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

定義

封裝具有一個參數並傳回 TResult 參數所指定之型別值的方法。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 

類型參數

T

這個委派所封裝之方法的參數型別。The type of the parameter of the method that this delegate encapsulates.

TResult

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

參數

arg

這個委派所封裝之方法的參數。The 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<T,TResult>Func<T,TResult>Func<T,TResult>Func<T,TResult>

範例

下列範例示範如何宣告及使用Func<T,TResult>委派。The following example demonstrates how to declare and use a Func<T,TResult> delegate. 這個範例會宣告Func<T,TResult>變數並將其指派的 lambda 運算式,將字串中的字元轉換成大寫。This example declares a Func<T,TResult> variable and assigns it a lambda expression that converts the characters in a string to uppercase. 委派會封裝這個方法會接著傳遞至Enumerable.Select方法,以變更為大寫的字串陣列中的字串。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

備註

您可以使用此委派来表示的方法,可以做為參數傳遞,而不必明確宣告自訂委派。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這個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由值傳遞給它的一個參數,而且它必須傳回值。This means that the encapsulated method must have one parameter that is passed to it by value, and that it must return a value.

注意

若要參考的方法具有一個參數並傳回void(或在 Visual Basic 中宣告為SubFunction),使用泛型Action<T>改為委派。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.

當您使用Func<T,TResult>委派,您不需要明確地定義這個委派會封裝具有單一參數的方法。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,下列程式碼明確宣告委派,名為ConvertMethod,並將指派的參考UppercaseString其委派執行個體的方法。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

下列範例中簡化這個程式碼,以具現化Func<T,TResult>而不是明確地定義新的委派,並為其指派具名的方法的委派。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

您也可以使用Func<T,TResult>具有在 C# 中,匿名方法委派,如下列範例所示。You can also use the Func<T,TResult> delegate with anonymous methods in C#, as the following example illustrates. (如匿名方法的簡介,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, string> convert = delegate(string s)
         { return s.ToUpper();}; 
         
      string name = "Dakota";
      Console.WriteLine(convert(name));   
   }
}

您也可以指派至 lambda 運算式Func<T,TResult>委派,如下列範例所示。You can also assign a lambda expression to a Func<T,TResult> delegate, as the following example illustrates. (如需 lambda 運算式,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()
   {
      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 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. 這讓您能夠傳遞做為參數的 lambda 運算式,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,因為有許多方法中的型別System.Linq命名空間一定Func<T,TResult>參數,您可以將這些方法的 lambda 運算式而不需要明確具現化Func<T,TResult>委派。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.

Extension Methods

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