Action<T1,T2> 委托
重要
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封装一个方法,该方法具有两个参数且不返回值。
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);
public delegate void Action<T1,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)
Public Delegate Sub Action(Of T1, T2)(arg1 As T1, arg2 As T2)
- 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。
可以使用 Action<T1,T2> 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两个参数,两个参数均按值传递给它,并且不能返回值。 (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
若要引用具有两个参数并返回值的方法,请改用泛型 Func<T1,T2,TResult> 委托。
使用 Action<T1,T2> 委托时,无需显式定义封装具有两个参数的方法的委托。 例如,以下代码显式声明名为 ConcatStrings
.. 然后,它将对两个方法之一的引用分配给其委托实例。 一种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。
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();
}
}
}
open System
open System.IO
type ConcatStrings = delegate of string1: string * string1: string -> unit
let message1 = "The first line of a message"
let message2 = "The second line of a message"
let writeToConsole string1 string2 =
printfn $"{string1}\n{string2}"
let writeToFile string1 string2 =
use writer = new StreamWriter(Environment.GetCommandLineArgs().[1], false)
writer.WriteLine $"{string1}\n{string2}"
let concat =
ConcatStrings(fun string1 string2 ->
if Environment.GetCommandLineArgs().Length > 1 then
writeToFile string1 string2
else
writeToConsole string1 string2
)
concat.Invoke(message1, message2)
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
以下示例通过实例化 Action<T1,T2> 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;
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();
}
}
}
open System
open System.IO
let message1 = "The first line of a message"
let message2 = "The second line of a message"
let writeToConsole string1 string2 =
printfn $"{string1}\n{string2}"
let writeToFile string1 string2 =
use writer = new StreamWriter(Environment.GetCommandLineArgs().[1], false)
writer.WriteLine $"{string1}\n{string2}"
let concat =
Action<string, string>(fun string1 string2 ->
if Environment.GetCommandLineArgs().Length > 1 then
writeToFile string1 string2
else
writeToConsole string1 string2
)
concat.Invoke(message1, message2)
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
还可以将 Action<T1,T2> 委托与 C# 中的匿名方法配合使用,如以下示例所示。 (有关匿名方法简介,请参阅 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();
}
}
}
还可以将 lambda 表达式分配给 Action<T1,T2> 委托实例,如以下示例所示。 (有关 lambda 表达式简介,请参阅 lambda 表达式 (C#) ,或 lambda 表达式 (F#) .)
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();
}
}
}
open System
open System.IO
let message1 = "The first line of a message"
let message2 = "The second line of a message"
let writeToConsole string1 string2 =
printfn $"{string1}\n{string2}"
let writeToFile string1 string2 =
use writer = new StreamWriter(Environment.GetCommandLineArgs().[1], false)
writer.WriteLine $"{string1}\n{string2}"
let concat =
Action<string,string>(
if Environment.GetCommandLineArgs().Length > 1 then
fun s1 s2 -> writeToFile s1 s2
else
fun s1 s2 -> writeToConsole s1 s2
)
concat.Invoke(message1, message2)
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
Get |
获取指示指定委托表示的方法的对象。 |