Action<T1,T2,T3> Delegate
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Encapsulates a method that has three parameters and does not return a value.
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)
Type Parameters
- T1
The type of the first parameter of the method that this delegate encapsulates.
This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.- T2
The type of the second parameter of the method that this delegate encapsulates.
This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.- T3
The type of the third parameter of the method that this delegate encapsulates.
This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.Parameters
- arg1
- T1
The first parameter of the method that this delegate encapsulates.
- arg2
- T2
The second parameter of the method that this delegate encapsulates.
- arg3
- T3
The third parameter of the method that this delegate encapsulates.
Remarks
You can use the Action<T1,T2,T3> delegate to pass a method as a parameter without explicitly declaring a custom delegate. The encapsulated method must correspond to the method signature that is defined by this delegate. This means that the encapsulated method must have three parameters that are all passed to it by value, and it must not return a value. (In C#, the method must return void
. In F#, the method or function must return unit. In Visual Basic, it must be defined by the Sub
…End Sub
construct. It can also be a method that returns a value that is ignored.) Typically, such a method is used to perform an operation.
Note
To reference a method that has three parameters and returns a value, use the generic Func<T1,T2,T3,TResult> delegate instead.
When you use the Action<T1,T2,T3> delegate, you don't have to explicitly define a delegate that encapsulates a method with three parameters. For example, the following code explicitly declares a delegate named StringCopy
and assigns a reference to the CopyStrings
method to its delegate instance.
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] = 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 RunIt()
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
If String.IsNullOrEmpty(ordinal) Then
Console.WriteLine("<None>")
Else
Console.WriteLine(ordinal)
End If
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) = source(ctr)
Next
End Sub
End Module
The following example simplifies this code by instantiating the Action<T1,T2,T3> delegate instead of explicitly defining a new delegate and assigning a named method to it.
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] = 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 RunIt()
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
If String.IsNullOrEmpty(ordinal) Then
Console.WriteLine("<None>")
Else
Console.WriteLine(ordinal)
End If
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) = source(ctr)
Next
End Sub
End Module
You can also use the Action<T1,T2,T3> delegate with anonymous methods in C#, as the following example illustrates. (For an introduction to anonymous methods, see 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] = source[ctr];
}
}
You can also assign a lambda expression to an Action<T1,T2,T3> delegate instance, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions (C#) or Lambda Expressions (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(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] = 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 RunIt()
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) = source(ctr)
Next
Return source.Length - startPos
End Function
End Module
' The example displays the following output:
' Fourth
' Fifth
Extension Methods
GetMethodInfo(Delegate) |
Gets an object that represents the method represented by the specified delegate. |
Applies to
See also
Povratne informacije
https://aka.ms/ContentUserFeedback.
Kmalu na voljo: V letu 2024 bomo ukinili storitev Težave v storitvi GitHub kot mehanizem za povratne informacije za vsebino in jo zamenjali z novim sistemom za povratne informacije. Za več informacij si oglejte:Pošlji in prikaži povratne informacije za