Func<T1,T2,TResult> 委托
定义
封装一个方法,该方法具有两个参数,并返回由 TResult 参数指定的类型的值。Encapsulates a method that has two parameters and returns a value of the type specified by the TResult parameter.
generic <typename T1, typename T2, typename TResult>
public delegate TResult Func(T1 arg1, T2 arg2);
public delegate TResult Func<in T1,in T2,out TResult>(T1 arg1, T2 arg2);
public delegate TResult Func<T1,T2,TResult>(T1 arg1, T2 arg2);
type Func<'T1, 'T2, 'Result> = delegate of 'T1 * 'T2 -> 'Result
Public Delegate Function Func(Of In T1, In T2, Out TResult)(arg1 As T1, arg2 As T2) As TResult
Public Delegate Function Func(Of T1, T2, TResult)(arg1 As T1, arg2 As T2) 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。- 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.
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.
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 Int32 。The 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两个参数,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 two parameters, each of which is passed to it by value, and that it must return a value.
备注
若要引用一个方法,该方法具有两个参数并返回 void (或在 Visual Basic 中(声明为 Sub 而不是 Function) ),请改用泛型 Action<T1,T2> 委托。To reference a method that has two 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> delegate instead.
使用 Func<T1,T2,TResult> 委托时,无需显式定义一个委托,该委托封装带有两个参数的方法。When you use the Func<T1,T2,TResult> delegate you do not have to explicitly define a delegate that encapsulates a method with two parameters. 例如,下面的代码显式声明一个名为的委托 ExtractMethod ,并向 ExtractWords 其委托实例分配对该方法的引用。For example, the following code explicitly declares a delegate named ExtractMethod and assigns a reference to the ExtractWords method to its delegate instance.
using System;
delegate string[] ExtractMethod(string stringToManipulate, int maximum);
public class DelegateExample
{
public static void Main()
{
// Instantiate delegate to reference ExtractWords method
ExtractMethod extractMeth = ExtractWords;
string title = "The Scarlet Letter";
// Use delegate instance to call ExtractWords method and display result
foreach (string word in extractMeth(title, 5))
Console.WriteLine(word);
}
private static string[] ExtractWords(string phrase, int limit)
{
char[] delimiters = new char[] {' '};
if (limit > 0)
return phrase.Split(delimiters, limit);
else
return phrase.Split(delimiters);
}
}
' Declare a delegate to represent string extraction method
Delegate Function ExtractMethod(ByVal stringToManipulate As String, _
ByVal maximum As Integer) As String()
Module DelegateExample
Public Sub Main()
' Instantiate delegate to reference ExtractWords method
Dim extractMeth As ExtractMethod = AddressOf ExtractWords
Dim title As String = "The Scarlet Letter"
' Use delegate instance to call ExtractWords method and display result
For Each word As String In extractMeth(title, 5)
Console.WriteLine(word)
Next
End Sub
Private Function ExtractWords(phrase As String, limit As Integer) As String()
Dim delimiters() As Char = {" "c}
If limit > 0 Then
Return phrase.Split(delimiters, limit)
Else
Return phrase.Split(delimiters)
End If
End Function
End Module
下面的示例通过实例化委托来简化此代码 Func<T1,T2,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 a Func<T1,T2,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 ExtractWords method
Func<string, int, string[]> extractMethod = ExtractWords;
string title = "The Scarlet Letter";
// Use delegate instance to call ExtractWords method and display result
foreach (string word in extractMethod(title, 5))
Console.WriteLine(word);
}
private static string[] ExtractWords(string phrase, int limit)
{
char[] delimiters = new char[] {' '};
if (limit > 0)
return phrase.Split(delimiters, limit);
else
return phrase.Split(delimiters);
}
}
Module GenericFunc
Public Sub Main()
' Instantiate delegate to reference ExtractWords method
Dim extractMeth As Func(Of String, Integer, String()) = AddressOf ExtractWords
Dim title As String = "The Scarlet Letter"
' Use delegate instance to call ExtractWords method and display result
For Each word As String In extractMeth(title, 5)
Console.WriteLine(word)
Next
End Sub
Private Function ExtractWords(phrase As String, limit As Integer) As String()
Dim delimiters() As Char = {" "c}
If limit > 0 Then
Return phrase.Split(delimiters, limit)
Else
Return phrase.Split(delimiters)
End If
End Function
End Module
可以 Func<T1,T2,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,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;
public class Anonymous
{
public static void Main()
{
Func<string, int, string[]> extractMeth = delegate(string s, int i)
{ char[] delimiters = new char[] {' '};
return i > 0 ? s.Split(delimiters, i) : s.Split(delimiters);
};
string title = "The Scarlet Letter";
// Use Func instance to call ExtractWords method and display result
foreach (string word in extractMeth(title, 5))
Console.WriteLine(word);
}
}
你还可以将 lambda 表达式分配给 Func<T1,T2,TResult> 委托,如下面的示例所示。You can also assign a lambda expression to a Func<T1,T2,TResult> delegate, as the following example illustrates. 有关 lambda 表达式介绍的 (,请参阅 Lambda 表达式 和 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()
{
char[] separators = new char[] {' '};
Func<string, int, string[]> extract = (s, i) =>
i > 0 ? s.Split(separators, i) : s.Split(separators) ;
string title = "The Scarlet Letter";
// Use Func instance to call ExtractWords method and display result
foreach (string word in extract(title, 5))
Console.WriteLine(word);
}
}
Module LambdaExpression
Public Sub Main()
Dim separators() As Char = {" "c}
Dim extract As Func(Of String, Integer, String()) = Function(s, i) _
CType(iif(i > 0, s.Split(separators, i), s.Split(separators)), String())
Dim title As String = "The Scarlet Letter"
For Each word As String In extract(title, 5)
Console.WriteLine(word)
Next
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<T1,T2,TResult> 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<T1,T2,TResult> 委托。In particular, because many methods of types in the System.Linq namespace have Func<T1,T2,TResult> parameters, you can pass these methods a lambda expression without explicitly instantiating a Func<T1,T2,TResult> 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. |