Metode System.Delegate.CreateDelegate
Artikel ini menyediakan keterangan tambahan untuk dokumentasi referensi untuk API ini.
Metode CreateDelegate membuat delegasi dari jenis tertentu.
metode CreateDelegate(Type, MethodInfo)
Kelebihan beban metode ini setara dengan memanggil CreateDelegate(Type, MethodInfo, Boolean) metode kelebihan beban dan menentukan true untuk throwOnBindFailure.
Contoh
Bagian ini berisi dua contoh kode. Contoh pertama menunjukkan dua jenis delegasi yang dapat dibuat dengan kelebihan metode ini: membuka melalui metode instans dan membuka melalui metode statis.
Contoh kode kedua menunjukkan jenis parameter yang kompatibel dan jenis pengembalian.
Contoh 1
Contoh kode berikut menunjukkan dua cara delegasi dapat dibuat menggunakan kelebihan metode CreateDelegate ini.
Catatan
Ada dua kelebihan beban CreateDelegate metode yang menentukan MethodInfo tetapi bukan argumen pertama; fungsionalitasnya sama kecuali yang satu memungkinkan Anda untuk menentukan apakah akan melemparkan kegagalan untuk mengikat, dan yang lain selalu melemparkan. Contoh kode ini menggunakan kedua kelebihan beban.
Contoh mendeklarasikan kelas C dengan metode M2 statis dan metode M1instans , dan dua jenis delegasi: D1 mengambil instans C dan string, dan D2 mengambil string.
Kelas kedua bernama Example berisi kode yang membuat delegasi.
- Delegasi jenis
D1, yang mewakili metode instans terbuka, dibuat untuk metodeM1instans . Instans harus diteruskan saat delegasi dipanggil. - Delegasi jenis
D2, yang mewakili metode statis terbuka, dibuat untuk metodeM2statis .
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!
'
Contoh 2
Contoh kode berikut menunjukkan kompatibilitas jenis parameter dan jenis pengembalian.
Contoh kode mendefinisikan kelas dasar bernama Base dan kelas bernama Derived yang berasal dari Base. Kelas turunan memiliki static metode (Shared dalam Visual Basic) yang dinamai MyMethod dengan satu parameter jenis Base dan jenis Derivedpengembalian . Contoh kode juga menentukan delegasi bernama Example yang memiliki satu parameter jenis Derived dan jenis pengembalian .Base
Contoh kode menunjukkan bahwa delegasi bernama Example dapat digunakan untuk mewakili metode MyMethod. Metode dapat terikat ke delegasi karena:
- Jenis parameter delegasi (
Derived) lebih ketat daripada jenisMyMethodparameter (Base), sehingga selalu aman untuk meneruskan argumen delegasi keMyMethod. - Jenis
MyMethodpengembalian (Derived) lebih ketat daripada jenis parameter delegasi (Base), sehingga selalu aman untuk mentransmisikan jenis pengembalian metode ke jenis pengembalian delegasi.
Contoh kode tidak menghasilkan output.
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
Metode CreateDelegate(Type, Object, MethodInfo) dan CreateDelegate(Type, Object, MethodInfo, Boolean)
Fungsionalitas kedua kelebihan beban ini sama kecuali yang satu memungkinkan Anda menentukan apakah akan melemparkan kegagalan untuk mengikat, dan yang lain selalu melempar.
Jenis delegasi dan metode harus memiliki jenis pengembalian yang kompatibel. Artinya, jenis method pengembalian harus dapat ditetapkan ke jenis pengembalian .type
firstArgument, parameter kedua untuk kelebihan beban ini, adalah argumen pertama dari metode yang diwakili delegasi. Jika firstArgument disediakan, itu diteruskan ke method setiap kali delegasi dipanggil; firstArgument dikatakan terikat ke delegasi, dan delegasi dikatakan ditutup atas argumen pertamanya. Jika method adalah static (Shared di Visual Basic), daftar argumen yang disediakan saat memanggil delegasi menyertakan semua parameter kecuali yang pertama; jika method adalah metode instans, maka firstArgument diteruskan ke parameter instans tersembunyi (diwakili oleh this dalam C#, atau oleh Me di Visual Basic).
Jika firstArgument disediakan, parameter method pertama harus merupakan jenis referensi, dan firstArgument harus kompatibel dengan jenis tersebut.
Penting
Jika method adalah static (Shared di Visual Basic) dan parameter pertamanya berjenis Object atau ValueType, maka firstArgument bisa menjadi jenis nilai. Dalam hal firstArgument ini secara otomatis dikotak. Tinju otomatis tidak terjadi untuk argumen lain, seperti dalam panggilan fungsi C# atau Visual Basic.
Jika firstArgument merupakan referensi null dan method merupakan metode instans, hasilnya tergantung pada tanda tangan jenis type delegasi dan dari method:
- Jika tanda tangan
typesecara eksplisit menyertakan parameter pertama tersembunyi ,methoddelegasi dikatakan mewakili metode instans terbuka. Ketika delegasi dipanggil, argumen pertama dalam daftar argumen diteruskan ke parameter instans tersembunyi darimethod. - Jika tanda tangan
methoddantypecocok (yaitu, semua jenis parameter kompatibel), maka delegasi dikatakan ditutup melalui referensi null. Memanggil delegasi seperti memanggil metode instans pada instans null, yang bukan hal yang sangat berguna untuk dilakukan.
Jika firstArgument merupakan referensi null dan method statis, hasilnya tergantung pada tanda tangan jenis type delegasi dan dari method:
- Jika tanda tangan
methoddantypecocok (yaitu, semua jenis parameter kompatibel), delegasi dikatakan mewakili metode statis terbuka. Ini adalah kasus yang paling umum untuk metode statis. Dalam hal ini, Anda bisa mendapatkan performa yang sedikit lebih baik dengan menggunakan CreateDelegate(Type, MethodInfo) metode kelebihan beban. - Jika tanda tangan
typedimulai dengan parametermethodkedua dan jenis parameter lainnya kompatibel, maka delegasi dikatakan ditutup melalui referensi null. Ketika delegasi dipanggil, referensi null diteruskan ke parameter pertama .method
Contoh
Contoh kode berikut menunjukkan semua metode yang dapat diwakili oleh satu jenis delegasi: ditutup melalui metode instans, membuka melalui metode instans, membuka metode statis, dan menutup metode statis.
Contoh kode mendefinisikan dua kelas, C dan F, dan jenis D delegasi dengan satu argumen jenis C. Kelas memiliki metode statis dan instans M1yang cocok , , M3dan M4, dan kelas C juga memiliki metode M2 instans yang tidak memiliki argumen.
Kelas ketiga bernama Example berisi kode yang membuat delegasi.
- Delegasi dibuat untuk metode
M1jenisCdan jenisFinstans ; masing-masing ditutup atas instans jenis masing-masing. MetodeM1jenisCmenampilkan properti instansIDterikat dan argumen. - Delegasi dibuat untuk metode
M2jenisC. Ini adalah delegasi instans terbuka, di mana argumen delegasi mewakili argumen pertama tersembunyi pada metode instans. Metode ini tidak memiliki argumen lain. Ini disebut seolah-olah itu adalah metode statis. - Delegasi dibuat untuk metode
M3statis jenisCdan jenisF; ini adalah delegasi statis terbuka. - Akhirnya, delegasi dibuat untuk metode
M4statis jenisCdan jenisF; setiap metode memiliki jenis deklarasikan sebagai argumen pertamanya, dan instans jenis disediakan, sehingga delegasi ditutup di atas argumen pertama mereka. MetodeM4jenisCmenampilkan properti instansIDterikat dan argumen.
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
'
Jenis parameter yang kompatibel dan jenis pengembalian
Jenis parameter dan jenis pengembalian delegasi yang dibuat menggunakan kelebihan beban metode ini harus kompatibel dengan jenis parameter dan jenis pengembalian metode yang diwakili delegasi; jenis tidak harus sama persis.
Parameter delegasi kompatibel dengan parameter metode yang sesuai jika jenis parameter delegasi lebih ketat daripada jenis parameter metode, karena ini menjamin bahwa argumen yang diteruskan ke delegasi dapat diteruskan dengan aman ke metode.
Demikian pula, jenis pengembalian delegasi kompatibel dengan jenis pengembalian metode jika jenis pengembalian metode lebih ketat daripada jenis pengembalian delegasi, karena ini menjamin bahwa nilai pengembalian metode dapat ditransmisikan dengan aman ke jenis pengembalian delegasi.
Misalnya, delegasi dengan parameter jenis Hashtable dan jenis Object pengembalian dapat mewakili metode dengan parameter jenis Object dan nilai pengembalian jenis Hashtable.
Menentukan metode yang dapat diwakili delegasi
Cara lain yang berguna untuk memikirkan fleksibilitas yang disediakan oleh CreateDelegate(Type, Object, MethodInfo) kelebihan beban adalah bahwa setiap delegasi tertentu dapat mewakili empat kombinasi berbeda dari tanda tangan metode dan jenis metode (statis versus instans). Pertimbangkan jenis D delegasi dengan satu argumen jenis C. Berikut ini menjelaskan metode D yang dapat diwakili, mengabaikan jenis pengembalian karena harus cocok dalam semua kasus:
Ddapat mewakili metode instans apa pun yang memiliki satu argumen jenisC, terlepas dari jenis metode instans. Ketika CreateDelegate dipanggil,firstArgumentadalah instans jenismethodmilik, dan delegasi yang dihasilkan dikatakan ditutup atas instans tersebut. (Secara trivial,Djuga dapat ditutup melalui referensi null jikafirstArgumentmerupakan referensi null.)Ddapat mewakili metodeCinstans yang tidak memiliki argumen. Ketika CreateDelegate dipanggil,firstArgumentadalah referensi null. Delegasi yang dihasilkan mewakili metode instans terbuka, dan instansCharus disediakan setiap kali dipanggil.Ddapat mewakili metode statis yang mengambil satu argumen jenisC, dan metode tersebut dapat termasuk dalam jenis apa pun. Ketika CreateDelegate dipanggil,firstArgumentadalah referensi null. Delegasi yang dihasilkan mewakili metode statis terbuka, dan instansCharus disediakan setiap kali dipanggil.Ddapat mewakili metode statis milik jenisFdan memiliki dua argumen, dari jenisFdan jenisC. Ketika CreateDelegate dipanggil,firstArgumentadalah instans dariF. Delegasi yang dihasilkan mewakili metode statis yang ditutup di atas instans tersebut dariF. Perhatikan bahwa dalam kasus di manaFdanCmerupakan jenis yang sama, metode statis memiliki dua argumen dari jenis tersebut. (Dalam hal ini,Dditutup melalui referensi null jikafirstArgumentmerupakan referensi null.)
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