Func<T1,T2,TResult> Delegate

Definition

封装一个方法,该方法具有两个参数,并返回由 TResult 参数指定的类型的值。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);
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

此委托封装的方法的第一个参数的类型。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

此委托封装的方法的第二个参数的类型。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

此委托封装的方法的返回值类型。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

此委托封装的方法的第一个参数。The first parameter of the method that this delegate encapsulates.

arg2
T2

此委托封装的方法的第二个参数。The second parameter of the method that this delegate encapsulates.

Return Value

TResult

此委托封装的方法的返回值。The return value of the method that this delegate encapsulates.

Inheritance
Func<T1,T2,TResult>

Examples

下面的示例演示如何声明和使用 Func<T1,T2,TResult> 委托。The following example demonstrates how to declare and use a Func<T1,T2,TResult> delegate. 此示例声明一个 Func<T1,T2,TResult> 变量,并为其分配一个 lambda 表达式,该表达式采用 String 值和 Int32 值作为参数。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 参数的长度等于 Int32 参数的值,则 lambda 表达式将返回 trueThe lambda expression returns true if the length of the String parameter is equal to the value of the Int32 parameter. 随后在查询中使用封装此方法的委托来筛选字符串数组中的字符串。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

Remarks

您可以使用此委托来表示一个方法,该方法可作为参数传递,而无需显式声明自定义委托。You can use this delegate to represent a method that can be passed as a parameter without explicitly declaring a custom delegate. 封装的方法必须对应于由此委托定义的方法签名。The encapsulated method must correspond to the method signature that is defined by this delegate. 这意味着,封装的方法必须具有两个参数,每个参数都按值传递到该方法,并且必须返回一个值。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.

Note

若要引用一个方法,该方法具有两个参数并返回 void (或者在 Visual Basic 中,该方法被声明为 Sub 而不是 Function),请改用泛型 Action<T1,T2> 委托。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.

使用 Func<T1,T2,TResult> 委托时,无需显式定义一个委托,该委托封装具有两个参数的方法。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,下面的代码显式声明名为 ExtractMethod 的委托,并向其委托实例分配对 ExtractWords 方法的引用。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

下面的示例通过实例化 Func<T1,T2,TResult> 委托简化了此代码,而不是显式定义新委托并为其分配命名方法。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

可以在中C#使用匿名方法的 Func<T1,T2,TResult> 委托,如下面的示例所示。You can use the Func<T1,T2,TResult> delegate with anonymous methods in C#, as the following example illustrates. (有关匿名方法的介绍,请参阅匿名方法。)(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);
   }
}

你还可以将 lambda 表达式分配给 Func<T1,T2,TResult> 委托,如下面的示例所示。You can also assign a lambda expression to a Func<T1,T2,TResult> delegate, as the following example illustrates. (有关 lambda 表达式的介绍,请参阅Lambda 表达式lambda 表达式。)(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 表达式的基础类型是泛型 Func 委托之一。The underlying type of a lambda expression is one of the generic Func delegates. 这样,便可以将 lambda 表达式作为参数传递,而无需将其显式分配给委托。This makes it possible to pass a lambda expression as a parameter without explicitly assigning it to a delegate. 具体来说,因为 System.Linq 命名空间中的许多类型的方法都具有 Func<T1,T2,TResult> 参数,所以可以将这些方法传递给 lambda 表达式,而无需显式实例化 Func<T1,T2,TResult> 委托。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)

获取指示指定委托表示的方法的对象。Gets an object that represents the method represented by the specified delegate.

Applies to

See also