Métodos System.Delegate.CreateDelegate
En este artículo se proporcionan comentarios adicionales a la documentación de referencia de esta API.
Los CreateDelegate métodos crean un delegado de un tipo especificado.
Método CreateDelegate(Type, MethodInfo)
Esta sobrecarga de método es equivalente a llamar a la sobrecarga del CreateDelegate(Type, MethodInfo, Boolean) método y especificar true
para throwOnBindFailure
.
Ejemplos
Esta sección contiene dos ejemplos de código. En el primer ejemplo se muestran los dos tipos de delegados que se pueden crear con esta sobrecarga de método: abrir sobre un método de instancia y abrir a través de un método estático.
En el segundo ejemplo de código se muestran los tipos de parámetros compatibles y los tipos de valor devuelto.
Ejemplo 1
En el ejemplo de código siguiente se muestran las dos formas en que se puede crear un delegado mediante esta sobrecarga del CreateDelegate método .
Nota:
Hay dos sobrecargas del CreateDelegate método que especifican un MethodInfo pero no un primer argumento; su funcionalidad es la misma, excepto que una le permite especificar si se produce un error al enlazar y la otra siempre produce. En este ejemplo de código se usan ambas sobrecargas.
En el ejemplo se declara una clase C
con un método estático y un método M1
M2
de instancia , y dos tipos de delegado: D1
toma una instancia de C
y una cadena y D2
toma una cadena.
Una segunda clase denominada Example
contiene el código que crea los delegados.
- Se crea un delegado de tipo
D1
, que representa un método de instancia abierta, para el métodoM1
de instancia . Se debe pasar una instancia cuando se invoca el delegado. - Se crea un delegado de tipo
D2
, que representa un método estático abierto, para el métodoM2
estático .
using System;
using System.Reflection;
// Declare three delegate types for demonstrating the combinations
// of static versus instance methods and open versus closed
// delegates.
//
public delegate void D1(C c, string s);
public delegate void D2(string s);
public delegate void D3();
// A sample class with an instance method and a static method.
//
public class C
{
private int id;
public C(int id) { this.id = id; }
public void M1(string s)
{
Console.WriteLine("Instance method M1 on C: id = {0}, s = {1}",
this.id, s);
}
public static void M2(string s)
{
Console.WriteLine("Static method M2 on C: s = {0}", s);
}
}
public class Example2
{
public static void Main()
{
C c1 = new C(42);
// Get a MethodInfo for each method.
//
MethodInfo mi1 = typeof(C).GetMethod("M1",
BindingFlags.Public | BindingFlags.Instance);
MethodInfo mi2 = typeof(C).GetMethod("M2",
BindingFlags.Public | BindingFlags.Static);
D1 d1;
D2 d2;
D3 d3;
Console.WriteLine("\nAn instance method closed over C.");
// In this case, the delegate and the
// method must have the same list of argument types; use
// delegate type D2 with instance method M1.
//
Delegate test =
Delegate.CreateDelegate(typeof(D2), c1, mi1, false);
// Because false was specified for throwOnBindFailure
// in the call to CreateDelegate, the variable 'test'
// contains null if the method fails to bind (for
// example, if mi1 happened to represent a method of
// some class other than C).
//
if (test != null)
{
d2 = (D2)test;
// The same instance of C is used every time the
// delegate is invoked.
d2("Hello, World!");
d2("Hi, Mom!");
}
Console.WriteLine("\nAn open instance method.");
// In this case, the delegate has one more
// argument than the instance method; this argument comes
// at the beginning, and represents the hidden instance
// argument of the instance method. Use delegate type D1
// with instance method M1.
//
d1 = (D1)Delegate.CreateDelegate(typeof(D1), null, mi1);
// An instance of C must be passed in each time the
// delegate is invoked.
//
d1(c1, "Hello, World!");
d1(new C(5280), "Hi, Mom!");
Console.WriteLine("\nAn open static method.");
// In this case, the delegate and the method must
// have the same list of argument types; use delegate type
// D2 with static method M2.
//
d2 = (D2)Delegate.CreateDelegate(typeof(D2), null, mi2);
// No instances of C are involved, because this is a static
// method.
//
d2("Hello, World!");
d2("Hi, Mom!");
Console.WriteLine("\nA static method closed over the first argument (String).");
// The delegate must omit the first argument of the method.
// A string is passed as the firstArgument parameter, and
// the delegate is bound to this string. Use delegate type
// D3 with static method M2.
//
d3 = (D3)Delegate.CreateDelegate(typeof(D3),
"Hello, World!", mi2);
// Each time the delegate is invoked, the same string is
// used.
d3();
}
}
/* This code example produces the following output:
An instance method closed over C.
Instance method M1 on C: id = 42, s = Hello, World!
Instance method M1 on C: id = 42, s = Hi, Mom!
An open instance method.
Instance method M1 on C: id = 42, s = Hello, World!
Instance method M1 on C: id = 5280, s = Hi, Mom!
An open static method.
Static method M2 on C: s = Hello, World!
Static method M2 on C: s = Hi, Mom!
A static method closed over the first argument (String).
Static method M2 on C: s = Hello, World!
*/
open System
open System.Reflection
// A sample class with an instance method and a static method.
type C(id) =
member _.M1(s) =
printfn $"Instance method M1 on C: id = %i{id}, s = %s{s}"
static member M2(s) =
printfn $"Static method M2 on C: s = %s{s}"
// Declare three delegate types for demonstrating the combinations
// of static versus instance methods and open versus closed
// delegates.
type D1 = delegate of C * string -> unit
type D2 = delegate of string -> unit
type D3 = delegate of unit -> unit
let c1 = C 42
// Get a MethodInfo for each method.
//
let mi1 = typeof<C>.GetMethod("M1", BindingFlags.Public ||| BindingFlags.Instance)
let mi2 = typeof<C>.GetMethod("M2", BindingFlags.Public ||| BindingFlags.Static)
printfn "\nAn instance method closed over C."
// In this case, the delegate and the
// method must have the same list of argument types use
// delegate type D2 with instance method M1.
let test = Delegate.CreateDelegate(typeof<D2>, c1, mi1, false)
// Because false was specified for throwOnBindFailure
// in the call to CreateDelegate, the variable 'test'
// contains null if the method fails to bind (for
// example, if mi1 happened to represent a method of
// some class other than C).
if test <> null then
let d2 = test :?> D2
// The same instance of C is used every time the
// delegate is invoked.
d2.Invoke "Hello, World!"
d2.Invoke "Hi, Mom!"
printfn "\nAn open instance method."
// In this case, the delegate has one more
// argument than the instance method this argument comes
// at the beginning, and represents the hidden instance
// argument of the instance method. Use delegate type D1
// with instance method M1.
let d1 = Delegate.CreateDelegate(typeof<D1>, null, mi1) :?> D1
// An instance of C must be passed in each time the
// delegate is invoked.
d1.Invoke(c1, "Hello, World!")
d1.Invoke(C 5280, "Hi, Mom!")
printfn "\nAn open static method."
// In this case, the delegate and the method must
// have the same list of argument types use delegate type
// D2 with static method M2.
let d2 = Delegate.CreateDelegate(typeof<D2>, null, mi2) :?> D2
// No instances of C are involved, because this is a static
// method.
d2.Invoke "Hello, World!"
d2.Invoke "Hi, Mom!"
printfn "\nA static method closed over the first argument (String)."
// The delegate must omit the first argument of the method.
// A string is passed as the firstArgument parameter, and
// the delegate is bound to this string. Use delegate type
// D3 with static method M2.
let d3 = Delegate.CreateDelegate(typeof<D3>, "Hello, World!", mi2) :?> D3
// Each time the delegate is invoked, the same string is used.
d3.Invoke()
// This code example produces the following output:
// An instance method closed over C.
// Instance method M1 on C: id = 42, s = Hello, World!
// Instance method M1 on C: id = 42, s = Hi, Mom!
//
// An open instance method.
// Instance method M1 on C: id = 42, s = Hello, World!
// Instance method M1 on C: id = 5280, s = Hi, Mom!
//
// An open static method.
// Static method M2 on C: s = Hello, World!
// Static method M2 on C: s = Hi, Mom!
//
// A static method closed over the first argument (String).
// Static method M2 on C: s = Hello, World!
Imports System.Reflection
Imports System.Security.Permissions
' Declare three delegate types for demonstrating the combinations
' of Shared versus instance methods and open versus closed
' delegates.
'
Public Delegate Sub D1(ByVal c As C2, ByVal s As String)
Public Delegate Sub D2(ByVal s As String)
Public Delegate Sub D3()
' A sample class with an instance method and a Shared method.
'
Public Class C2
Private id As Integer
Public Sub New(ByVal id As Integer)
Me.id = id
End Sub
Public Sub M1(ByVal s As String)
Console.WriteLine("Instance method M1 on C2: id = {0}, s = {1}",
Me.id, s)
End Sub
Public Shared Sub M2(ByVal s As String)
Console.WriteLine("Shared method M2 on C2: s = {0}", s)
End Sub
End Class
Public Class Example2
Public Shared Sub Main()
Dim c1 As New C2(42)
' Get a MethodInfo for each method.
'
Dim mi1 As MethodInfo = GetType(C2).GetMethod("M1",
BindingFlags.Public Or BindingFlags.Instance)
Dim mi2 As MethodInfo = GetType(C2).GetMethod("M2",
BindingFlags.Public Or BindingFlags.Static)
Dim d1 As D1
Dim d2 As D2
Dim d3 As D3
Console.WriteLine(vbLf & "An instance method closed over C2.")
' In this case, the delegate and the
' method must have the same list of argument types; use
' delegate type D2 with instance method M1.
'
Dim test As [Delegate] =
[Delegate].CreateDelegate(GetType(D2), c1, mi1, False)
' Because False was specified for throwOnBindFailure
' in the call to CreateDelegate, the variable 'test'
' contains Nothing if the method fails to bind (for
' example, if mi1 happened to represent a method of
' some class other than C2).
'
If test IsNot Nothing Then
d2 = CType(test, D2)
' The same instance of C2 is used every time the
' delegate is invoked.
d2("Hello, World!")
d2("Hi, Mom!")
End If
Console.WriteLine(vbLf & "An open instance method.")
' In this case, the delegate has one more
' argument than the instance method; this argument comes
' at the beginning, and represents the hidden instance
' argument of the instance method. Use delegate type D1
' with instance method M1.
'
d1 = CType([Delegate].CreateDelegate(GetType(D1), Nothing, mi1), D1)
' An instance of C2 must be passed in each time the
' delegate is invoked.
'
d1(c1, "Hello, World!")
d1(New C2(5280), "Hi, Mom!")
Console.WriteLine(vbLf & "An open Shared method.")
' In this case, the delegate and the method must
' have the same list of argument types; use delegate type
' D2 with Shared method M2.
'
d2 = CType([Delegate].CreateDelegate(GetType(D2), Nothing, mi2), D2)
' No instances of C2 are involved, because this is a Shared
' method.
'
d2("Hello, World!")
d2("Hi, Mom!")
Console.WriteLine(vbLf & "A Shared method closed over the first argument (String).")
' The delegate must omit the first argument of the method.
' A string is passed as the firstArgument parameter, and
' the delegate is bound to this string. Use delegate type
' D3 with Shared method M2.
'
d3 = CType([Delegate].CreateDelegate(GetType(D3), "Hello, World!", mi2), D3)
' Each time the delegate is invoked, the same string is
' used.
d3()
End Sub
End Class
' This code example produces the following output:
'
'An instance method closed over C2.
'Instance method M1 on C2: id = 42, s = Hello, World!
'Instance method M1 on C2: id = 42, s = Hi, Mom!
'
'An open instance method.
'Instance method M1 on C2: id = 42, s = Hello, World!
'Instance method M1 on C2: id = 5280, s = Hi, Mom!
'
'An open Shared method.
'Shared method M2 on C2: s = Hello, World!
'Shared method M2 on C2: s = Hi, Mom!
'
'A Shared method closed over the first argument (String).
'Shared method M2 on C2: s = Hello, World!
'
Ejemplo 2
En el ejemplo de código siguiente se muestra la compatibilidad de tipos de parámetros y tipos devueltos.
En el ejemplo de código se define una clase base denominada Base
y una clase denominada Derived
que deriva de Base
. La clase derivada tiene un static
método (Shared
en Visual Basic) denominado MyMethod
con un parámetro de tipo Base
y un tipo de valor devuelto de Derived
. El ejemplo de código también define un delegado denominado Example
que tiene un parámetro de tipo Derived
y un tipo de valor devuelto de Base
.
En el ejemplo de código se muestra que el delegado denominado Example
se puede usar para representar el método MyMethod
. El método se puede enlazar al delegado porque:
- El tipo de parámetro del delegado (
Derived
) es más restrictivo que el tipo de parámetro (MyMethod
Base
), por lo que siempre es seguro pasar el argumento del delegado aMyMethod
. - El tipo de valor devuelto de
MyMethod
(Derived
) es más restrictivo que el tipo de parámetro del delegado (Base
), por lo que siempre es seguro convertir el tipo de valor devuelto del método al tipo de valor devuelto del delegado.
El ejemplo de código no genera ninguna salida.
using System;
using System.Reflection;
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
//
public class Base { }
public class Derived : Base
{
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
//
public static Derived MyMethod(Base arg)
{
Base dummy = arg;
return new Derived();
}
}
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
//
public delegate Base Example5(Derived arg);
class Test
{
public static void Main()
{
// The binding flags needed to retrieve MyMethod.
BindingFlags flags = BindingFlags.Public | BindingFlags.Static;
// Get a MethodInfo that represents MyMethod.
MethodInfo minfo = typeof(Derived).GetMethod("MyMethod", flags);
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example5 to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example5 (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
//
Example5 ex =
(Example5)Delegate.CreateDelegate(typeof(Example5), minfo);
// Execute MyMethod using the delegate Example5.
//
Base b = ex(new Derived());
}
}
open System
open System.Reflection
// Define two classes to use in the demonstration, a base class and
// a class that derives from it.
type Base() = class end
type Derived() =
inherit Base()
// Define a static method to use in the demonstration. The method
// takes an instance of Base and returns an instance of Derived.
// For the purposes of the demonstration, it is not necessary for
// the method to do anything useful.
static member MyMethod(arg: Base) =
Derived()
// Define a delegate that takes an instance of Derived and returns an
// instance of Base.
type Example = delegate of Derived -> Base
// The binding flags needed to retrieve MyMethod.
let flags = BindingFlags.Public ||| BindingFlags.Static
// Get a MethodInfo that represents MyMethod.
let minfo = typeof<Derived>.GetMethod("MyMethod", flags)
// Demonstrate contravariance of parameter types and covariance
// of return types by using the delegate Example to represent
// MyMethod. The delegate binds to the method because the
// parameter of the delegate is more restrictive than the
// parameter of the method (that is, the delegate accepts an
// instance of Derived, which can always be safely passed to
// a parameter of type Base), and the return type of MyMethod
// is more restrictive than the return type of Example (that
// is, the method returns an instance of Derived, which can
// always be safely cast to type Base).
let ex = Delegate.CreateDelegate(typeof<Example>, minfo) :?> Example
// Execute MyMethod using the delegate Example.
let b = Derived() |> ex.Invoke
Imports System.Reflection
' Define two classes to use in the demonstration, a base class and
' a class that derives from it.
'
Public Class Base
End Class
Public Class Derived
Inherits Base
' Define a Shared method to use in the demonstration. The method
' takes an instance of Base and returns an instance of Derived.
' For the purposes of the demonstration, it is not necessary for
' the method to do anything useful.
'
Public Shared Function MyMethod(ByVal arg As Base) As Derived
Dim dummy As Base = arg
Return New Derived()
End Function
End Class
' Define a delegate that takes an instance of Derived and returns an
' instance of Base.
'
Public Delegate Function Example(ByVal arg As Derived) As Base
Module Test
Sub Main()
' The binding flags needed to retrieve MyMethod.
Dim flags As BindingFlags = _
BindingFlags.Public Or BindingFlags.Static
' Get a MethodInfo that represents MyMethod.
Dim minfo As MethodInfo = _
GetType(Derived).GetMethod("MyMethod", flags)
' Demonstrate contravariance of parameter types and covariance
' of return types by using the delegate Example to represent
' MyMethod. The delegate binds to the method because the
' parameter of the delegate is more restrictive than the
' parameter of the method (that is, the delegate accepts an
' instance of Derived, which can always be safely passed to
' a parameter of type Base), and the return type of MyMethod
' is more restrictive than the return type of Example (that
' is, the method returns an instance of Derived, which can
' always be safely cast to type Base).
'
Dim ex As Example = CType( _
[Delegate].CreateDelegate(GetType(Example), minfo), _
Example _
)
' Execute MyMethod using the delegate Example.
'
Dim b As Base = ex(New Derived())
End Sub
End Module
Métodos CreateDelegate(Type, Object, MethodInfo) y CreateDelegate(Type, Object, MethodInfo, Boolean)
La funcionalidad de estas dos sobrecargas es la misma, excepto que una permite especificar si se produce un error al enlazar y la otra siempre se produce.
El tipo delegado y el método deben tener tipos de valor devuelto compatibles. Es decir, el tipo de valor devuelto de method
debe ser asignable al tipo de valor devuelto de type
.
firstArgument
, el segundo parámetro para estas sobrecargas, es el primer argumento del método que representa el delegado. Si firstArgument
se proporciona, se pasa a method
cada vez que se invoca el delegado; firstArgument
se dice que está enlazado al delegado y se dice que el delegado se cierra sobre su primer argumento. Si method
es static
(Shared
en Visual Basic), la lista de argumentos proporcionada al invocar el delegado incluye todos los parámetros excepto el primero; si method
es un método de instancia, se firstArgument
pasa al parámetro de instancia oculta (representado por this
en C#, o por Me
en Visual Basic).
Si firstArgument
se proporciona, el primer parámetro de debe ser un tipo de method
referencia y firstArgument
debe ser compatible con ese tipo.
Importante
Si method
es static
(Shared
en Visual Basic) y su primer parámetro es de tipo Object o ValueType, puede firstArgument
ser un tipo de valor. En este caso firstArgument
, se conversión boxeada automáticamente. La conversión boxing automática no se produce para ningún otro argumento, como lo haría en una llamada de función de C# o Visual Basic.
Si firstArgument
es una referencia nula y method
es un método de instancia, el resultado depende de las firmas del tipo type
delegado y de method
:
- Si la firma de
type
incluye explícitamente el primer parámetro oculto demethod
, se dice que el delegado representa un método de instancia abierta. Cuando se invoca al delegado, el primer argumento de la lista de argumentos se pasa al parámetro de instancia oculta demethod
. - Si las firmas de y
type
coinciden (es decir, todos los tipos demethod
parámetros son compatibles), se dice que el delegado se cierra sobre una referencia nula. Invocar al delegado es como llamar a un método de instancia en una instancia nula, lo que no es algo especialmente útil para hacer.
Si firstArgument
es una referencia nula y method
es estática, el resultado depende de las firmas del tipo type
delegado y de method
:
- Si la firma de
method
ytype
coincide (es decir, todos los tipos de parámetros son compatibles), se dice que el delegado representa un método estático abierto. Este es el caso más común para los métodos estáticos. En este caso, puede obtener un rendimiento ligeramente mejor mediante la sobrecarga del CreateDelegate(Type, MethodInfo) método . - Si la firma de
type
comienza con el segundo parámetro demethod
y el resto de los tipos de parámetro son compatibles, se dice que el delegado se cierra sobre una referencia nula. Cuando se invoca al delegado, se pasa una referencia nula al primer parámetro demethod
.
Ejemplo
En el ejemplo de código siguiente se muestran todos los métodos que puede representar un único tipo de delegado: cerrado sobre un método de instancia, abierto a través de un método de instancia, abierto sobre un método estático y cerrado sobre un método estático.
En el ejemplo de código se definen dos clases, C
y F
, y un tipo D
de delegado con un argumento de tipo C
. Las clases tienen métodos estáticos M1
e de instancia coincidentes, M3
, y M4
, y clase C
también tiene un método M2
de instancia que no tiene argumentos.
Una tercera clase denominada Example
contiene el código que crea los delegados.
- Los delegados se crean para el método
M1
de instancia de tipoC
y tipoF
; cada uno se cierra sobre una instancia del tipo correspondiente. El métodoM1
de tipoC
muestra lasID
propiedades de la instancia enlazada y del argumento . - Se crea un delegado para el método
M2
de tipoC
. Se trata de un delegado de instancia abierta, en el que el argumento del delegado representa el primer argumento oculto en el método de instancia. El método no tiene ningún otro argumento. Se llama como si fuera un método estático. - Los delegados se crean para el método
M3
estático de tipoC
y tipoF
; son delegados estáticos abiertos. - Por último, los delegados se crean para el método
M4
estático de tipoC
y tipoF
; cada método tiene el tipo declarativo como primer argumento y se proporciona una instancia del tipo, por lo que los delegados se cierran sobre sus primeros argumentos. El métodoM4
de tipoC
muestra lasID
propiedades de la instancia enlazada y del argumento .
using System;
using System.Reflection;
// Declare a delegate type. The object of this code example
// is to show all the methods this delegate can bind to.
//
public delegate void D(C1 c);
// Declare two sample classes, C1 and F. Class C1 has an ID
// property so instances can be identified.
//
public class C1
{
private int id;
public int ID { get { return id; } }
public C1(int id) { this.id = id; }
public void M1(C1 c)
{
Console.WriteLine("Instance method M1(C1 c) on C1: this.id = {0}, c.ID = {1}",
this.id, c.ID);
}
public void M2()
{
Console.WriteLine("Instance method M2() on C1: this.id = {0}",
this.id);
}
public static void M3(C1 c)
{
Console.WriteLine("Static method M3(C1 c) on C1: c.ID = {0}", c.ID);
}
public static void M4(C1 c1, C1 c2)
{
Console.WriteLine("Static method M4(C1 c1, C1 c2) on C1: c1.ID = {0}, c2.ID = {1}",
c1.ID, c2.ID);
}
}
public class F
{
public void M1(C1 c)
{
Console.WriteLine("Instance method M1(C1 c) on F: c.ID = {0}",
c.ID);
}
public static void M3(C1 c)
{
Console.WriteLine("Static method M3(C1 c) on F: c.ID = {0}", c.ID);
}
public static void M4(F f, C1 c)
{
Console.WriteLine("Static method M4(F f, C1 c) on F: c.ID = {0}",
c.ID);
}
}
public class Example
{
public static void Main()
{
C1 c1 = new C1(42);
C1 c2 = new C1(1491);
F f1 = new F();
D d;
// Instance method with one argument of type C1.
MethodInfo cmi1 = typeof(C1).GetMethod("M1");
// Instance method with no arguments.
MethodInfo cmi2 = typeof(C1).GetMethod("M2");
// Static method with one argument of type C1.
MethodInfo cmi3 = typeof(C1).GetMethod("M3");
// Static method with two arguments of type C1.
MethodInfo cmi4 = typeof(C1).GetMethod("M4");
// Instance method with one argument of type C1.
MethodInfo fmi1 = typeof(F).GetMethod("M1");
// Static method with one argument of type C1.
MethodInfo fmi3 = typeof(F).GetMethod("M3");
// Static method with an argument of type F and an argument
// of type C1.
MethodInfo fmi4 = typeof(F).GetMethod("M4");
Console.WriteLine("\nAn instance method on any type, with an argument of type C1.");
// D can represent any instance method that exactly matches its
// signature. Methods on C1 and F are shown here.
//
d = (D)Delegate.CreateDelegate(typeof(D), c1, cmi1);
d(c2);
d = (D)Delegate.CreateDelegate(typeof(D), f1, fmi1);
d(c2);
Console.WriteLine("\nAn instance method on C1 with no arguments.");
// D can represent an instance method on C1 that has no arguments;
// in this case, the argument of D represents the hidden first
// argument of any instance method. The delegate acts like a
// static method, and an instance of C1 must be passed each time
// it is invoked.
//
d = (D)Delegate.CreateDelegate(typeof(D), null, cmi2);
d(c1);
Console.WriteLine("\nA static method on any type, with an argument of type C1.");
// D can represent any static method with the same signature.
// Methods on F and C1 are shown here.
//
d = (D)Delegate.CreateDelegate(typeof(D), null, cmi3);
d(c1);
d = (D)Delegate.CreateDelegate(typeof(D), null, fmi3);
d(c1);
Console.WriteLine("\nA static method on any type, with an argument of");
Console.WriteLine(" that type and an argument of type C1.");
// D can represent any static method with one argument of the
// type the method belongs and a second argument of type C1.
// In this case, the method is closed over the instance of
// supplied for the its first argument, and acts like an instance
// method. Methods on F and C1 are shown here.
//
d = (D)Delegate.CreateDelegate(typeof(D), c1, cmi4);
d(c2);
Delegate test =
Delegate.CreateDelegate(typeof(D), f1, fmi4, false);
// This final example specifies false for throwOnBindFailure
// in the call to CreateDelegate, so the variable 'test'
// contains Nothing if the method fails to bind (for
// example, if fmi4 happened to represent a method of
// some class other than F).
//
if (test != null)
{
d = (D)test;
d(c2);
}
}
}
/* This code example produces the following output:
An instance method on any type, with an argument of type C1.
Instance method M1(C1 c) on C1: this.id = 42, c.ID = 1491
Instance method M1(C1 c) on F: c.ID = 1491
An instance method on C1 with no arguments.
Instance method M2() on C1: this.id = 42
A static method on any type, with an argument of type C1.
Static method M3(C1 c) on C1: c.ID = 42
Static method M3(C1 c) on F: c.ID = 42
A static method on any type, with an argument of
that type and an argument of type C1.
Static method M4(C1 c1, C1 c2) on C1: c1.ID = 42, c2.ID = 1491
Static method M4(F f, C1 c) on F: c.ID = 1491
*/
open System
// Declare two sample classes, C and F. Class C has an ID
// property so instances can be identified.
type C(id) =
member _.ID = id
member _.M1(c: C) =
printfn $"Instance method M1(C c) on C: this.id = {id}, c.ID = {c.ID}"
member _.M2() =
printfn $"Instance method M2() on C: this.id = {id}"
static member M3(c: C) =
printfn $"Static method M3(C c) on C: c.ID = {c.ID}"
static member M4(c1: C, c2: C) =
printfn $"Static method M4(C c1, C c2) on C: c1.ID = {c1.ID}, c2.ID = {c2.ID}"
// Declare a delegate type. The object of this code example
// is to show all the methods this delegate can bind to.
type D = delegate of C -> unit
type F() =
member _.M1(c: C) =
printfn $"Instance method M1(C c) on F: c.ID = {c.ID}"
member _.M3(c: C) =
printfn $"Static method M3(C c) on F: c.ID = {c.ID}"
member _.M4(f: F, c: C) =
printfn $"Static method M4(F f, C c) on F: c.ID = {c.ID}"
[<EntryPoint>]
let main _ =
let c1 = C 42
let c2 = C 1491
let f1 = F()
// Instance method with one argument of type C.
let cmi1 = typeof<C>.GetMethod "M1"
// Instance method with no arguments.
let cmi2 = typeof<C>.GetMethod "M2"
// Static method with one argument of type C.
let cmi3 = typeof<C>.GetMethod "M3"
// Static method with two arguments of type C.
let cmi4 = typeof<C>.GetMethod "M4"
// Instance method with one argument of type C.
let fmi1 = typeof<F>.GetMethod "M1"
// Static method with one argument of type C.
let fmi3 = typeof<F>.GetMethod "M3"
// Static method with an argument of type F and an argument
// of type C.
let fmi4 = typeof<F>.GetMethod "M4"
printfn "\nAn instance method on any type, with an argument of type C."
// D can represent any instance method that exactly matches its
// signature. Methods on C and F are shown here.
let d = Delegate.CreateDelegate(typeof<D>, c1, cmi1) :?> D
d.Invoke c2
let d = Delegate.CreateDelegate(typeof<D>, f1, fmi1) :?> D
d.Invoke c2
Console.WriteLine("\nAn instance method on C with no arguments.")
// D can represent an instance method on C that has no arguments
// in this case, the argument of D represents the hidden first
// argument of any instance method. The delegate acts like a
// static method, and an instance of C must be passed each time
// it is invoked.
let d = Delegate.CreateDelegate(typeof<D>, null, cmi2) :?> D
d.Invoke c1
printfn "\nA static method on any type, with an argument of type C."
// D can represent any static method with the same signature.
// Methods on F and C are shown here.
let d = Delegate.CreateDelegate(typeof<D>, null, cmi3) :?> D
d.Invoke c1
let d = Delegate.CreateDelegate(typeof<D>, null, fmi3) :?> D
d.Invoke c1
printfn "\nA static method on any type, with an argument of"
printfn " that type and an argument of type C."
// D can represent any static method with one argument of the
// type the method belongs and a second argument of type C.
// In this case, the method is closed over the instance of
// supplied for the its first argument, and acts like an instance
// method. Methods on F and C are shown here.
let d = Delegate.CreateDelegate(typeof<D>, c1, cmi4) :?> D
d.Invoke c2
let test =
Delegate.CreateDelegate(typeof<D>, f1, fmi4, false)
// This final example specifies false for throwOnBindFailure
// in the call to CreateDelegate, so the variable 'test'
// contains Nothing if the method fails to bind (for
// example, if fmi4 happened to represent a method of
// some class other than F).
match test with
| :? D as d ->
d.Invoke c2
| _ -> ()
0
// This code example produces the following output:
// An instance method on any type, with an argument of type C.
// Instance method M1(C c) on C: this.id = 42, c.ID = 1491
// Instance method M1(C c) on F: c.ID = 1491
//
// An instance method on C with no arguments.
// Instance method M2() on C: this.id = 42
//
// A static method on any type, with an argument of type C.
// Static method M3(C c) on C: c.ID = 42
// Static method M3(C c) on F: c.ID = 42
//
// A static method on any type, with an argument of
// that type and an argument of type C.
// Static method M4(C c1, C c2) on C: c1.ID = 42, c2.ID = 1491
// Static method M4(F f, C c) on F: c.ID = 1491
Imports System.Reflection
Imports System.Security.Permissions
' Declare a delegate type. The object of this code example
' is to show all the methods this delegate can bind to.
'
Public Delegate Sub D(ByVal c As C)
' Declare two sample classes, C and F. Class C has an ID
' property so instances can be identified.
'
Public Class C
Private _id As Integer
Public ReadOnly Property ID() As Integer
Get
Return _id
End Get
End Property
Public Sub New(ByVal newId As Integer)
Me._id = newId
End Sub
Public Sub M1(ByVal c As C)
Console.WriteLine("Instance method M1(c As C) on C: this.id = {0}, c.ID = {1}", _
Me.id, c.ID)
End Sub
Public Sub M2()
Console.WriteLine("Instance method M2() on C: this.id = {0}", Me.id)
End Sub
Public Shared Sub M3(ByVal c As C)
Console.WriteLine("Shared method M3(c As C) on C: c.ID = {0}", c.ID)
End Sub
Public Shared Sub M4(ByVal c1 As C, ByVal c2 As C)
Console.WriteLine("Shared method M4(c1 As C, c2 As C) on C: c1.ID = {0}, c2.ID = {1}", _
c1.ID, c2.ID)
End Sub
End Class
Public Class F
Public Sub M1(ByVal c As C)
Console.WriteLine("Instance method M1(c As C) on F: c.ID = {0}", c.ID)
End Sub
Public Shared Sub M3(ByVal c As C)
Console.WriteLine("Shared method M3(c As C) on F: c.ID = {0}", c.ID)
End Sub
Public Shared Sub M4(ByVal f As F, ByVal c As C)
Console.WriteLine("Shared method M4(f As F, c As C) on F: c.ID = {0}", c.ID)
End Sub
End Class
Public Class Example5
Public Shared Sub Main()
Dim c1 As New C(42)
Dim c2 As New C(1491)
Dim f1 As New F()
Dim d As D
' Instance method with one argument of type C.
Dim cmi1 As MethodInfo = GetType(C).GetMethod("M1")
' Instance method with no arguments.
Dim cmi2 As MethodInfo = GetType(C).GetMethod("M2")
' Shared method with one argument of type C.
Dim cmi3 As MethodInfo = GetType(C).GetMethod("M3")
' Shared method with two arguments of type C.
Dim cmi4 As MethodInfo = GetType(C).GetMethod("M4")
' Instance method with one argument of type C.
Dim fmi1 As MethodInfo = GetType(F).GetMethod("M1")
' Shared method with one argument of type C.
Dim fmi3 As MethodInfo = GetType(F).GetMethod("M3")
' Shared method with an argument of type F and an
' argument of type C.
Dim fmi4 As MethodInfo = GetType(F).GetMethod("M4")
Console.WriteLine(vbLf & "An instance method on any type, with an argument of type C.")
' D can represent any instance method that exactly matches its
' signature. Methods on C and F are shown here.
'
d = CType([Delegate].CreateDelegate(GetType(D), c1, cmi1), D)
d(c2)
d = CType([Delegate].CreateDelegate(GetType(D), f1, fmi1), D)
d(c2)
Console.WriteLine(vbLf & "An instance method on C with no arguments.")
' D can represent an instance method on C that has no arguments;
' in this case, the argument of D represents the hidden first
' argument of any instance method. The delegate acts like a
' Shared method, and an instance of C must be passed each time
' it is invoked.
'
d = CType([Delegate].CreateDelegate(GetType(D), Nothing, cmi2), D)
d(c1)
Console.WriteLine(vbLf & "A Shared method on any type, with an argument of type C.")
' D can represent any Shared method with the same signature.
' Methods on F and C are shown here.
'
d = CType([Delegate].CreateDelegate(GetType(D), Nothing, cmi3), D)
d(c1)
d = CType([Delegate].CreateDelegate(GetType(D), Nothing, fmi3), D)
d(c1)
Console.WriteLine(vbLf & "A Shared method on any type, with an argument of")
Console.WriteLine(" that type and an argument of type C.")
' D can represent any Shared method with one argument of the
' type the method belongs and a second argument of type C.
' In this case, the method is closed over the instance of
' supplied for the its first argument, and acts like an instance
' method. Methods on F and C are shown here.
'
d = CType([Delegate].CreateDelegate(GetType(D), c1, cmi4), D)
d(c2)
Dim test As [Delegate] =
[Delegate].CreateDelegate(GetType(D), f1, fmi4, False)
' This final example specifies False for throwOnBindFailure
' in the call to CreateDelegate, so the variable 'test'
' contains Nothing if the method fails to bind (for
' example, if fmi4 happened to represent a method of
' some class other than F).
'
If test IsNot Nothing Then
d = CType(test, D)
d(c2)
End If
End Sub
End Class
' This code example produces the following output:
'
'An instance method on any type, with an argument of type C.
'Instance method M1(c As C) on C: this.id = 42, c.ID = 1491
'Instance method M1(c As C) on F: c.ID = 1491
'
'An instance method on C with no arguments.
'Instance method M2() on C: this.id = 42
'
'A Shared method on any type, with an argument of type C.
'Shared method M3(c As C) on C: c.ID = 42
'Shared method M3(c As C) on F: c.ID = 42
'
'A Shared method on any type, with an argument of
' that type and an argument of type C.
'Shared method M4(c1 As C, c2 As C) on C: c1.ID = 42, c2.ID = 1491
'Shared method M4(f As F, c As C) on F: c.ID = 1491
'
Tipos de parámetros compatibles y tipo de valor devuelto
Los tipos de parámetro y el tipo de valor devuelto de un delegado creado con esta sobrecarga de método deben ser compatibles con los tipos de parámetro y el tipo de valor devuelto del método que representa el delegado; los tipos no tienen que coincidir exactamente.
Un parámetro de un delegado es compatible con el parámetro correspondiente de un método si el tipo del parámetro del delegado es más restrictivo que el del método, porque así se garantiza que el argumento que se pase al delegado también se podrá pasar de forma segura al método.
De forma similar, el tipo de valor devuelto de un delegado es compatible con el tipo de valor devuelto de un método si el del método es más restrictivo que el del delegado, porque así se garantiza que el tipo de valor devuelto por el método se puede convertir con seguridad al tipo de valor devuelto del delegado.
Por ejemplo, un delegado con un parámetro de tipo Hashtable y un tipo de valor devuelto de Object puede representar un método con un parámetro de tipo Object y un valor devuelto de tipo Hashtable.
Determinar los métodos que un delegado puede representar
Otra manera útil de pensar en la flexibilidad proporcionada por la CreateDelegate(Type, Object, MethodInfo) sobrecarga es que cualquier delegado determinado puede representar cuatro combinaciones diferentes de firma de método y tipo de método (estática frente a instancia). Considere un tipo D
de delegado con un argumento de tipo C
. A continuación se describen los métodos D
que pueden representar, ignorando el tipo de valor devuelto, ya que debe coincidir en todos los casos:
D
puede representar cualquier método de instancia que tenga exactamente un argumento de tipoC
, independientemente del tipo al que pertenezca el método de instancia. Cuando CreateDelegate se llama a ,firstArgument
es una instancia del tipomethod
al que pertenece y se dice que el delegado resultante se cierra sobre esa instancia. (Trivialmente,D
también se puede cerrar en una referencia nula sifirstArgument
es una referencia nula).D
puede representar un método de instancia deC
que no tiene argumentos. Cuando CreateDelegate se llama a ,firstArgument
es una referencia nula. El delegado resultante representa un método de instancia abierta y se debe proporcionar una instancia deC
cada vez que se invoca.D
puede representar un método estático que toma un argumento de tipoC
y ese método puede pertenecer a cualquier tipo. Cuando CreateDelegate se llama a ,firstArgument
es una referencia nula. El delegado resultante representa un método estático abierto y se debe proporcionar una instancia deC
cada vez que se invoca.D
puede representar un método estático que pertenece al tipoF
y tiene dos argumentos, de tipoF
y tipoC
. Cuando CreateDelegate se llama a ,firstArgument
es una instancia deF
. El delegado resultante representa un método estático que se cierra sobre esa instancia deF
. Tenga en cuenta que en el casoF
de que yC
sean del mismo tipo, el método estático tiene dos argumentos de ese tipo. (En este caso,D
se cierra sobre una referencia nula sifirstArgument
es una referencia nula).