Func<T,TResult> Func<T,TResult> Func<T,TResult> Func<T,TResult> Delegate

定义

封装一个具有一个参数并返回 TResult 参数指定的类型值的方法。Encapsulates a method that has one parameter and returns a value of the type specified by the TResult parameter.

generic <typename T, typename TResult>
public delegate TResult Func(T arg);
public delegate TResult Func<in T,out TResult>(T arg);
type Func<'T, 'Result> = delegate of 'T -> 'Result
Public Delegate Function Func(Of In T, Out TResult)(arg As T) As TResult 

类型参数

T

此委托封装的方法的参数类型。The type of the parameter of the method that this delegate encapsulates.

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.

参数

arg

此委托封装的方法的参数。The parameter of the method that this delegate encapsulates.

返回值

TResult

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

继承
Func<T,TResult>Func<T,TResult>Func<T,TResult>Func<T,TResult>

示例

下面的示例演示如何声明和使用Func<T,TResult>委托。The following example demonstrates how to declare and use a Func<T,TResult> delegate. 此示例声明Func<T,TResult>变量并将其分配将在字符串中的字符转换为大写的 lambda 表达式。This example declares a Func<T,TResult> variable and assigns it a lambda expression that converts the characters in a string to uppercase. 此委托封装此方法随后传递给Enumerable.Select方法更改为大写的字符串数组中的字符串。The delegate that encapsulates this method is subsequently passed to the Enumerable.Select method to change the strings in an array of strings to uppercase.

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

static class Func
{
   static void Main(string[] args)
   {
      // Declare a Func variable and assign a lambda expression to the  
      // variable. The method takes a string and converts it to uppercase.
      Func<string, string> selector = str => str.ToUpper();
   
      // Create an array of strings.
      string[] words = { "orange", "apple", "Article", "elephant" };
      // Query the array and select strings according to the selector method.
      IEnumerable<String> aWords = words.Select(selector);
   
      // Output the results to the console.
      foreach (String word in aWords)
         Console.WriteLine(word);
   }
}      
/*
This code example produces the following output:
            
   ORANGE
   APPLE
   ARTICLE
   ELEPHANT
*/
Imports System.Collections.Generic
Imports System.Linq

Module Func
   Public Sub Main()
      ' Declare a Func variable and assign a lambda expression to the  
      ' variable. The method takes a string and converts it to uppercase.
      Dim selector As Func(Of String, String) = Function(str) str.ToUpper()
   
      ' Create an array of strings.
      Dim words() As String = { "orange", "apple", "Article", "elephant" }
      ' Query the array and select strings according to the selector method.
      Dim aWords As IEnumerable(Of String) = words.Select(selector)
   
      ' Output the results to the console.
      For Each word As String In aWords
         Console.WriteLine(word)
      Next
   End Sub
End Module
' This code example produces the following output:
'           
'   ORANGE
'   APPLE
'   ARTICLE
'   ELEPHANT

注解

可以使用此委托来表示可以作为参数传递而无需显式声明自定义委托的方法。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通过值传递给它的一个参数,并且它必须返回一个值。This means that the encapsulated method must have one parameter that is passed to it by value, and that it must return a value.

备注

若要引用的方法,有一个参数并返回void(或在 Visual Basic 中的声明为Sub而不是作为Function),使用泛型Action<T>改为委托。To reference a method that has one parameter and returns void (or in Visual Basic, that is declared as a Sub rather than as a Function), use the generic Action<T> delegate instead.

当你使用Func<T,TResult>委托时,您无需显式定义用于封装具有单个参数的方法的委托。When you use the Func<T,TResult> delegate, you do not have to explicitly define a delegate that encapsulates a method with a single parameter. 例如,下面的代码显式声明名为的委托ConvertMethod,并将分配到的引用UppercaseString给其委托实例的方法。For example, the following code explicitly declares a delegate named ConvertMethod and assigns a reference to the UppercaseString method to its delegate instance.

using System;

delegate string ConvertMethod(string inString);

public class DelegateExample
{
   public static void Main()
   {
      // Instantiate delegate to reference UppercaseString method
      ConvertMethod convertMeth = UppercaseString;
      string name = "Dakota";
      // Use delegate instance to call UppercaseString method
      Console.WriteLine(convertMeth(name));
   }

   private static string UppercaseString(string inputString)
   {
      return inputString.ToUpper();
   }
}
' Declare a delegate to represent string conversion method
Delegate Function ConvertMethod(ByVal inString As String) As String

Module DelegateExample
   Public Sub Main()
      ' Instantiate delegate to reference UppercaseString method
      Dim convertMeth As ConvertMethod = AddressOf UppercaseString
      Dim name As String = "Dakota"
      ' Use delegate instance to call UppercaseString method
      Console.WriteLine(convertMeth(name))
   End Sub

   Private Function UppercaseString(inputString As String) As String
      Return inputString.ToUpper()
   End Function
End Module

下面的示例简化了此代码实例化Func<T,TResult>而不是显式定义一个新委托,并为其赋值命名的方法的委托。The following example simplifies this code by instantiating the Func<T,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 UppercaseString method
      Func<string, string> convertMethod = UppercaseString;
      string name = "Dakota";
      // Use delegate instance to call UppercaseString method
      Console.WriteLine(convertMethod(name));
   }

   private static string UppercaseString(string inputString)
   {
      return inputString.ToUpper();
   }
}
Module GenericFunc
   Public Sub Main()
      ' Instantiate delegate to reference UppercaseString method
      Dim convertMethod As Func(Of String, String) = AddressOf UppercaseString
      Dim name As String = "Dakota"
      ' Use delegate instance to call UppercaseString method
      Console.WriteLine(convertMethod(name))
   End Sub

   Private Function UppercaseString(inputString As String) As String
      Return inputString.ToUpper()
   End Function
End Module

此外可以使用Func<T,TResult>委托与匿名方法在 C# 中,如以下示例所示。You can also use the Func<T,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, string> convert = delegate(string s)
         { return s.ToUpper();}; 
         
      string name = "Dakota";
      Console.WriteLine(convert(name));   
   }
}

你还可以分配一个 lambda 表达式到Func<T,TResult>委托,如以下示例所示。You can also assign a lambda expression to a Func<T,TResult> delegate, as the following example illustrates. (有关 lambda 表达式的简介,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()
   {
      Func<string, string> convert = s => s.ToUpper();
         
      string name = "Dakota";
      Console.WriteLine(convert(name));   
   }
}
Module LambdaExpression
   Public Sub Main()
      Dim convert As Func(Of String, String) = Function(s) s.ToUpper()
      
      Dim name As String = "Dakota"
      Console.WriteLine(convert(name))  
   End Sub
End Module

Lambda 表达式的基础类型是一个泛型Func委托。The underlying type of a lambda expression is one of the generic Func delegates. 这样,可以将 lambda 表达式作为参数传递而无需显式将其分配给委托。This makes it possible to pass a lambda expression as a parameter without explicitly assigning it to a delegate. 具体而言,因为许多方法中的类型System.Linq命名空间具有Func<T,TResult>参数,您可以将传递这些方法的 lambda 表达式无需显式实例化Func<T,TResult>委托。In particular, because many methods of types in the System.Linq namespace have Func<T,TResult> parameters, you can pass these methods a lambda expression without explicitly instantiating a Func<T,TResult> delegate.

扩展方法

GetMethodInfo(Delegate) GetMethodInfo(Delegate) GetMethodInfo(Delegate) 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.

适用于

另请参阅