Func<T1,T2,TResult> 代理人

定義

封裝具有兩個參數的方法,並傳回 TResult 參數所指定的型別值。Encapsulates a method that has two parameters and returns a value of the type specified by the TResult parameter.

generic <typename T1, typename T2, typename TResult>
public delegate TResult Func(T1 arg1, T2 arg2);
public delegate TResult Func<in T1,in T2,out TResult>(T1 arg1, T2 arg2);
type Func<'T1, 'T2, 'Result> = delegate of 'T1 * 'T2 -> 'Result
Public Delegate Function Func(Of In T1, In T2, Out TResult)(arg1 As T1, arg2 As T2) As TResult 

類型參數

T1

此委派封裝之方法的第一個參數類型。The type of the first parameter of the method that this delegate encapsulates.

這是反變數的型別參數。 也就是說,您可以使用您指定的類型,或衍生程度較低的任何類型。 如需共變數與反變數的詳細資訊,請參閱泛型中的共變數與反變數
T2

此委派封裝之方法的第二個參數類型。The type of the second parameter of the method that this delegate encapsulates.

這是反變數的型別參數。 也就是說,您可以使用您指定的類型,或衍生程度較低的任何類型。 如需共變數與反變數的詳細資訊,請參閱泛型中的共變數與反變數
TResult

這個委派所封裝之方法的傳回值之類型。The type of the return value of the method that this delegate encapsulates.

這是共變數的型別參數。 也就是說,您可以使用您指定的類型,或衍生程度較高的任何類型。 如需共變數與反變數的詳細資訊,請參閱泛型中的共變數與反變數

參數

arg1

此委派封裝之方法的第一個參數。The first parameter of the method that this delegate encapsulates.

arg2

此委派封裝之方法的第二個參數。The second parameter of the method that this delegate encapsulates.

傳回值

TResult

這個委派所封裝之方法的傳回值。The return value of the method that this delegate encapsulates.

繼承
Func<T1,T2,TResult>

範例

下列範例示範如何宣告和使用 Func<T1,T2,TResult> 委派。The following example demonstrates how to declare and use a Func<T1,T2,TResult> delegate. 這個範例會宣告 Func<T1,T2,TResult> 變數,並為其指派一個使用 String 值和 Int32 值做為參數的 lambda 運算式。This example declares a Func<T1,T2,TResult> variable and assigns it a lambda expression that takes a String value and an Int32 value as parameters. 如果 String 參數的長度等於 Int32 參數的值,則 lambda 運算式會傳回 trueThe lambda expression returns true if the length of the String parameter is equal to the value of the Int32 parameter. 接著會在查詢中使用封裝此方法的委派,以篩選字串陣列中的字串。The delegate that encapsulates this method is subsequently used in a query to filter strings in an array of strings.

using System;
using System.Collections.Generic;
using System.Linq;

public class Func3Example
{
   public static void Main()
   {
      Func<String, int, bool> predicate = (str, index) => str.Length == index;

      String[] words = { "orange", "apple", "Article", "elephant", "star", "and" };
      IEnumerable<String> aWords = words.Where(predicate).Select(str => str);

      foreach (String word in aWords)
         Console.WriteLine(word);
   }
}
Imports System.Collections.Generic
Imports System.Linq

Public Module Func3Example

   Public Sub Main()
      Dim predicate As Func(Of String, Integer, Boolean) = Function(str, index) str.Length = index

      Dim words() As String = { "orange", "apple", "Article", "elephant", "star", "and" }
      Dim aWords As IEnumerable(Of String) = words.Where(predicate)

      For Each word As String In aWords
         Console.WriteLine(word)
      Next   
   End Sub
End Module

備註

您可以使用這個委派來表示可當做參數傳遞的方法,而不需要明確宣告自訂委派。You can use this delegate to represent a method that can be passed as a parameter without explicitly declaring a custom delegate. 封裝的方法必須對應到此委派所定義的方法簽章。The encapsulated method must correspond to the method signature that is defined by this delegate. 這表示封裝的方法必須有兩個參數,其中每一個都會以傳值方式傳遞給它,而且它必須傳回值。This means that the encapsulated method must have two parameters, each of which is passed to it by value, and that it must return a value.

注意

若要參考具有兩個參數的方法,並傳回 void (或在 Visual Basic 中,宣告為 Sub 而不是 Function),請改用泛型 Action<T1,T2> 委派。To reference a method that has two parameters and returns void (or in Visual Basic, that is declared as a Sub rather than as a Function), use the generic Action<T1,T2> delegate instead.

當您使用 Func<T1,T2,TResult> 委派時,您不需要明確地定義委派,將具有兩個參數的方法封裝起來。When you use the Func<T1,T2,TResult> delegate you do not have to explicitly define a delegate that encapsulates a method with two parameters. 例如,下列程式碼會明確宣告名為 ExtractMethod 的委派,並將 ExtractWords 方法的參考指派給其委派實例。For example, the following code explicitly declares a delegate named ExtractMethod and assigns a reference to the ExtractWords method to its delegate instance.

using System;

delegate string[] ExtractMethod(string stringToManipulate, int maximum);

public class DelegateExample
{
   public static void Main()
   {
      // Instantiate delegate to reference ExtractWords method
      ExtractMethod extractMeth = ExtractWords;
      string title = "The Scarlet Letter";
      // Use delegate instance to call ExtractWords method and display result
      foreach (string word in extractMeth(title, 5))
         Console.WriteLine(word);
   }

   private static string[] ExtractWords(string phrase, int limit)
   {
      char[] delimiters = new char[] {' '};
      if (limit > 0)
         return phrase.Split(delimiters, limit);
      else
         return phrase.Split(delimiters);
   }
}
' Declare a delegate to represent string extraction method
Delegate Function ExtractMethod(ByVal stringToManipulate As String, _
                                ByVal maximum As Integer) As String()

Module DelegateExample
   Public Sub Main()
      ' Instantiate delegate to reference ExtractWords method
      Dim extractMeth As ExtractMethod = AddressOf ExtractWords
      Dim title As String = "The Scarlet Letter"
      ' Use delegate instance to call ExtractWords method and display result
      For Each word As String In extractMeth(title, 5)
         Console.WriteLine(word)
      Next   
   End Sub

   Private Function ExtractWords(phrase As String, limit As Integer) As String()
      Dim delimiters() As Char = {" "c}
      If limit > 0 Then
         Return phrase.Split(delimiters, limit)
      Else
         Return phrase.Split(delimiters)
      End If
   End Function
End Module

下列範例會藉由具現化 Func<T1,T2,TResult> 委派來簡化此程式碼,而不是明確定義新的委派,並將已命名的方法指派給它。The following example simplifies this code by instantiating a Func<T1,T2,TResult> delegate instead of explicitly defining a new delegate and assigning a named method to it.

using System;

public class GenericFunc
{
   public static void Main()
   {
      // Instantiate delegate to reference ExtractWords method
      Func<string, int, string[]> extractMethod = ExtractWords;
      string title = "The Scarlet Letter";
      // Use delegate instance to call ExtractWords method and display result
      foreach (string word in extractMethod(title, 5))
         Console.WriteLine(word);
   }

   private static string[] ExtractWords(string phrase, int limit)
   {
      char[] delimiters = new char[] {' '};
      if (limit > 0)
         return phrase.Split(delimiters, limit);
      else
         return phrase.Split(delimiters);
   }
}
Module GenericFunc
   Public Sub Main()
      ' Instantiate delegate to reference ExtractWords method
      Dim extractMeth As Func(Of String, Integer, String()) = AddressOf ExtractWords
      Dim title As String = "The Scarlet Letter"
      ' Use delegate instance to call ExtractWords method and display result
      For Each word As String In extractMeth(title, 5)
         Console.WriteLine(word)
      Next   
   End Sub

   Private Function ExtractWords(phrase As String, limit As Integer) As String()
      Dim delimiters() As Char = {" "c}
      If limit > 0 Then
         Return phrase.Split(delimiters, limit)
      Else
         Return phrase.Split(delimiters)
      End If
   End Function
End Module

您可以在中C#使用 Func<T1,T2,TResult> 委派與匿名方法,如下列範例所示。You can use the Func<T1,T2,TResult> delegate with anonymous methods in C#, as the following example illustrates. (如需匿名方法的簡介,請參閱匿名方法)。(For an introduction to anonymous methods, see Anonymous Methods.)

using System;

public class Anonymous
{
   public static void Main()
   {
      Func<string, int, string[]> extractMeth = delegate(string s, int i)
         { char[] delimiters = new char[] {' '}; 
           return i > 0 ? s.Split(delimiters, i) : s.Split(delimiters);
         };
      
      string title = "The Scarlet Letter";
      // Use Func instance to call ExtractWords method and display result
      foreach (string word in extractMeth(title, 5))
         Console.WriteLine(word);
   }
}

您也可以將 lambda 運算式指派給 Func<T1,T2,TResult> 委派,如下列範例所示。You can also assign a lambda expression to a Func<T1,T2,TResult> delegate, as the following example illustrates. (如需 lambda 運算式的簡介,請參閱Lambda 運算式lambda 運算式)。(For an introduction to lambda expressions, see Lambda Expressions and Lambda Expressions.)

using System;

public class LambdaExpression
{
   public static void Main()
   {
      char[] separators = new char[] {' '};
      Func<string, int, string[]> extract = (s, i) => 
           i > 0 ? s.Split(separators, i) : s.Split(separators) ;
         
      string title = "The Scarlet Letter";
      // Use Func instance to call ExtractWords method and display result
      foreach (string word in extract(title, 5))
         Console.WriteLine(word);
   }
}
Module LambdaExpression
   Public Sub Main()
      Dim separators() As Char = {" "c}
      Dim extract As Func(Of String, Integer, String()) = Function(s, i) _
          CType(iif(i > 0, s.Split(separators, i), s.Split(separators)), String())  
      
      Dim title As String = "The Scarlet Letter"
      For Each word As String In extract(title, 5)
         Console.WriteLine(word)
      Next   
   End Sub
End Module

Lambda 運算式的基礎類型是其中一個泛型 Func 委派。The underlying type of a lambda expression is one of the generic Func delegates. 如此一來,您就可以傳遞 lambda 運算式做為參數,而不需要明確地將它指派給委派。This makes it possible to pass a lambda expression as a parameter without explicitly assigning it to a delegate. 特別是,因為 System.Linq 命名空間中類型的許多方法都具有 Func<T1,T2,TResult> 參數,您可以將這些方法傳遞至 lambda 運算式,而不需要明確具現化 Func<T1,T2,TResult> 委派。In particular, because many methods of types in the System.Linq namespace have Func<T1,T2,TResult> parameters, you can pass these methods a lambda expression without explicitly instantiating a Func<T1,T2,TResult> delegate.

擴充方法

GetMethodInfo(Delegate)

取得表示特定委派所代表之方法的物件。Gets an object that represents the method represented by the specified delegate.

適用於

另請參閱