词的身影，还有一个Out关键词，MSDN的解释如下（Out作为方法的输出参数也是经常用到的）：

 

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;

namespace CLR
{
    public class Employee
    {

    }
    class Program
    {
        static void Main(string[] args)
        {
            Employee emp = new Employee();
            object obj = emp;

            IList<Employee> emplist = new List<Employee>();

            // List<object> objlist = emplist;

            IList<object> objlist1 = emplist.Select(o => (object)o).ToList(); ;
            //因为Ilist的泛型参数T没有使用Out关键词标识，所以在给方法Add1直接传递 IList<Employee>类型的参数时会有无效参数提示
            Add1(emplist);
            //间接的使用方法是像上面那样逐个转换
            Add1(objlist1);


            IEnumerable<Employee> empenum = new List<Employee>();
            IEnumerable<object> objenum = empenum;

            Add(empenum);
            Add(objenum);

            Console.ReadKey();
        }
        private static void Add(IEnumerable<object> enums)
        {

        }

        private static void Add1(IList<object> enums)
        {

        }
    }
}

 

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posted @ 2014-10-19 17:46  麻将我会  阅读(3675)  评论(2)  编辑  收藏  举报