Action<T1,T2,T3,T4> 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

重要

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封装一个方法，该方法具有四个参数且不返回值。

generic <typename T1, typename T2, typename T3, typename T4>
public delegate void Action(T1 arg1, T2 arg2, T3 arg3, T4 arg4);

public delegate void Action<in T1,in T2,in T3,in T4>(T1 arg1, T2 arg2, T3 arg3, T4 arg4);

public delegate void Action<T1,T2,T3,T4>(T1 arg1, T2 arg2, T3 arg3, T4 arg4);

type Action<'T1, 'T2, 'T3, 'T4> = delegate of 'T1 * 'T2 * 'T3 * 'T4 -> unit

Public Delegate Sub Action(Of In T1, In T2, In T3, In T4)(arg1 As T1, arg2 As T2, arg3 As T3, arg4 As T4)

Public Delegate Sub Action(Of T1, T2, T3, T4)(arg1 As T1, arg2 As T2, arg3 As T3, arg4 As T4)

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。

T4

此委托封装的方法的第四个参数的类型。

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。

arg4: T4

此委托封装的方法的第四个参数。

注解

可以使用 Action<T1,T2,T3,T4> 委托将方法作为参数传递，而无需显式声明自定义委托。封装的方法必须与此委托定义的方法签名相对应。这意味着封装方法必须具有四个参数，这些参数全部通过值传递给它，并且不能返回值。 (在 C# 中，该方法必须返回 void。在 F# 中，方法或函数必须返回单位。在Visual Basic中，它必须由 ... 定义Sub``End Sub construct。它也可以是返回忽略的值的方法。) 通常，此类方法用于执行操作。

备注

若要引用具有四个参数并返回值的方法，请改用泛型 Func<T1,T2,T3,T4,TResult> 委托。

使用 Action<T1,T2,T3,T4> 委托时，无需显式定义封装具有四个参数的方法的委托。例如，以下代码显式声明命名 StringCopy 的委托，并向委托实例分配对 CopyStrings 方法的引用。

using System;

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

public class TestDelegate
{
   public static void Main()
   {
      string[] ordinals = {"First", "Second", "Third", "Fourth", "Fifth",
                           "Sixth", "Seventh", "Eighth", "Ninth", "Tenth"};
      string[] copiedOrdinals = new string[ordinals.Length];
      StringCopy copyOperation = CopyStrings;
      copyOperation(ordinals, copiedOrdinals, 3, 5);
      foreach (string ordinal in copiedOrdinals)
         Console.WriteLine(string.IsNullOrEmpty(ordinal) ? "<None>" : ordinal);
   }

   private static void CopyStrings(string[] source, string[] target,
                                   int startPos, int number)
   {
      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 <= startPos + number - 1; ctr++)
         target[ctr] = string.Copy(source[ctr]);
   }
}

open System

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

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

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

let ordinals =
    [| "First"; "Second"; "Third"; "Fourth"; "Fifth"
       "Sixth"; "Seventh"; "Eighth"; "Ninth"; "Tenth" |]

let copiedOrdinals: string [] = Array.zeroCreate ordinals.Length

let copyOperation = StringCopy copyStrings

copyOperation.Invoke(ordinals, copiedOrdinals, 3, 5)

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, _
                        numberToCopy As Integer)

Module TestDelegate
   Public Sub Main()
      Dim ordinals() As String = {"First", "Second", "Third", "Fourth", _
                                  "Fifth", "Sixth", "Seventh", "Eighth", _
                                  "Ninth", "Tenth"}
      Dim copiedOrdinals(ordinals.Length - 1) As String
      Dim copyOperation As StringCopy = AddressOf CopyStrings
      copyOperation(ordinals, copiedOrdinals, 3, 5)
      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, number 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 startpos + number  - 1
         target(ctr) = String.Copy(source(ctr))
      Next
   End Sub
End Module

以下示例通过实例化 Action<T1,T2,T3,T4> 委托而不是显式定义新委托并向其分配命名方法来简化此代码。

using System;

public class TestAction4
{
   public static void Main()
   {
      string[] ordinals = {"First", "Second", "Third", "Fourth", "Fifth",
                           "Sixth", "Seventh", "Eighth", "Ninth", "Tenth"};
      string[] copiedOrdinals = new string[ordinals.Length];
      Action<string[], string[], int, int> copyOperation = CopyStrings;
      copyOperation(ordinals, copiedOrdinals, 3, 5);
      foreach (string ordinal in copiedOrdinals)
         Console.WriteLine(string.IsNullOrEmpty(ordinal) ? "<None>" : ordinal);
   }

   private static void CopyStrings(string[] source, string[] target,
                                   int startPos, int number)
   {
      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 <= startPos + number - 1; ctr++)
         target[ctr] = string.Copy(source[ctr]);
   }
}

open System

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

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

let ordinals =
    [| "First"; "Second"; "Third"; "Fourth"; "Fifth"
       "Sixth"; "Seventh"; "Eighth"; "Ninth"; "Tenth" |]

let copiedOrdinals: string [] = Array.zeroCreate ordinals.Length

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

copyOperation.Invoke(ordinals, copiedOrdinals, 3, 5)

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

Module TestAction4
   Public Sub Main()
      Dim ordinals() As String = {"First", "Second", "Third", "Fourth", _
                                  "Fifth", "Sixth", "Seventh", "Eighth", _
                                  "Ninth", "Tenth"}
      Dim copiedOrdinals(ordinals.Length - 1) As String
      Dim copyOperation As Action(Of String(), String(), Integer, Integer) = _
                           AddressOf CopyStrings
      copyOperation(ordinals, copiedOrdinals, 3, 5)
      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, number 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 startpos + number  - 1
         target(ctr) = String.Copy(source(ctr))
      Next
   End Sub
End Module

还可以将 Action<T1,T2,T3,T4> 委托与 C# 中的匿名方法一起使用，如以下示例所示。 (有关匿名方法简介，请参阅 Anonymous Methods.)

using System;

public class TestAnonymousMethod
{
   public static void Main()
   {
      string[] ordinals = {"First", "Second", "Third", "Fourth", "Fifth",
                           "Sixth", "Seventh", "Eighth", "Ninth", "Tenth"};
      string[] copiedOrdinals = new string[ordinals.Length];
      Action<string[], string[], int, int> copyOperation =
                                           delegate(string[] s1, string[] s2,
                                           int pos, int num)
                                { CopyStrings(s1, s2, pos, num); };
      copyOperation(ordinals, copiedOrdinals, 3, 5);
      foreach (string ordinal in copiedOrdinals)
         Console.WriteLine(string.IsNullOrEmpty(ordinal) ? "<None>" : ordinal);
   }

   private static void CopyStrings(string[] source, string[] target,
                                   int startPos, int number)
   {
      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 <= startPos + number - 1; ctr++)
         target[ctr] = string.Copy(source[ctr]);
   }
}

还可以将 lambda 表达式分配给 Action<T1,T2,T3,T4> 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 TestLambdaExpression
{
   public static void Main()
   {
      string[] ordinals = {"First", "Second", "Third", "Fourth", "Fifth",
                           "Sixth", "Seventh", "Eighth", "Ninth", "Tenth"};
      string[] copiedOrdinals = new string[ordinals.Length];
      Action<string[], string[], int, int> copyOperation = (s1, s2, pos, num)
                                           => CopyStrings(s1, s2, pos, num);
      copyOperation(ordinals, copiedOrdinals, 3, 5);
      foreach (string ordinal in copiedOrdinals)
         Console.WriteLine(string.IsNullOrEmpty(ordinal) ? "<None>" : ordinal);
   }

   private static void CopyStrings(string[] source, string[] target,
                                   int startPos, int number)
   {
      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 <= startPos + number - 1; ctr++)
         target[ctr] = string.Copy(source[ctr]);
   }
}

open System

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

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

let ordinals =
    [| "First"; "Second"; "Third"; "Fourth"; "Fifth"
       "Sixth"; "Seventh"; "Eighth"; "Ninth"; "Tenth" |]

let copiedOrdinals: string [] = Array.zeroCreate ordinals.Length

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

copyOperation.Invoke(ordinals, copiedOrdinals, 3, 5)

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

Public Module TestLambdaExpression
   Public Sub Main()
      Dim ordinals() As String = {"First", "Second", "Third", "Fourth", "Fifth", _ 
                           "Sixth", "Seventh", "Eighth", "Ninth", "Tenth"}
      Dim copiedOrdinals(ordinals.Length - 1) As String           
      Dim copyOperation As Action(Of String(), String(), Integer, Integer) = _
                           Sub(s1, s2, pos, num) CopyStrings(s1, s2, pos, num)  
      copyOperation(ordinals, copiedOrdinals, 3, 5)
      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, number 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 startPos + number - 1
         target(ctr) = String.Copy(source(ctr))
      Next
      Return number
   End Function
End Module
' The example displays the following output:
'       Fourth
'       Fifth
'       Sixth
'       Seventh
'       Eighth

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

Func<T1,T2,T3,T4,TResult>

通过

Action<T1,T2,T3,T4> 委托

定义

类型参数

参数

注解

扩展方法

适用于

另请参阅

其他资源