Procedimiento para enlazar un delegado mediante la reflexión

Cuando se usa la reflexión para cargar y ejecutar ensamblados, no se pueden usar características del lenguaje como el operador += de C# o la instrucción AddHandler de Visual Basic para enlazar eventos. Los procedimientos siguientes muestran cómo enlazar un método existente a un evento obteniendo todos los tipos necesarios mediante reflexión y cómo crear un método dinámico utilizando la emisión de la reflexión y enlazarlo a un evento.

Nota

Para conocer otra manera de enlazar un delegado de control de eventos, vea el ejemplo de código del método AddEventHandler de la clase EventInfo.

Para enlazar un delegado mediante la reflexión

1. Cargue un ensamblado que contenga un tipo que provoque eventos. Los ensamblados normalmente se cargan con el método Assembly.Load. Para mantener la simplicidad de este ejemplo, se utiliza un formulario derivado del ensamblado actual, de manera que se utilice el método GetExecutingAssembly para cargar el ensamblado actual.

   Assembly^ assem = Example::typeid->Assembly;
   

   Assembly assem = typeof(Example).Assembly;
   

   Dim assem As Assembly = GetType(Example).Assembly
   

2. Obtenga un objeto Type que represente el tipo y cree una instancia de dicho tipo. El método CreateInstance(Type) se utiliza en el código siguiente porque el formulario tiene un constructor sin parámetros. Hay varias otras sobrecargas del método CreateInstance que puede utilizar si el tipo que está creando no tiene un constructor sin parámetros. La nueva instancia se almacena como tipo Object para mantener la ficción de que no se sabe nada sobre el ensamblado. (La reflexión le permite obtener los tipos de un ensamblado sin conocer de antemano sus nombres.)

   Type^ tExForm = assem->GetType("ExampleForm");
   Object^ exFormAsObj = Activator::CreateInstance(tExForm);
   

   Type tExForm = assem.GetType("ExampleForm");
   Object exFormAsObj = Activator.CreateInstance(tExForm);
   

   Dim tExForm As Type = assem.GetType("ExampleForm")
   Dim exFormAsObj As Object = _
       Activator.CreateInstance(tExForm)
   

3. Obtenga un objeto EventInfo que represente el evento y utilice la propiedad EventHandlerType para obtener el tipo de delegado utilizado para controlar el evento. En el código siguiente, se obtiene EventInfo para el evento Click.

   EventInfo^ evClick = tExForm->GetEvent("Click");
   Type^ tDelegate = evClick->EventHandlerType;
   

   EventInfo evClick = tExForm.GetEvent("Click");
   Type tDelegate = evClick.EventHandlerType;
   

   Dim evClick As EventInfo = tExForm.GetEvent("Click")
   Dim tDelegate As Type = evClick.EventHandlerType
   

4. Obtenga un objeto MethodInfo que representa el método que controla el evento. El código del programa completo de la sección Ejemplo, que se encuentra más adelante en este artículo, contiene un método que coincide con la signatura del delegado EventHandler, que controla el evento Click, pero también puede generar métodos dinámicos en tiempo de ejecución. Para obtener detalles, vea el procedimiento de acompañamiento para generar un controlador de eventos en tiempo de ejecución usando un método dinámico.

   MethodInfo^ miHandler =
       Type::GetType("Example")->GetMethod("LuckyHandler",
           BindingFlags::NonPublic | BindingFlags::Instance);
   

   MethodInfo miHandler =
       typeof(Example).GetMethod("LuckyHandler",
           BindingFlags.NonPublic | BindingFlags.Instance);
   

   Dim miHandler As MethodInfo = _
       GetType(Example).GetMethod("LuckyHandler", _
           BindingFlags.NonPublic Or BindingFlags.Instance)
   

5. Cree una instancia del delegado utilizando el método CreateDelegate. Este método es estático (Shared en Visual Basic), por lo que se debe proporcionar el tipo de delegado. Se recomienda utilizar las sobrecargas de CreateDelegate que toman MethodInfo.

   Delegate^ d = Delegate::CreateDelegate(tDelegate, this, miHandler);
   

   Delegate d = Delegate.CreateDelegate(tDelegate, this, miHandler);
   

   Dim d As [Delegate] = _
       [Delegate].CreateDelegate(tDelegate, Me, miHandler)
   

6. Obtenga el método del descriptor de acceso add e invóquelo para enlazar el evento. Todos los eventos tienen un descriptor de acceso add y un descriptor de acceso remove, que son ocultados por la sintaxis de los lenguajes de alto nivel. Por ejemplo, C# usa el operador += para enlazar eventos y Visual Basic usa la instrucción AddHandler. El código siguiente obtiene el descriptor de acceso add del evento Click y lo invoca enlazado en tiempo de ejecución, pasando la instancia del delegado. Los argumentos se deben pasar como una matriz.

   MethodInfo^ addHandler = evClick->GetAddMethod();
   array<Object^>^ addHandlerArgs = { d };
   addHandler->Invoke(exFormAsObj, addHandlerArgs);
   

   MethodInfo addHandler = evClick.GetAddMethod();
   Object[] addHandlerArgs = { d };
   addHandler.Invoke(exFormAsObj, addHandlerArgs);
   

   Dim miAddHandler As MethodInfo = evClick.GetAddMethod()
   Dim addHandlerArgs() As Object = {d}
   miAddHandler.Invoke(exFormAsObj, addHandlerArgs)
   

7. Pruebe el evento. El código siguiente muestra el formulario definido en el ejemplo de código. Al hacer clic en el formulario, se invoca el controlador de eventos.

   Application::Run((Form^) exFormAsObj);
   

   Application.Run((Form) exFormAsObj);
   

   Application.Run(CType(exFormAsObj, Form))
   

Generar un controlador de eventos en tiempo de ejecución utilizando un método dinámico

1. utilizando métodos dinámicos ligeros y la emisión de reflexión se pueden generar métodos de controlador de eventos en tiempo de ejecución. Para construir un controlador de eventos, es necesario conocer el tipo de valor devuelto y los tipos de parámetros del delegado. Éstos se pueden obtener examinando el método Invoke del delegado. El código siguiente utiliza los métodos GetDelegateReturnType y GetDelegateParameterTypes para obtener esta información. El código para estos métodos se puede encontrar más adelante en este artículo, en la sección Ejemplo.

   No es necesario asignar nombre a DynamicMethod, por lo que se puede utilizar la cadena vacía. En el código siguiente, el último argumento asocia el método dinámico con el tipo actual, dando al delegado acceso a todos los miembros públicos y privados de la clase Example.

   Type^ returnType = GetDelegateReturnType(tDelegate);
   if (returnType != void::typeid)
       throw gcnew ApplicationException("Delegate has a return type.");
       
   DynamicMethod^ handler =
       gcnew DynamicMethod("",
                         nullptr,
                         GetDelegateParameterTypes(tDelegate),
                         Example::typeid);
   

   Type returnType = GetDelegateReturnType(tDelegate);
   if (returnType != typeof(void))
       throw new ArgumentException("Delegate has a return type.", nameof(d));
   
   DynamicMethod handler =
       new DynamicMethod("",
                         null,
                         GetDelegateParameterTypes(tDelegate),
                         typeof(Example));
   

   Dim returnType As Type = GetDelegateReturnType(tDelegate)
   If returnType IsNot GetType(Void) Then
       Throw New ArgumentException("Delegate has a return type.", NameOf(d))
   End If
   
   Dim handler As New DynamicMethod( _
       "", _
       Nothing, _
       GetDelegateParameterTypes(tDelegate), _
       GetType(Example) _
   )
   

2. Genere un cuerpo del método. Este método carga una cadena, llama a la sobrecarga del método MessageBox.Show que toma una cadena, saca el valor devuelto de la pila (porque el controlador no tiene tipo de valor devuelto) y vuelve. Para más información sobre cómo emitir métodos dinámicos, vea Cómo: Definir y ejecutar métodos dinámicos.

   ILGenerator^ ilgen = handler->GetILGenerator();
   
   array<Type^>^ showParameters = { String::typeid };
   MethodInfo^ simpleShow =
       MessageBox::typeid->GetMethod("Show", showParameters);
   
   ilgen->Emit(OpCodes::Ldstr,
       "This event handler was constructed at run time.");
   ilgen->Emit(OpCodes::Call, simpleShow);
   ilgen->Emit(OpCodes::Pop);
   ilgen->Emit(OpCodes::Ret);
   

   ILGenerator ilgen = handler.GetILGenerator();
   
   Type[] showParameters = { typeof(String) };
   MethodInfo simpleShow =
       typeof(MessageBox).GetMethod("Show", showParameters);
   
   ilgen.Emit(OpCodes.Ldstr,
       "This event handler was constructed at run time.");
   ilgen.Emit(OpCodes.Call, simpleShow);
   ilgen.Emit(OpCodes.Pop);
   ilgen.Emit(OpCodes.Ret);
   

   Dim ilgen As ILGenerator = handler.GetILGenerator()
   
   Dim showParameters As Type() = {GetType(String)}
   Dim simpleShow As MethodInfo = _
       GetType(MessageBox).GetMethod("Show", showParameters)
   
   ilgen.Emit(OpCodes.Ldstr, _
       "This event handler was constructed at run time.")
   ilgen.Emit(OpCodes.Call, simpleShow)
   ilgen.Emit(OpCodes.Pop)
   ilgen.Emit(OpCodes.Ret)
   

3. Finalice el método dinámico llamando a su método CreateDelegate. Utilice el descriptor de acceso add para agregar el delegado a la lista de invocación del evento.

   Delegate^ dEmitted = handler->CreateDelegate(tDelegate);
   addHandler->Invoke(exFormAsObj, gcnew array<Object^> { dEmitted });
   

   Delegate dEmitted = handler.CreateDelegate(tDelegate);
   addHandler.Invoke(exFormAsObj, new Object[] { dEmitted });
   

   Dim dEmitted As [Delegate] = handler.CreateDelegate(tDelegate)
   miAddHandler.Invoke(exFormAsObj, New Object() {dEmitted})
   

4. Pruebe el evento. El código siguiente carga el formulario definido en el ejemplo de código. Al hacer clic en el formulario se invocan el controlador de eventos predefinido y el controlador de eventos emitido.

   Application::Run((Form^) exFormAsObj);
   

   Application.Run((Form) exFormAsObj);
   

   Application.Run(CType(exFormAsObj, Form))
   

Ejemplo

El siguiente ejemplo de código muestra cómo enlazar un método existente con un evento utilizando la reflexión y cómo utilizar la clase DynamicMethod para emitir un método en tiempo de ejecución y enlazarlo con un evento.

#using <System.dll>
#using <System.Windows.Forms.dll>

using namespace System;
using namespace System::Reflection;
using namespace System::Reflection::Emit;
using namespace System::Windows::Forms;

public ref class ExampleForm : public Form
{
public:
    ExampleForm() : Form()
    {
        this->Text = "Click me";
    }
};

public ref class Example
{
public:
    static void Main()
    {
        Example^ ex = gcnew Example();
        ex->HookUpDelegate();
    }

private:
    void HookUpDelegate()
    {
        // Load an assembly, for example using the Assembly.Load
        // method. In this case, the executing assembly is loaded, to
        // keep the demonstration simple.
        //
        Assembly^ assem = Example::typeid->Assembly;

        // Get the type that is to be loaded, and create an instance
        // of it. Activator::CreateInstance has other overloads, if
        // the type lacks a default constructor. The new instance
        // is stored as type Object, to maintain the fiction that
        // nothing is known about the assembly. (Note that you can
        // get the types in an assembly without knowing their names
        // in advance.)
        //
        Type^ tExForm = assem->GetType("ExampleForm");
        Object^ exFormAsObj = Activator::CreateInstance(tExForm);

        // Get an EventInfo representing the Click event, and get the
        // type of delegate that handles the event.
        //
        EventInfo^ evClick = tExForm->GetEvent("Click");
        Type^ tDelegate = evClick->EventHandlerType;

        // If you already have a method with the correct signature,
        // you can simply get a MethodInfo for it. 
        //
        MethodInfo^ miHandler =
            Type::GetType("Example")->GetMethod("LuckyHandler",
                BindingFlags::NonPublic | BindingFlags::Instance);
            
        // Create an instance of the delegate. Using the overloads
        // of CreateDelegate that take MethodInfo is recommended.
        //
        Delegate^ d = Delegate::CreateDelegate(tDelegate, this, miHandler);

        // Get the "add" accessor of the event and invoke it late-
        // bound, passing in the delegate instance. This is equivalent
        // to using the += operator in C#, or AddHandler in Visual
        // Basic. The instance on which the "add" accessor is invoked
        // is the form; the arguments must be passed as an array.
        //
        MethodInfo^ addHandler = evClick->GetAddMethod();
        array<Object^>^ addHandlerArgs = { d };
        addHandler->Invoke(exFormAsObj, addHandlerArgs);

        // Event handler methods can also be generated at run time,
        // using lightweight dynamic methods and Reflection.Emit.
        // To construct an event handler, you need the return type
        // and parameter types of the delegate. These can be obtained
        // by examining the delegate's Invoke method. 
        //
        // It is not necessary to name dynamic methods, so the empty 
        // string can be used. The last argument associates the 
        // dynamic method with the current type, giving the delegate
        // access to all the public and private members of Example,
        // as if it were an instance method.
        //
        Type^ returnType = GetDelegateReturnType(tDelegate);
        if (returnType != void::typeid)
            throw gcnew ApplicationException("Delegate has a return type.");
            
        DynamicMethod^ handler =
            gcnew DynamicMethod("",
                              nullptr,
                              GetDelegateParameterTypes(tDelegate),
                              Example::typeid);

        // Generate a method body. This method loads a string, calls 
        // the Show method overload that takes a string, pops the
        // return value off the stack (because the handler has no
        // return type), and returns.
        //
        ILGenerator^ ilgen = handler->GetILGenerator();

        array<Type^>^ showParameters = { String::typeid };
        MethodInfo^ simpleShow =
            MessageBox::typeid->GetMethod("Show", showParameters);

        ilgen->Emit(OpCodes::Ldstr,
            "This event handler was constructed at run time.");
        ilgen->Emit(OpCodes::Call, simpleShow);
        ilgen->Emit(OpCodes::Pop);
        ilgen->Emit(OpCodes::Ret);

        // Complete the dynamic method by calling its CreateDelegate
        // method. Use the "add" accessor to add the delegate to
        // the invocation list for the event.
        //
        Delegate^ dEmitted = handler->CreateDelegate(tDelegate);
        addHandler->Invoke(exFormAsObj, gcnew array<Object^> { dEmitted });

        // Show the form. Clicking on the form causes the two
        // delegates to be invoked.
        //
        Application::Run((Form^) exFormAsObj);
    }

    void LuckyHandler(Object^ sender, EventArgs^ e)
    {
        MessageBox::Show("This event handler just happened to be lying around.");
    }

    array<Type^>^ GetDelegateParameterTypes(Type^ d)
    {
        if (d->BaseType != MulticastDelegate::typeid)
            throw gcnew ApplicationException("Not a delegate.");

        MethodInfo^ invoke = d->GetMethod("Invoke");
        if (invoke == nullptr)
            throw gcnew ApplicationException("Not a delegate.");

        array<ParameterInfo^>^ parameters = invoke->GetParameters();
        array<Type^>^ typeParameters = gcnew array<Type^>(parameters->Length);
        for (int i = 0; i < parameters->Length; i++)
        {
            typeParameters[i] = parameters[i]->ParameterType;
        }
        return typeParameters;
    }

    Type^ GetDelegateReturnType(Type^ d)
    {
        if (d->BaseType != MulticastDelegate::typeid)
            throw gcnew ApplicationException("Not a delegate.");

        MethodInfo^ invoke = d->GetMethod("Invoke");
        if (invoke == nullptr)
            throw gcnew ApplicationException("Not a delegate.");

        return invoke->ReturnType;
    }
};

int main()
{
    Example::Main();
}

using System;
using System.Reflection;
using System.Reflection.Emit;
using System.Windows.Forms;

class ExampleForm : Form
{
    public ExampleForm() : base()
    {
        this.Text = "Click me";
    }
}

class Example
{
    public static void Main()
    {
        Example ex = new Example();
        ex.HookUpDelegate();
    }

    private void HookUpDelegate()
    {
        // Load an assembly, for example using the Assembly.Load
        // method. In this case, the executing assembly is loaded, to
        // keep the demonstration simple.
        //
        Assembly assem = typeof(Example).Assembly;

        // Get the type that is to be loaded, and create an instance
        // of it. Activator.CreateInstance has other overloads, if
        // the type lacks a default constructor. The new instance
        // is stored as type Object, to maintain the fiction that
        // nothing is known about the assembly. (Note that you can
        // get the types in an assembly without knowing their names
        // in advance.)
        //
        Type tExForm = assem.GetType("ExampleForm");
        Object exFormAsObj = Activator.CreateInstance(tExForm);

        // Get an EventInfo representing the Click event, and get the
        // type of delegate that handles the event.
        //
        EventInfo evClick = tExForm.GetEvent("Click");
        Type tDelegate = evClick.EventHandlerType;

        // If you already have a method with the correct signature,
        // you can simply get a MethodInfo for it.
        //
        MethodInfo miHandler =
            typeof(Example).GetMethod("LuckyHandler",
                BindingFlags.NonPublic | BindingFlags.Instance);
            
        // Create an instance of the delegate. Using the overloads
        // of CreateDelegate that take MethodInfo is recommended.
        //
        Delegate d = Delegate.CreateDelegate(tDelegate, this, miHandler);

        // Get the "add" accessor of the event and invoke it late-
        // bound, passing in the delegate instance. This is equivalent
        // to using the += operator in C#, or AddHandler in Visual
        // Basic. The instance on which the "add" accessor is invoked
        // is the form; the arguments must be passed as an array.
        //
        MethodInfo addHandler = evClick.GetAddMethod();
        Object[] addHandlerArgs = { d };
        addHandler.Invoke(exFormAsObj, addHandlerArgs);

        // Event handler methods can also be generated at run time,
        // using lightweight dynamic methods and Reflection.Emit.
        // To construct an event handler, you need the return type
        // and parameter types of the delegate. These can be obtained
        // by examining the delegate's Invoke method.
        //
        // It is not necessary to name dynamic methods, so the empty
        // string can be used. The last argument associates the
        // dynamic method with the current type, giving the delegate
        // access to all the public and private members of Example,
        // as if it were an instance method.
        //
        Type returnType = GetDelegateReturnType(tDelegate);
        if (returnType != typeof(void))
            throw new ArgumentException("Delegate has a return type.", nameof(d));

        DynamicMethod handler =
            new DynamicMethod("",
                              null,
                              GetDelegateParameterTypes(tDelegate),
                              typeof(Example));

        // Generate a method body. This method loads a string, calls
        // the Show method overload that takes a string, pops the
        // return value off the stack (because the handler has no
        // return type), and returns.
        //
        ILGenerator ilgen = handler.GetILGenerator();

        Type[] showParameters = { typeof(String) };
        MethodInfo simpleShow =
            typeof(MessageBox).GetMethod("Show", showParameters);

        ilgen.Emit(OpCodes.Ldstr,
            "This event handler was constructed at run time.");
        ilgen.Emit(OpCodes.Call, simpleShow);
        ilgen.Emit(OpCodes.Pop);
        ilgen.Emit(OpCodes.Ret);

        // Complete the dynamic method by calling its CreateDelegate
        // method. Use the "add" accessor to add the delegate to
        // the invocation list for the event.
        //
        Delegate dEmitted = handler.CreateDelegate(tDelegate);
        addHandler.Invoke(exFormAsObj, new Object[] { dEmitted });

        // Show the form. Clicking on the form causes the two
        // delegates to be invoked.
        //
        Application.Run((Form) exFormAsObj);
    }

    private void LuckyHandler(Object sender, EventArgs e)
    {
        MessageBox.Show("This event handler just happened to be lying around.");
    }

    private Type[] GetDelegateParameterTypes(Type d)
    {
        if (d.BaseType != typeof(MulticastDelegate))
            throw new ArgumentException("Not a delegate.", nameof(d));

        MethodInfo invoke = d.GetMethod("Invoke");
        if (invoke == null)
            throw new ArgumentException("Not a delegate.", nameof(d));

        ParameterInfo[] parameters = invoke.GetParameters();
        Type[] typeParameters = new Type[parameters.Length];
        for (int i = 0; i < parameters.Length; i++)
        {
            typeParameters[i] = parameters[i].ParameterType;
        }
        return typeParameters;
    }

    private Type GetDelegateReturnType(Type d)
    {
        if (d.BaseType != typeof(MulticastDelegate))
            throw new ArgumentException("Not a delegate.", nameof(d));

        MethodInfo invoke = d.GetMethod("Invoke");
        if (invoke == null)
            throw new ArgumentException("Not a delegate.", nameof(d));

        return invoke.ReturnType;
    }
}

Imports System.Reflection
Imports System.Reflection.Emit
Imports System.Windows.Forms

Class ExampleForm
    Inherits Form

    Public Sub New()
        Me.Text = "Click me"

    End Sub
End Class

Class Example
    Public Shared Sub Main()
        Dim ex As New Example()
        ex.HookUpDelegate()
    End Sub

    Private Sub HookUpDelegate()
        ' Load an assembly, for example using the Assembly.Load
        ' method. In this case, the executing assembly is loaded, to
        ' keep the demonstration simple.
        '
        Dim assem As Assembly = GetType(Example).Assembly

        ' Get the type that is to be loaded, and create an instance 
        ' of it. Activator.CreateInstance also has an overload that
        ' takes an array of types representing the types of the 
        ' constructor parameters, if the type you are creating does
        ' not have a parameterless constructor. The new instance
        ' is stored as type Object, to maintain the fiction that 
        ' nothing is known about the assembly. (Note that you can
        ' get the types in an assembly without knowing their names
        ' in advance.)
        '
        Dim tExForm As Type = assem.GetType("ExampleForm")
        Dim exFormAsObj As Object = _
            Activator.CreateInstance(tExForm)

        ' Get an EventInfo representing the Click event, and get the
        ' type of delegate that handles the event.
        '
        Dim evClick As EventInfo = tExForm.GetEvent("Click")
        Dim tDelegate As Type = evClick.EventHandlerType

        ' If you already have a method with the correct signature,
        ' you can simply get a MethodInfo for it. 
        '
        Dim miHandler As MethodInfo = _
            GetType(Example).GetMethod("LuckyHandler", _
                BindingFlags.NonPublic Or BindingFlags.Instance)
        ' Create an instance of the delegate. Using the overloads
        ' of CreateDelegate that take MethodInfo is recommended.
        '
        Dim d As [Delegate] = _
            [Delegate].CreateDelegate(tDelegate, Me, miHandler)

        ' Get the "add" accessor of the event and invoke it late-
        ' bound, passing in the delegate instance. This is equivalent
        ' to using the += operator in C#, or AddHandler in Visual
        ' Basic. The instance on which the "add" accessor is invoked
        ' is the form; the arguments must be passed as an array.
        '
        Dim miAddHandler As MethodInfo = evClick.GetAddMethod()
        Dim addHandlerArgs() As Object = {d}
        miAddHandler.Invoke(exFormAsObj, addHandlerArgs)

        ' Event handler methods can also be generated at run time,
        ' using lightweight dynamic methods and Reflection.Emit. 
        ' To construct an event handler, you need the return type
        ' and parameter types of the delegate. These can be obtained
        ' by examining the delegate's Invoke method. 
        '
        ' It is not necessary to name dynamic methods, so the empty 
        ' string can be used. The last argument associates the 
        ' dynamic method with the current type, giving the delegate
        ' access to all the public and private members of Example,
        ' as if it were an instance method.
        '
        Dim returnType As Type = GetDelegateReturnType(tDelegate)
        If returnType IsNot GetType(Void) Then
            Throw New ArgumentException("Delegate has a return type.", NameOf(d))
        End If

        Dim handler As New DynamicMethod( _
            "", _
            Nothing, _
            GetDelegateParameterTypes(tDelegate), _
            GetType(Example) _
        )

        ' Generate a method body. This method loads a string, calls 
        ' the Show method overload that takes a string, pops the 
        ' return value off the stack (because the handler has no
        ' return type), and returns.
        '
        Dim ilgen As ILGenerator = handler.GetILGenerator()

        Dim showParameters As Type() = {GetType(String)}
        Dim simpleShow As MethodInfo = _
            GetType(MessageBox).GetMethod("Show", showParameters)

        ilgen.Emit(OpCodes.Ldstr, _
            "This event handler was constructed at run time.")
        ilgen.Emit(OpCodes.Call, simpleShow)
        ilgen.Emit(OpCodes.Pop)
        ilgen.Emit(OpCodes.Ret)

        ' Complete the dynamic method by calling its CreateDelegate
        ' method. Use the "add" accessor to add the delegate to
        ' the invocation list for the event.
        '
        Dim dEmitted As [Delegate] = handler.CreateDelegate(tDelegate)
        miAddHandler.Invoke(exFormAsObj, New Object() {dEmitted})

        ' Show the form. Clicking on the form causes the two
        ' delegates to be invoked.
        '
        Application.Run(CType(exFormAsObj, Form))

    End Sub

    Private Sub LuckyHandler(ByVal sender As [Object], _
        ByVal e As EventArgs)

        MessageBox.Show("This event handler just happened to be lying around.")
    End Sub

    Private Function GetDelegateParameterTypes(ByVal d As Type) _
        As Type()

        If d.BaseType IsNot GetType(MulticastDelegate) Then
            Throw New ArgumentException("Not a delegate.", NameOf(d))
        End If

        Dim invoke As MethodInfo = d.GetMethod("Invoke")
        If invoke Is Nothing Then
            Throw New ArgumentException("Not a delegate.", NameOf(d))
        End If

        Dim parameters As ParameterInfo() = invoke.GetParameters()
        ' Dimension this array Length - 1, because VB adds an extra
        ' element to zero-based arrays.
        Dim typeParameters(parameters.Length - 1) As Type
        For i As Integer = 0 To parameters.Length - 1
            typeParameters(i) = parameters(i).ParameterType
        Next i

        Return typeParameters

    End Function


    Private Function GetDelegateReturnType(ByVal d As Type) As Type

        If d.BaseType IsNot GetType(MulticastDelegate) Then
            Throw New ArgumentException("Not a delegate.", NameOf(d))
        End If

        Dim invoke As MethodInfo = d.GetMethod("Invoke")
        If invoke Is Nothing Then
            Throw New ArgumentException("Not a delegate.", NameOf(d))
        End If

        Return invoke.ReturnType

    End Function
End Class

Vea también

• Assembly.Load
• DynamicMethod
• CreateInstance
• CreateDelegate
• Cómo: Definir y ejecutar métodos dinámicos
• Reflexión