EventInfo.AddEventHandler(Object, Delegate) Metode
Definisi
Penting
Beberapa informasi terkait produk prarilis yang dapat diubah secara signifikan sebelum dirilis. Microsoft tidak memberikan jaminan, tersirat maupun tersurat, sehubungan dengan informasi yang diberikan di sini.
Menambahkan penanganan aktivitas ke sumber kejadian.
public:
virtual void AddEventHandler(System::Object ^ target, Delegate ^ handler);
public virtual void AddEventHandler (object target, Delegate handler);
public virtual void AddEventHandler (object? target, Delegate? handler);
public void AddEventHandler (object target, Delegate handler);
abstract member AddEventHandler : obj * Delegate -> unit
override this.AddEventHandler : obj * Delegate -> unit
Public Overridable Sub AddEventHandler (target As Object, handler As Delegate)
Public Sub AddEventHandler (target As Object, handler As Delegate)
Parameter
- target
- Object
Sumber kejadian.
- handler
- Delegate
Merangkum metode atau metode yang akan dipanggil ketika peristiwa dinaikkan oleh target.
Penerapan
Pengecualian
Kejadian ini tidak memiliki aksesor publik add
.
Handler yang diteruskan tidak dapat digunakan.
Pemanggil tidak memiliki izin akses ke anggota.
Catatan: Di .NET untuk aplikasi Bursa Windows atau Pustaka Kelas Portabel, tangkap pengecualian kelas dasar, MemberAccessException, sebagai gantinya.
Parameternya target
adalah null
dan peristiwanya tidak statis.
-atau-
EventInfo tidak dinyatakan pada target.
Catatan: Di .NET untuk aplikasi Bursa Windows atau Pustaka Kelas Portabel, tangkap Exception sebagai gantinya.
Contoh
Contoh berikut membuat instans System.Timers.Timer kelas, membuat penanganan aktivitas menggunakan rakitan dinamis, dan menghubungkan penanganan aktivitas dinamis. Semua tindakan dilakukan menggunakan pengikatan terlambat.
Instans Timer disimpan dalam variabel jenis Object, dan semua kode yang mengakses Timer melakukannya terlambat terikat. Contohnya menggunakan Type.GetEvent metode untuk mendapatkan Elapsed peristiwa, dan EventHandlerType properti untuk mendapatkan jenis delegasi untuk peristiwa tersebut.
Contohnya mendapatkan MethodInfo untuk Invoke
metode jenis delegasi dan mendapatkan tanda tangan delegasi dari MethodInfo instans. Contoh kemudian membuat rakitan dinamis dengan satu modul yang berisi satu jenis bernama Handler
dan memberi jenis static
metode (Shared
metode dalam Visual Basic) bernama DynamicHandler
yang menangani peristiwa.
Setelah jenis dinamis dibuat, contoh mendapatkan MethodInfo untuk metode yang sudah selesai dan menggunakannya untuk membuat instans delegasi. Instans ini diteruskan ke AddEventHandler metode untuk menghubungkan peristiwa. Program kemudian dijeda untuk memungkinkan acara dinaikkan.
using System;
using System.Reflection;
using System.Reflection.Emit;
public class Example
{
private static object? timer;
public static void Main()
{
// Get the Timer type.
Type t = typeof(System.Timers.Timer);
// Create an instance of the Timer type.
timer = Activator.CreateInstance(t);
// Use reflection to get the Elapsed event.
EventInfo? eInfo = t.GetEvent("Elapsed");
// In order to create a method to handle the Elapsed event,
// it is necessary to know the signature of the delegate
// used to raise the event. Reflection.Emit can then be
// used to construct a dynamic class with a static method
// that has the correct signature.
// Get the event handler type of the Elapsed event. This is
// a delegate type, so it has an Invoke method that has
// the same signature as the delegate. The following code
// creates an array of Type objects that represent the
// parameter types of the Invoke method.
//
Type? handlerType = eInfo?.EventHandlerType;
MethodInfo? invokeMethod = handlerType?.GetMethod("Invoke");
ParameterInfo[]? parms = invokeMethod?.GetParameters();
Type[] parmTypes = new Type[parms?.Length ?? 0];
for (int i = 0; i < parms?.Length; i++)
{
parmTypes[i] = parms[i].ParameterType;
}
// Use Reflection.Emit to create a dynamic assembly that
// will be run but not saved. An assembly must have at
// least one module, which in this case contains a single
// type. The only purpose of this type is to contain the
// event handler method. (You can use also dynamic methods,
// which are simpler because there is no need to create an
// assembly, module, or type.)
//
AssemblyName aName = new AssemblyName();
aName.Name = "DynamicTypes";
AssemblyBuilder ab = AssemblyBuilder.DefineDynamicAssembly(aName, AssemblyBuilderAccess.Run);
ModuleBuilder mb = ab.DefineDynamicModule(aName.Name);
TypeBuilder tb = mb.DefineType("Handler", TypeAttributes.Class | TypeAttributes.Public);
// Create the method that will handle the event. The name
// is not important. The method is static, because there is
// no reason to create an instance of the dynamic type.
//
// The parameter types and return type of the method are
// the same as those of the delegate's Invoke method,
// captured earlier.
MethodBuilder handler = tb.DefineMethod("DynamicHandler",
MethodAttributes.Public | MethodAttributes.Static,
invokeMethod?.ReturnType, parmTypes);
// Generate code to handle the event. In this case, the
// handler simply prints a text string to the console.
//
ILGenerator il = handler.GetILGenerator();
il.EmitWriteLine("Timer's Elapsed event is raised.");
il.Emit(OpCodes.Ret);
// CreateType must be called before the Handler type can
// be used. In order to create the delegate that will
// handle the event, a MethodInfo from the finished type
// is required.
Type? finished = tb.CreateType();
MethodInfo? eventHandler = finished?.GetMethod("DynamicHandler");
// Use the MethodInfo to create a delegate of the correct
// type, and call the AddEventHandler method to hook up
// the event.
if (handlerType is not null && eventHandler is not null)
{
Delegate d = Delegate.CreateDelegate(handlerType, eventHandler);
eInfo?.AddEventHandler(timer, d);
}
// Late-bound calls to the Interval and Enabled property
// are required to enable the timer with a one-second
// interval.
t.InvokeMember("Interval", BindingFlags.SetProperty, null, timer, new Object[] { 1000 });
t.InvokeMember("Enabled", BindingFlags.SetProperty, null, timer, new Object[] { true });
Console.WriteLine("Press the Enter key to end the program.");
Console.ReadLine();
}
}
/* This example produces output similar to the following:
Press the Enter key to end the program.
Timer's Elapsed event is raised.
Timer's Elapsed event is raised.
Timer's Elapsed event is raised.
*/
Imports System.Reflection
Imports System.Reflection.Emit
Public Class Example
Private Shared timer As Object
Public Shared Sub Main()
' Get the Timer type.
Dim t As Type = GetType(System.Timers.Timer)
' Create an instance of the Timer type.
timer = Activator.CreateInstance(t)
' Use reflection to get the Elapsed event.
Dim eInfo As EventInfo = t.GetEvent("Elapsed")
' In order to create a method to handle the Elapsed event,
' it is necessary to know the signature of the delegate
' used to raise the event. Reflection.Emit can then be
' used to construct a dynamic class with a static method
' that has the correct signature.
'
' Get the event handler type of the Elapsed event. This is
' a delegate type, so it has an Invoke method that has
' the same signature as the delegate. The following code
' creates an array of Type objects that represent the
' parameter types of the Invoke method.
'
Dim handlerType As Type = eInfo.EventHandlerType
Dim invokeMethod As MethodInfo = handlerType.GetMethod("Invoke")
Dim parms As ParameterInfo() = invokeMethod.GetParameters()
'
' Note that in Visual Basic you must dimension the array one
' unit smaller than the source array in order to get an array
' of the same size. This is because Visual Basic adds an extra
' element to every array, for ease of use.
'
Dim parmTypes(parms.Length - 1) As Type
Dim i As Integer
For i = 0 To parms.Length - 1
parmTypes(i) = parms(i).ParameterType
Next i
' Use Reflection.Emit to create a dynamic assembly that
' will be run but not saved. An assembly must have at
' least one module, which in this case contains a single
' type. The only purpose of this type is to contain the
' event handler method. (You can alsso use dynamic methods,
' which are simpler because there is no need to create an
' assembly, module, or type.)
Dim aName As New AssemblyName()
aName.Name = "DynamicTypes"
Dim ab As AssemblyBuilder = AssemblyBuilder.DefineDynamicAssembly(aName, AssemblyBuilderAccess.Run)
Dim mb As ModuleBuilder = ab.DefineDynamicModule(aName.Name)
Dim tb As TypeBuilder = mb.DefineType("Handler", TypeAttributes.Class Or TypeAttributes.Public)
' Create the method that will handle the event. The name
' is not important. The method is Shared ("static" in
' reflection), because there is no reason to create an
' instance of the dynamic type "Handler".
'
' The parameter types and return type of the method are
' the same as those of the delegate's Invoke method,
' captured earlier.
Dim handler As MethodBuilder = tb.DefineMethod("DynamicHandler", MethodAttributes.Public Or MethodAttributes.Static, invokeMethod.ReturnType, parmTypes)
' Generate code to handle the event. In this case, the
' handler simply prints a text string to the console.
'
Dim il As ILGenerator = handler.GetILGenerator()
il.EmitWriteLine("Timer's Elapsed event is raised.")
il.Emit(OpCodes.Ret)
' CreateType must be called before the Handler type can
' be used. In order to create the delegate that will
' handle the event, a MethodInfo from the finished type
' is required.
Dim finished As Type = tb.CreateType()
Dim eventHandler As MethodInfo = finished.GetMethod("DynamicHandler")
' Use the MethodInfo to create a delegate of the correct
' type, and call the AddEventHandler method to hook up
' the event.
Dim d As [Delegate] = [Delegate].CreateDelegate(handlerType, eventHandler)
eInfo.AddEventHandler(timer, d)
' Late-bound calls to the Interval and Enabled property
' are required to enable the timer with a one-second
' interval.
t.InvokeMember("Interval", BindingFlags.SetProperty, Nothing, timer, New [Object]() {1000})
t.InvokeMember("Enabled", BindingFlags.SetProperty, Nothing, timer, New [Object]() {True})
Console.WriteLine("Press the Enter key to end the program.")
Console.ReadLine()
End Sub
End Class
' This example produces output similar to the following:
' Press the Enter key to end the program.
' Timer's Elapsed event is raised.
' Timer's Elapsed event is raised.
' Timer's Elapsed event is raised.
Keterangan
Metode ini mencoba menambahkan delegasi untuk menyinkronkan peristiwa pada objek target.
Setiap kali peristiwa dinaikkan oleh parameter target, metode atau metode yang dienkapsulasi oleh handler dipanggil.
Anda dapat menggunakan AddEventHandler
metode saat memuat jenis setelah program dikompilasi, ketika tidak dimungkinkan untuk menggunakan sintaks C# += atau Visual Basic WithEvents
dan Handles
kata kunci untuk menghubungkan peristiwa.