Action<T1,T2,T3> 委托
定义
重要
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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
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
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