Func<T1,T2,T3,TResult> 委托

定义

封装一个方法,该方法具有三个参数,且返回由 TResult 参数指定的类型的值。Encapsulates a method that has three parameters and returns a value of the type specified by the TResult parameter.

generic <typename T1, typename T2, typename T3, typename TResult>
public delegate TResult Func(T1 arg1, T2 arg2, T3 arg3);
public delegate TResult Func<in T1,in T2,in T3,out TResult>(T1 arg1, T2 arg2, T3 arg3);
public delegate TResult Func<T1,T2,T3,TResult>(T1 arg1, T2 arg2, T3 arg3);
type Func<'T1, 'T2, 'T3, 'Result> = delegate of 'T1 * 'T2 * 'T3 -> 'Result
Public Delegate Function Func(Of In T1, In T2, In T3, Out TResult)(arg1 As T1, arg2 As T2, arg3 As T3) As TResult 
Public Delegate Function Func(Of T1, T2, T3, TResult)(arg1 As T1, arg2 As T2, arg3 As T3) As TResult 

类型参数

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.

这是逆变类型参数。 即,可以使用指定的类型,也可以使用派生程度较低的任何类型。 有关协变和逆变的详细信息,请参阅泛型中的协变和逆变
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.

这是逆变类型参数。 即,可以使用指定的类型,也可以使用派生程度较低的任何类型。 有关协变和逆变的详细信息,请参阅泛型中的协变和逆变
T3

此委托封装的方法的第三个参数的类型。The type of the third parameter of the method that this delegate encapsulates.

这是逆变类型参数。 即,可以使用指定的类型,也可以使用派生程度较低的任何类型。 有关协变和逆变的详细信息,请参阅泛型中的协变和逆变
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.

这是协变类型参数。 即,可以使用指定的类型,也可以使用派生程度较高的任何类型。 有关协变和逆变的详细信息,请参阅泛型中的协变和逆变

参数

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.

arg3
T3

此委托封装的方法的第三个参数。The third 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<T1,T2,T3,TResult>

示例

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 值并将 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. true如果参数的长度等于参数的值,则 lambda 表达式将返回 String Int32The 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

注解

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三个参数,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 three parameters, each of which is passed to it by value, and that it must return a value.

备注

若要引用具有三个参数并返回 void (或在 Visual Basic 中(声明为 Sub 而不是) )的方法 Function ,请改用泛型 Action<T1,T2,T3> 委托。To reference a method that has three 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,T3> delegate instead.

使用 Func<T1,T2,T3,TResult> 委托时,无需显式定义使用三个参数封装方法的委托。When you use the Func<T1,T2,T3,TResult> delegate, you do not have to explicitly define a delegate that encapsulates a method with three parameters. 例如,下面的代码显式声明一个名为的泛型委托 ParseNumber ,并向 Parse 其委托实例分配对该方法的引用。For example, the following code explicitly declares a generic delegate named ParseNumber and assigns a reference to the Parse method to its delegate instance.

using System;
using System.Globalization;

delegate T ParseNumber<T>(string input, NumberStyles styles,
                         IFormatProvider provider);

public class DelegateExample
{
   public static void Main()
   {
      string numericString = "-1,234";
      ParseNumber<int> parser = int.Parse;
      Console.WriteLine(parser(numericString,
                        NumberStyles.Integer | NumberStyles.AllowThousands,
                        CultureInfo.InvariantCulture));
   }
}
Imports System.Globalization

Delegate Function ParseNumber(Of T)(input As String, styles As NumberStyles, _
                                    provider As IFormatProvider) As T

Module DelegateExample
   Public Sub Main()
      Dim numericString As String = "-1,234"
      Dim parser As ParseNumber(Of Integer) = AddressOf Integer.Parse
      Console.WriteLine(parser(numericString, _
                        NumberStyles.Integer Or NumberStyles.AllowThousands, _
                        CultureInfo.InvariantCulture))
   End Sub
End Module

下面的示例通过实例化委托来简化此代码 Func<T1,T2,T3,TResult> ,而不是显式定义一个新委托并为其分配一个命名方法。The following example simplifies this code by instantiating the Func<T1,T2,T3,TResult> delegate instead of explicitly defining a new delegate and assigning a named method to it.

using System;
using System.Globalization;

public class GenericFunc
{
   public static void Main()
   {
      string numericString = "-1,234";
      Func<string, NumberStyles, IFormatProvider, int> parser = int.Parse;
      Console.WriteLine(parser(numericString,
                        NumberStyles.Integer | NumberStyles.AllowThousands,
                        CultureInfo.InvariantCulture));
   }
}
Imports System.Globalization

Module GenericFunc
   Public Sub Main()
      Dim numericString As String = "-1,234"
      Dim parser As Func(Of String, NumberStyles, IFormatProvider, Integer) _
                         = AddressOf Integer.Parse
      Console.WriteLine(parser(numericString, _
                        NumberStyles.Integer Or NumberStyles.AllowThousands, _
                        CultureInfo.InvariantCulture))
   End Sub
End Module

可以 Func<T1,T2,T3,TResult> 在 c # 中将委托与匿名方法一起使用,如下例所示。You can use the Func<T1,T2,T3,TResult> delegate with anonymous methods in C#, as the following example illustrates. (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;
using System.Globalization;

public class Anonymous
{
   public static void Main()
   {
      string numericString = "-1,234";
      Func<string, NumberStyles, IFormatProvider, int> parser =
           delegate(string s, NumberStyles sty, IFormatProvider p)
           { return int.Parse(s, sty, p); };
      Console.WriteLine(parser(numericString,
                        NumberStyles.Integer | NumberStyles.AllowThousands,
                        CultureInfo.InvariantCulture));
   }
}

你还可以将 lambda 表达式分配给 Func<T1,T2,T3,TResult> 委托,如下面的示例所示。You can also assign a lambda expression to a Func<T1,T2,T3,TResult> delegate, as the following example illustrates. 有关 lambda 表达式介绍的 (,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;
using System.Globalization;

public class LambdaExpression
{
   public static void Main()
   {
      string numericString = "-1,234";
      Func<string, NumberStyles, IFormatProvider, int> parser = (s, sty, p)
                   => int.Parse(s, sty, p);
      Console.WriteLine(parser(numericString,
                        NumberStyles.Integer | NumberStyles.AllowThousands,
                        CultureInfo.InvariantCulture));
   }
}
Imports System.Globalization

Module LambdaExpression
   Public Sub Main()
      Dim numericString As String = "-1,234"
      Dim parser As Func(Of String, NumberStyles, IFormatProvider, Integer) _
                         = Function(s, sty, p) Integer.Parse(s, sty, p)
      Console.WriteLine(parser(numericString, _
                        NumberStyles.Integer Or NumberStyles.AllowThousands, _
                        CultureInfo.InvariantCulture))
   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,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. 具体而言,因为命名空间中的许多类型的方法 System.Linq 都有 Func 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 委托。In particular, because many methods of types in the System.Linq namespace have Func parameters, you can pass these methods a lambda expression without explicitly instantiating a Func delegate.

扩展方法

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