Action<T1,T2> 委托

定义

封装一个方法,该方法具有两个参数且不返回值。Encapsulates a method that has two parameters and does not return a value.

generic <typename T1, typename T2>
public delegate void Action(T1 arg1, T2 arg2);
public delegate void Action<in T1,in T2>(T1 arg1, T2 arg2);
type Action<'T1, 'T2> = delegate of 'T1 * 'T2 -> unit
Public Delegate Sub Action(Of In T1, In T2)(arg1 As T1, arg2 As T2)

类型参数

T1

此委托封装的方法的第一个参数的类型。The type of the first parameter of the method that this delegate encapsulates.

T2

此委托封装的方法的第二个参数的类型。The type of the second parameter of the method that this delegate encapsulates.

参数

arg1

此委托封装的方法的第一个参数。The first parameter of the method that this delegate encapsulates.

arg2

此委托封装的方法的第二个参数。The second parameter of the method that this delegate encapsulates.

继承
Action<T1,T2>

注解

可以使用Action<T1,T2>委托以参数形式传递方法, 而无需显式声明自定义委托。You can use the Action<T1,T2> delegate to pass a method as a parameter without explicitly declaring a custom delegate. 封装的方法必须对应于由此委托定义的方法签名。The encapsulated method must correspond to the method signature that is defined by this delegate. 这意味着封装的方法必须具有两个通过值传递给它的参数, 并且不能返回值。This means that the encapsulated method must have two parameters that are both passed to it by value, and it must not return a value. (在C#中, 该方法必须void返回。(In C#, the method must return void. 在 Visual Basic 中, 它必须由Sub...End SubIn Visual Basic, it must be defined by the SubEnd Sub 构造.construct. 它也可以是返回忽略的值的方法。)通常, 这种方法用于执行操作。It can also be a method that returns a value that is ignored.) Typically, such a method is used to perform an operation.

备注

若要引用具有两个参数并返回值的方法, 请改用泛型Func<T1,T2,TResult>委托。To reference a method that has two parameters and returns a value, use the generic Func<T1,T2,TResult> delegate instead.

使用Action<T1,T2>委托时, 无需显式定义一个委托, 该委托封装带有两个参数的方法。When you use the Action<T1,T2> delegate, you do not have to explicitly define a delegate that encapsulates a method with two parameters. 例如, 下面的代码显式声明一个名为ConcatStrings的委托。For example, the following code explicitly declares a delegate named ConcatStrings. 然后, 它将对两个方法之一的引用分配给它的委托实例。It then assigns a reference to either of two methods to its delegate instance. 一个方法将两个字符串写入控制台;第二个字符串将两个字符串写入文件。One method writes two strings to the console; the second writes two strings to a file.

using System;
using System.IO;

delegate void ConcatStrings(string string1, string string2);

public class TestDelegate
{
   public static void Main()
   {
      string message1 = "The first line of a message.";
      string message2 = "The second line of a message.";
      ConcatStrings concat;
      
      if (Environment.GetCommandLineArgs().Length > 1)
         concat = WriteToFile;
      else
         concat = WriteToConsole;
         
      concat(message1, message2);
   }
  
   private static void WriteToConsole(string string1, string string2)
   {
      Console.WriteLine("{0}\n{1}", string1, string2);            
   }

   private static void WriteToFile(string string1, string string2)
   {
      StreamWriter writer = null;  
      try
      {
         writer = new StreamWriter(Environment.GetCommandLineArgs()[1], false);
         writer.WriteLine("{0}\n{1}", string1, string2);
      }
      catch
      {
         Console.WriteLine("File write operation failed...");
      }
      finally
      {
         if (writer != null) writer.Close();
      }      
   }
}
Imports System.IO

Delegate Sub ConcatStrings(string1 As String, string2 As String)

Module TestDelegate
   Public Sub Main()
      
      Dim message1 As String = "The first line of a message."
      Dim message2 As String = "The second line of a message."
      Dim concat As ConcatStrings
      
      If Environment.GetCommandLineArgs().Length > 1 Then
         concat = AddressOf WriteToFile
      Else
         concat = AddressOf WriteToConsole
      End If   
      concat(message1, message2)         
   End Sub
   
   Private Sub WriteToConsole(string1 As String, string2 As String)
      Console.WriteLine("{0}{1}{2}", string1, vbCrLf, string2)
   End Sub
   
   Private Sub WriteToFile(string1 As String, string2 As String)
      Dim writer As StreamWriter = Nothing  
      Try
         writer = New StreamWriter(Environment.GetCommandLineArgs(1), False)
         writer.WriteLine("{0}{1}{2}", string1, vbCrLf, string2)
      Catch
         Console.WriteLine("File write operation failed...")
      Finally
         If writer IsNot Nothing Then writer.Close
      End Try      
   End Sub
End Module

下面的示例通过实例化Action<T1,T2>委托来简化此代码, 而不是显式定义一个新委托并为其分配一个命名方法。The following example simplifies this code by instantiating the Action<T1,T2> delegate instead of explicitly defining a new delegate and assigning a named method to it.

using System;
using System.IO;

public class TestAction2
{
   public static void Main()
   {
      string message1 = "The first line of a message.";
      string message2 = "The second line of a message.";
      Action<string, string> concat;
      
      if (Environment.GetCommandLineArgs().Length > 1)
         concat = WriteToFile;
      else
         concat = WriteToConsole;
         
      concat(message1, message2);
   }
  
   private static void WriteToConsole(string string1, string string2)
   {
      Console.WriteLine("{0}\n{1}", string1, string2);            
   }

   private static void WriteToFile(string string1, string string2)
   {
      StreamWriter writer = null;  
      try
      {
         writer = new StreamWriter(Environment.GetCommandLineArgs()[1], false);
         writer.WriteLine("{0}\n{1}", string1, string2);
      }
      catch
      {
         Console.WriteLine("File write operation failed...");
      }
      finally
      {
         if (writer != null) writer.Close();
      }      
   }
}
Imports System.IO

Module TestAction2
   Public Sub Main()
      
      Dim message1 As String = "The first line of a message."
      Dim message2 As String = "The second line of a message."
      Dim concat As Action(Of String, String)
      
      If Environment.GetCommandLineArgs().Length > 1 Then
         concat = AddressOf WriteToFile
      Else
         concat = AddressOf WriteToConsole
      End If   
      concat(message1, message2)         
   End Sub
   
   Private Sub WriteToConsole(string1 As String, string2 As String)
      Console.WriteLine("{0}{1}{2}", string1, vbCrLf, string2)
   End Sub
   
   Private Sub WriteToFile(string1 As String, string2 As String)
      Dim writer As StreamWriter = Nothing  
      Try
         writer = New StreamWriter(Environment.GetCommandLineArgs(1), False)
         writer.WriteLine("{0}{1}{2}", string1, vbCrLf, string2)
      Catch
         Console.WriteLine("File write operation failed...")
      Finally
         If writer IsNot Nothing Then writer.Close
      End Try      
   End Sub
End Module

你还可以在中Action<T1,T2> C#将委托与匿名方法一起使用, 如下面的示例所示。You can also use the Action<T1,T2> delegate with anonymous methods in C#, as the following example illustrates. (有关匿名方法的介绍, 请参阅匿名方法。)(For an introduction to anonymous methods, see Anonymous Methods.)

using System;
using System.IO;

public class TestAnonymousMethod
{
   public static void Main()
   {
      string message1 = "The first line of a message.";
      string message2 = "The second line of a message.";
      Action<string, string> concat;
      
      if (Environment.GetCommandLineArgs().Length > 1)
         concat = delegate(string s1, string s2) { WriteToFile(s1, s2); };
      else
         concat = delegate(string s1, string s2) { WriteToConsole(s1, s2);} ;
         
      concat(message1, message2);
   }
  
   private static void WriteToConsole(string string1, string string2)
   {
      Console.WriteLine("{0}\n{1}", string1, string2);            
   }

   private static void WriteToFile(string string1, string string2)
   {
      StreamWriter writer = null;  
      try
      {
         writer = new StreamWriter(Environment.GetCommandLineArgs()[1], false);
         writer.WriteLine("{0}\n{1}", string1, string2);
      }
      catch
      {
         Console.WriteLine("File write operation failed...");
      }
      finally
      {
         if (writer != null) writer.Close();
      }      
   }
}

你还可以将 lambda 表达式分配给Action<T1,T2>委托实例, 如下面的示例所示。You can also assign a lambda expression to an Action<T1,T2> delegate instance, as the following example illustrates. (有关 lambda 表达式的介绍, 请参阅Lambda 表达式。)(For an introduction to lambda expressions, see Lambda Expressions.)

using System;
using System.IO;

public class TestLambdaExpression
{
   public static void Main()
   {
      string message1 = "The first line of a message.";
      string message2 = "The second line of a message.";
      Action<string, string> concat;
      
      if (Environment.GetCommandLineArgs().Length > 1)
         concat = (s1, s2) => WriteToFile(s1, s2);
      else
         concat = (s1, s2) => WriteToConsole(s1, s2);
         
      concat(message1, message2);
   }
  
   private static void WriteToConsole(string string1, string string2)
   {
      Console.WriteLine("{0}\n{1}", string1, string2);            
   }

   private static void WriteToFile(string string1, string string2)
   {
      StreamWriter writer = null;  
      try
      {
         writer = new StreamWriter(Environment.GetCommandLineArgs()[1], false);
         writer.WriteLine("{0}\n{1}", string1, string2);
      }
      catch
      {
         Console.WriteLine("File write operation failed...");
      }
      finally
      {
         if (writer != null) writer.Close();
      }      
   }
}
Imports System.IO

Public Module TestLambdaExpression

   Public Sub Main()
      Dim message1 As String = "The first line of a message."
      Dim message2 As String = "The second line of a message."
      Dim concat As Action(Of String, String)
      
      If Environment.GetCommandLineArgs().Length > 1 Then
         concat = Sub(s1, s2) WriteToFile(s1, s2)
      Else
         concat = Sub(s1, s2) WriteToConsole(s1, s2)
      End If
         
      concat(message1, message2)
   End Sub
  
   Private Function WriteToConsole(string1 As String, string2 As String) As Integer
      Dim message As String = String.Format("{0}{1}{2}", string1, vbCrLf, string2)
      Console.WriteLine(message)
      Return message.Length
   End Function

   Private Function WriteToFile(string1 As String, string2 As String) As Integer
      Dim writer As StreamWriter = Nothing  
      Dim message As String = String.Format("{0}{1}{2}", string1, vbCrLf, string2)
      Dim charsWritten As Integer
      Try
         writer = New StreamWriter(Environment.GetCommandLineArgs()(1), False)
         writer.WriteLine(message)
      Catch
         Console.WriteLine("File write operation failed...")
      Finally
         If writer IsNot Nothing Then 
            writer.Close()
            charsWritten = message.Length
         Else
            charsWritten = 0
         End If
      End Try      
      Return charsWritten
   End Function
End Module

扩展方法

GetMethodInfo(Delegate)

获取指示指定委托表示的方法的对象。Gets an object that represents the method represented by the specified delegate.

适用于

另请参阅