Func<T,TResult> 代理人

定義

封裝具有一個參數並傳回 TResult 參數指定類型之值的方法。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);
public delegate TResult Func<T,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 
Public Delegate Function Func(Of T, TResult)(arg As T) As TResult 

類型參數

T

這個委派所封裝之方法的參數類型。The type of the 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

arg
T

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>

範例

下列範例示範如何宣告和使用 Func<T,TResult> 委派。The following example demonstrates how to declare and use a Func<T,TResult> delegate. 此範例會宣告 Func<T,TResult> 變數,並為其指派 lambda 運算式,將字串中的字元轉換為大寫。This example declares a Func<T,TResult> variable and assigns it a lambda expression that converts the characters in a string to uppercase. 封裝這個方法的委派會接著傳遞至 Enumerable.Select 方法,以將字串陣列中的字串變更為大寫。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.

// 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

您可以使用這個委派來代表可以傳遞為參數的方法,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至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有一個以傳值方式傳遞給它的參數,而且必須傳回值。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

若要參考具有一個參數的方法,並傳回 void (或 Visual Basic 中宣告為, Sub 而不是做為) 的方法 Function ,請改用泛型 Action<T> 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> 委派時,不需要明確地定義委派,此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,下列程式碼會明確宣告名為的委派 ConvertMethod ,並將該方法的參考指派 UppercaseString 給它的委派實例。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

下列範例會藉由具現化委派來簡化此程式碼 Func<T,TResult> ,而不是明確定義新的委派,並將命名方法指派給它。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.

// 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));

string UppercaseString(string inputString)
{
   return inputString.ToUpper();
}

// This code example produces the following output:
//
//    DAKOTA
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 Func<T,TResult> 在 c # 中搭配匿名方法使用委派,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. 如需匿名方法的簡介,請參閱 匿名方法 (。 ) (For an introduction to anonymous methods, see Anonymous Methods.)

 Func<string, string> convert = delegate(string s)
    { return s.ToUpper();};

 string name = "Dakota";
 Console.WriteLine(convert(name));

// This code example produces the following output:
//
//    DAKOTA

您也可以將 lambda 運算式指派給 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.)

Func<string, string> convert = s => s.ToUpper();

string name = "Dakota";
Console.WriteLine(convert(name));

// This code example produces the following output:
//
//    DAKOTA
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. 如此一來,您就可以將 lambda 運算式當做參數傳遞,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. 尤其是,由於命名空間中的許多類型方法 System.Linq 都有 Func<T,TResult> 參數,您可以將這些方法傳遞給 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.

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