Číst v angličtině Upravit

Sdílet prostřednictvím


Func<T1,T2,T3,T4,TResult> Delegate

Definition

Encapsulates a method that has four parameters and returns a value of the type specified by the TResult parameter.

public delegate TResult Func<in T1,in T2,in T3,in T4,out TResult>(T1 arg1, T2 arg2, T3 arg3, T4 arg4);
public delegate TResult Func<T1,T2,T3,T4,TResult>(T1 arg1, T2 arg2, T3 arg3, T4 arg4);

Type Parameters

T1

The type of the first parameter of the method that this delegate encapsulates.

This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.
T2

The type of the second parameter of the method that this delegate encapsulates.

This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.
T3

The type of the third parameter of the method that this delegate encapsulates.

This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.
T4

The type of the fourth parameter of the method that this delegate encapsulates.

This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.
TResult

The type of the return value of the method that this delegate encapsulates.

This type parameter is covariant. That is, you can use either the type you specified or any type that is more derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.

Parameters

arg1
T1

The first parameter of the method that this delegate encapsulates.

arg2
T2

The second parameter of the method that this delegate encapsulates.

arg3
T3

The third parameter of the method that this delegate encapsulates.

arg4
T4

The fourth parameter of the method that this delegate encapsulates.

Return Value

TResult

The return value of the method that this delegate encapsulates.

Examples

The following example demonstrates how to declare and use a Func<T1,T2,TResult> delegate. 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. The lambda expression returns true if the length of the String parameter is equal to the value of the Int32 parameter. 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);
   }
}

Remarks

You can use this delegate to represent a method that can be passed as a parameter without explicitly declaring a custom delegate. The encapsulated method must correspond to the method signature that is defined by this delegate. This means that the encapsulated method must have four parameters, each of which is passed to it by value, and that it must return a value.

Poznámka

To reference a method that has four parameters and returns void (unit in F#) (or in Visual Basic, that is declared as a Sub rather than as a Function), use the generic Action<T1,T2,T3,T4> delegate instead.

When you use the Func<T1,T2,T3,T4,TResult> delegate, you do not have to explicitly define a delegate that encapsulates a method with four parameters. For example, the following code explicitly declares a generic delegate named Searcher and assigns a reference to the IndexOf method to its delegate instance.

using System;

delegate int Searcher(string searchString, int start, int count,
                         StringComparison type);

public class DelegateExample
{
   public static void Main()
   {
      string title = "The House of the Seven Gables";
      int position = 0;
      Searcher finder = title.IndexOf;
      do
      {
         int characters = title.Length - position;
         position = finder("the", position, characters,
                         StringComparison.InvariantCultureIgnoreCase);
         if (position >= 0)
         {
            position++;
            Console.WriteLine("'The' found at position {0} in {1}.",
                              position, title);
         }
      } while (position > 0);
   }
}

The following example simplifies this code by instantiating the Func<T1,T2,T3,T4,TResult> delegate instead of explicitly defining a new delegate and assigning a named method to it.

using System;

public class DelegateExample
{
   public static void Main()
   {
      string title = "The House of the Seven Gables";
      int position = 0;
      Func<string, int, int, StringComparison, int> finder = title.IndexOf;
      do
      {
         int characters = title.Length - position;
         position = finder("the", position, characters,
                         StringComparison.InvariantCultureIgnoreCase);
         if (position >= 0)
         {
            position++;
            Console.WriteLine("'The' found at position {0} in {1}.",
                              position, title);
         }
      } while (position > 0);
   }
}

You can use the Func<T1,T2,T3,T4,TResult> delegate with anonymous methods in C#, as the following example illustrates. (For an introduction to anonymous methods, see Anonymous Methods.)

using System;

public class DelegateExample
{
   public static void Main()
   {
      string title = "The House of the Seven Gables";
      int position = 0;
      Func<string, int, int, StringComparison, int> finder =
           delegate(string s, int pos, int chars, StringComparison type)
           { return title.IndexOf(s, pos, chars, type); };
      do
      {
         int characters = title.Length - position;
         position = finder("the", position, characters,
                         StringComparison.InvariantCultureIgnoreCase);
         if (position >= 0)
         {
            position++;
            Console.WriteLine("'The' found at position {0} in {1}.",
                              position, title);
         }
      } while (position > 0);
   }
}

You can also assign a lambda expression to a Func<T1,T2,TResult> delegate, as the following example illustrates. (For an introduction to lambda expressions, see Lambda Expressions (VB), Lambda Expressions (C#) and Lambda Expressions (F#).)

using System;

public class DelegateExample
{
   public static void Main()
   {
      string title = "The House of the Seven Gables";
      int position = 0;
      Func<string, int, int, StringComparison, int> finder =
           (s, pos, chars, type) => title.IndexOf(s, pos, chars, type);
      do
      {
         int characters = title.Length - position;
         position = finder("the", position, characters,
                         StringComparison.InvariantCultureIgnoreCase);
         if (position >= 0)
         {
            position++;
            Console.WriteLine("'The' found at position {0} in {1}.",
                              position, title);
         }
      } while (position > 0);
   }
}

The underlying type of a lambda expression is one of the generic Func delegates. This makes it possible to pass a lambda expression as a parameter without explicitly assigning it to a delegate. 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.

Extension Methods

GetMethodInfo(Delegate)

Gets an object that represents the method represented by the specified delegate.

Applies to

See also