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);
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類型。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類型。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>

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. 這個範例會宣告 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. 封裝這個方法的委派隨後會傳遞至 Enumerable.Select 方法,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.

注意

本文中的某些 C# 範例會在 Try.NET 內嵌程式碼執行器和測試區執行。Some of the C# examples in this article run in the Try.NET inline code runner and playground. 請選取 [執行] 按鈕 (若該按鈕存在) 以在互動式視窗中執行範例。When present, select the Run button to run an example in an interactive window. 執行程式碼之後,您便可以修改它,並再選取一次 [執行] 來執行修改過的程式碼。Once you execute the code, you can modify it and run the modified code by selecting Run again. 修改過的程式碼會在互動式視窗中執行,或是如果編譯失敗的話,互動式視窗會顯示所有 C# 編譯器錯誤訊息。The modified code either runs in the interactive window or, if compilation fails, the interactive window displays all C# compiler error messages.

// 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表示可當做參數傳遞的方法,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到此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 (或在 Visual Basic 中,宣告為 Sub 而不是 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,您不需要明確地定義以單一參數封裝方法的委派。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 ConvertMethod 的委派,並將 UppercaseString 方法的參考指派給其委派實例。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 Func<T,TResult> 委派來簡化此程式碼,而不是明確定義新的委派,並將已命名的方法指派給它。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

您也可以在中C#使用 Func<T,TResult> 委派與匿名方法,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,您就可以傳遞 lambda 運算式做為參數,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 System.Linq 命名空間中類型的許多方法都具有 Func<T,TResult> 參數,您可以將這些方法傳遞至 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