Func<T1,T2,TResult> Delegate

Definition

Incapsula un metodo che presenta due parametri e restituisce un valore del tipo specificato dal parametro TResult.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);
public delegate TResult Func<T1,T2,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 
Public Delegate Function Func(Of T1, T2, TResult)(arg1 As T1, arg2 As T2) As TResult 

Type Parameters

T1

Tipo del primo parametro del metodo incapsulato da questo delegato.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

Tipo del secondo parametro del metodo incapsulato da questo delegato.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.
TResult

Tipo del valore restituito del metodo incapsulato da questo delegato.The type of the return value of the method that this delegate encapsulates.

This type parameter is covariant. That is, you can use either the type you specified or any type that is more derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.

Parameters

arg1
T1

Primo parametro del metodo incapsulato da questo delegato.The first parameter of the method that this delegate encapsulates.

arg2
T2

Secondo parametro del metodo incapsulato da questo delegato.The second parameter of the method that this delegate encapsulates.

Return Value

TResult

Valore restituito del metodo incapsulato da questo delegato.The return value of the method that this delegate encapsulates.

Inheritance
Func<T1,T2,TResult>

Examples

Nell'esempio seguente viene illustrato come dichiarare e utilizzare un delegato Func<T1,T2,TResult>.The following example demonstrates how to declare and use a Func<T1,T2,TResult> delegate. In questo esempio viene dichiarata una variabile di Func<T1,T2,TResult> e viene assegnata un'espressione lambda che accetta un valore String e un valore Int32 come parametri.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. L'espressione lambda restituisce true se la lunghezza del parametro String è uguale al valore del parametro Int32.The lambda expression returns true if the length of the String parameter is equal to the value of the Int32 parameter. Il delegato che incapsula questo metodo viene successivamente utilizzato in una query per filtrare le stringhe in una matrice di stringhe.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

Remarks

È possibile utilizzare questo delegato per rappresentare un metodo che può essere passato come parametro senza dichiarare in modo esplicito un delegato personalizzato.You can use this delegate to represent a method that can be passed as a parameter without explicitly declaring a custom delegate. Il metodo incapsulato deve corrispondere alla firma del metodo definita da questo delegato.The encapsulated method must correspond to the method signature that is defined by this delegate. Questo significa che il metodo incapsulato deve avere due parametri, ognuno dei quali viene passato in base al valore e che deve restituire un valore.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.

Note

Per fare riferimento a un metodo che presenta due parametri e restituisce void (o in Visual Basic, dichiarato come Sub anziché come Function), usare invece il delegato di Action<T1,T2> generico.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.

Quando si usa il delegato Func<T1,T2,TResult> non è necessario definire in modo esplicito un delegato che incapsula un metodo con due parametri.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. Il codice seguente, ad esempio, dichiara in modo esplicito un delegato denominato ExtractMethod e assegna un riferimento al metodo ExtractWords alla relativa istanza del delegato.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

Nell'esempio seguente viene semplificato questo codice creando un'istanza di un delegato Func<T1,T2,TResult> anziché definire in modo esplicito un nuovo delegato e assegnarvi un metodo denominato.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

È possibile usare il delegato Func<T1,T2,TResult> con i metodi anonimi in C#, come illustrato nell'esempio seguente.You can use the Func<T1,T2,TResult> delegate with anonymous methods in C#, as the following example illustrates. Per un'introduzione ai metodi anonimi, vedere metodi anonimi.(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);
   }
}

È anche possibile assegnare un'espressione lambda a un delegato Func<T1,T2,TResult>, come illustrato nell'esempio seguente.You can also assign a lambda expression to a Func<T1,T2,TResult> delegate, as the following example illustrates. Per un'introduzione alle espressioni lambda, vedere espressioni lambda ed espressioni lambda.(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

Il tipo sottostante di un'espressione lambda è uno dei delegati di Func generici.The underlying type of a lambda expression is one of the generic Func delegates. Ciò consente di passare un'espressione lambda come parametro senza assegnarla in modo esplicito a un delegato.This makes it possible to pass a lambda expression as a parameter without explicitly assigning it to a delegate. In particolare, poiché molti metodi dei tipi nello spazio dei nomi System.Linq hanno parametri Func<T1,T2,TResult>, è possibile passare a un'espressione lambda questi metodi senza creare un'istanza esplicita di un delegato Func<T1,T2,TResult>.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.

Extension Methods

GetMethodInfo(Delegate)

Ottiene un oggetto che rappresenta il metodo rappresentato dal delegato specificato.Gets an object that represents the method represented by the specified delegate.

Applies to

See also