Action<T1,T2,T3> 委托

  • 参考

定义

命名空间:
System
程序集:
System.Runtime.dll
程序集:
System.Core.dll
程序集:
mscorlib.dll
程序集:
netstandard.dll

封装一个方法，该方法具有三个参数且不返回值。

generic <typename T1, typename T2, typename T3>
public delegate void Action(T1 arg1, T2 arg2, T3 arg3);
public delegate void Action<in T1,in T2,in T3>(T1 arg1, T2 arg2, T3 arg3);
public delegate void Action<T1,T2,T3>(T1 arg1, T2 arg2, T3 arg3);
type Action<'T1, 'T2, 'T3> = delegate of 'T1 * 'T2 * 'T3 -> unit
Public Delegate Sub Action(Of In T1, In T2, In T3)(arg1 As T1, arg2 As T2, arg3 As T3)
Public Delegate Sub Action(Of T1, T2, T3)(arg1 As T1, arg2 As T2, arg3 As T3)

类型参数

T1

此委托封装的方法的第一个参数的类型。

这是逆变类型参数。 即，可以使用指定的类型，也可以使用派生程度较低的任何类型。 有关协变和逆变的详细信息，请参阅泛型中的协变和逆变。
T2

此委托封装的方法的第二个参数的类型。

这是逆变类型参数。 即，可以使用指定的类型，也可以使用派生程度较低的任何类型。 有关协变和逆变的详细信息，请参阅泛型中的协变和逆变。
T3

此委托封装的方法的第三个参数的类型。

这是逆变类型参数。 即，可以使用指定的类型，也可以使用派生程度较低的任何类型。 有关协变和逆变的详细信息，请参阅泛型中的协变和逆变。

参数

arg1
T1

此委托封装的方法的第一个参数。

arg2
T2

此委托封装的方法的第二个参数。

arg3
T3

此委托封装的方法的第三个参数。

注解

可以使用 Action<T1,T2,T3> 委托将方法作为参数传递，而无需显式声明自定义委托。 封装的方法必须对应于此委托定义的方法签名。 这意味着封装的方法必须具有三个参数，这些参数都按值传递给它，并且不能返回值。 (在 C# 中，方法必须返回 void。在 F# 中，方法或函数必须返回 unit。在 Visual Basic 中，它必须由 ...End Sub 构造定义Sub。它也可以是返回忽略值的方法。) 通常，此类方法用于执行操作。

注意

若要引用具有三个参数并返回值的方法，请改用泛型 Func<T1,T2,T3,TResult> 委托。

使用 Action<T1,T2,T3> 委托时，不必显式定义一个委托，该委托封装具有三个参数的方法。 例如，以下代码显式声明名为 的 StringCopy 委托，并将对 方法的 CopyStrings 引用分配给其委托实例。

using System;

delegate void StringCopy(string[] stringArray1,
                         string[] stringArray2,
                         int indexToStart);

public class TestDelegate
{
   public static void Main()
   {
      string[] ordinals = {"First", "Second", "Third", "Fourth", "Fifth"};
      string[] copiedOrdinals = new string[ordinals.Length];
      StringCopy copyOperation = CopyStrings;
      copyOperation(ordinals, copiedOrdinals, 3);
      foreach (string ordinal in copiedOrdinals)
         Console.WriteLine(string.IsNullOrEmpty(ordinal) ? "<None>" : ordinal);
   }

   private static void CopyStrings(string[] source, string[] target, int startPos)
   {
      if (source.Length != target.Length)
         throw new IndexOutOfRangeException("The source and target arrays must have the same number of elements.");

      for (int ctr = startPos; ctr <= source.Length - 1; ctr++)
         target[ctr] = string.Copy(source[ctr]);
   }
}

open System

type StringCopy = delegate of stringArray1: string [] * 
                              stringArray2: string [] * 
                              indexToStart: int -> unit

let copyStrings (source: string []) (target: string []) startPos =
    if source.Length <> target.Length then
        raise (IndexOutOfRangeException "The source and target arrays must have the same number of elements.")

    for i = startPos to source.Length - 1 do
        target.[i] <- source.[i]

let ordinals = [| "First"; "Second"; "Third"; "Fourth"; "Fifth" |]
let copiedOrdinals: string [] = Array.zeroCreate ordinals.Length

let copyOperation = StringCopy copyStrings

copyOperation.Invoke(ordinals, copiedOrdinals, 3)

for ordinal in copiedOrdinals do
    printfn "%s" (if String.IsNullOrEmpty ordinal then "<None>" else ordinal)

Delegate Sub StringCopy(stringArray1() As String, _
                        stringArray2() As String, _
                        indexToStart As Integer)

Module TestDelegate
   Public Sub Main()
      Dim ordinals() As String = {"First", "Second", "Third", "Fourth", "Fifth"}
      Dim copiedOrdinals(ordinals.Length - 1) As String
      Dim copyOperation As StringCopy = AddressOf CopyStrings
      copyOperation(ordinals, copiedOrdinals, 3)
      For Each ordinal As String In copiedOrdinals
         Console.WriteLine(ordinal)
      Next    
   End Sub
   
   Private Sub CopyStrings(source() As String, target() As String, startPos As Integer)
      If source.Length <> target.Length Then 
         Throw New IndexOutOfRangeException("The source and target arrays must have the same number of elements.")
      End If
      For ctr As Integer = startPos to source.Length - 1
         target(ctr) = String.Copy(source(ctr))
      Next
   End Sub
End Module

以下示例通过实例化委托来简化此代码， Action<T1,T2,T3> 而不是显式定义新委托并为其分配命名方法。

using System;

public class TestAction3
{
   public static void Main()
   {
      string[] ordinals = {"First", "Second", "Third", "Fourth", "Fifth"};
      string[] copiedOrdinals = new string[ordinals.Length];
      Action<string[], string[], int> copyOperation = CopyStrings;
      copyOperation(ordinals, copiedOrdinals, 3);
      foreach (string ordinal in copiedOrdinals)
         Console.WriteLine(string.IsNullOrEmpty(ordinal) ? "<None>" : ordinal);
   }

   private static void CopyStrings(string[] source, string[] target, int startPos)
   {
      if (source.Length != target.Length)
         throw new IndexOutOfRangeException("The source and target arrays must have the same number of elements.");

      for (int ctr = startPos; ctr <= source.Length - 1; ctr++)
         target[ctr] = string.Copy(source[ctr]);
   }
}

open System

let copyStrings (source: string []) (target: string []) startPos =
    if source.Length <> target.Length then
        raise (IndexOutOfRangeException "The source and target arrays must have the same number of elements.")

    for i = startPos to source.Length - 1 do
        target.[i] <- source.[i]

let ordinals = [| "First"; "Second"; "Third"; "Fourth"; "Fifth" |]
let copiedOrdinals = Array.zeroCreate<string> ordinals.Length

let copyOperation = Action<_,_,_> copyStrings

copyOperation.Invoke(ordinals, copiedOrdinals, 3)

for ordinal in copiedOrdinals do
    printfn "%s" (if String.IsNullOrEmpty ordinal then "<None>" else ordinal)

Module TestAction3
   Public Sub Main()
      Dim ordinals() As String = {"First", "Second", "Third", "Fourth", "Fifth"}
      Dim copiedOrdinals(ordinals.Length - 1) As String
      Dim copyOperation As Action(Of String(), String(), Integer) = AddressOf CopyStrings
      copyOperation(ordinals, copiedOrdinals, 3)
      For Each ordinal As String In copiedOrdinals
         Console.WriteLine(ordinal)
      Next    
   End Sub
   
   Private Sub CopyStrings(source() As String, target() As String, startPos As Integer)
      If source.Length <> target.Length Then 
         Throw New IndexOutOfRangeException("The source and target arrays must have the same number of elements.")
      End If
      For ctr As Integer = startPos to source.Length - 1
         target(ctr) = String.Copy(source(ctr))
      Next
   End Sub
End Module

还可以在 C# 中将 Action<T1,T2,T3> 委托与匿名方法一起使用，如以下示例所示。 (有关匿名方法的简介，请参阅 Anonymous Methods.) 

using System;

public class TestAnon
{
   public static void Main()
   {
      string[] ordinals = {"First", "Second", "Third", "Fourth", "Fifth"};
      string[] copiedOrdinals = new string[ordinals.Length];
      Action<string[], string[], int> copyOperation = delegate(string[] s1,
                                                               string[] s2,
                                                               int pos)
                                      { CopyStrings(s1, s2, pos); };
      copyOperation(ordinals, copiedOrdinals, 3);
      foreach (string ordinal in copiedOrdinals)
         Console.WriteLine(string.IsNullOrEmpty(ordinal) ? "<None>" : ordinal);
   }

   private static void CopyStrings(string[] source, string[] target, int startPos)
   {
      if (source.Length != target.Length)
         throw new IndexOutOfRangeException("The source and target arrays must have the same number of elements.");

      for (int ctr = startPos; ctr <= source.Length - 1; ctr++)
         target[ctr] = string.Copy(source[ctr]);
   }
}

还可以将 lambda 表达式分配给 Action<T1,T2,T3> 委托实例，如以下示例所示。 (有关 lambda 表达式的简介，请参阅 Lambda 表达式 (C#) 或 lambda 表达式 (F#) .) 

using System;

public class TestLambda
{
   public static void Main()
   {
      string[] ordinals = {"First", "Second", "Third", "Fourth", "Fifth"};
      string[] copiedOrdinals = new string[ordinals.Length];
      Action<string[], string[], int> copyOperation = (s1, s2, pos) =>
                                      CopyStrings(s1, s2, pos);
      copyOperation(ordinals, copiedOrdinals, 3);
      foreach (string ordinal in copiedOrdinals)
         Console.WriteLine(ordinal == string.Empty ? "<None>" : ordinal);
   }

   private static void CopyStrings(string[] source, string[] target, int startPos)
   {
      if (source.Length != target.Length)
         throw new IndexOutOfRangeException("The source and target arrays must have the same number of elements.");

      for (int ctr = startPos; ctr <= source.Length - 1; ctr++)
         target[ctr] = string.Copy(source[ctr]);
   }
}

open System

let copyStrings (source: string []) (target: string []) startPos =
    if source.Length <> target.Length then
        raise (IndexOutOfRangeException "The source and target arrays must have the same number of elements.")

    for i = startPos to source.Length - 1 do
        target.[i] <- source.[i]

let ordinals = [| "First"; "Second"; "Third"; "Fourth"; "Fifth" |]
let copiedOrdinals: string [] = Array.zeroCreate ordinals.Length

let copyOperation = Action<_,_,_> (fun s1 s2 pos -> copyStrings s1 s2 pos)

copyOperation.Invoke(ordinals, copiedOrdinals, 3)

for ordinal in copiedOrdinals do
    printfn "%s" (if String.IsNullOrEmpty ordinal then "<None>" else ordinal)

Public Module TestLambda
   Public Sub Main()
      Dim ordinals() As String = {"First", "Second", "Third", "Fourth", "Fifth"}
      Dim copiedOrdinals(ordinals.Length - 1) As String           
      Dim copyOperation As Action(Of String(), String(), Integer) = _
                           Sub(s1, s2, pos) CopyStrings(s1, s2, pos) 
      copyOperation(ordinals, copiedOrdinals, 3)
      For Each ordinal As String In copiedOrdinals
         If String.IsNullOrEmpty(ordinal) Then
            Console.WriteLine("<None>")
         Else
            Console.WriteLine(ordinal)
         End If      
      Next   
   End Sub

   Private Function CopyStrings(source() As String, target() As String, startPos As Integer) As Integer
      If source.Length <> target.Length Then 
         Throw New IndexOutOfRangeException("The source and target arrays must have the same number of elements.")
      End If
      
      For ctr As Integer = startPos To source.Length - 1 
         target(ctr) = String.Copy(source(ctr))
      Next
      Return source.Length - startPos 
   End Function
End Module
' The example displays the following output:
'       Fourth
'       Fifth

扩展方法

GetMethodInfo(Delegate)

获取指示指定委托表示的方法的对象。

适用于

另请参阅