HOW TO：使用反映連結委派

發行項
08/21/2008

更新：2007 年 11 月

當您使用反映 (Reflection) 來載入及執行組件時，將無法使用類似 C# += 運算子或 Visual Basic AddHandler 陳述式的語言功能來連結事件。下列程序將示範如何透過反映取得所有必要的型別，以將現有的方法連結到事件，以及如何使用反映發出建立動態方法，並將它連結到事件。

注意事項：
如需連結事件處理委派 (Delegate) 的另一個方法，請參閱 EventInfo 類別之 AddEventHandler 方法的程式碼範例。

若要使用反映來連結委派

載入包含可引發事件之型別的組件；組件通常是利用 Assembly.Load 方法載入。為了要維持此範例的簡單性，會使用目前組件中的衍生表單，以便使用 GetExecutingAssembly 方法來載入目前的組件。
```
Dim assem As [Assembly] = [Assembly].GetExecutingAssembly()
```
```
Assembly assem = Assembly.GetExecutingAssembly();
```
取得表示此型別的 Type 物件，並建立此型別的執行個體。下列程式碼中會使用 CreateInstance(Type) 方法，因為表單有預設建構函式。如果您所建立的型別沒有預設建構函式，您可以使用數個其他的 CreateInstance 方法多載。新的執行個體會儲存為型別 Object，以維護對組件一無所知的假定。(反映可讓您取得組件中的型別，而不需要事先知道其名稱)。
```
Dim tExForm As Type = assem.GetType("ExampleForm")
Dim exFormAsObj As Object = _
    Activator.CreateInstance(tExForm)
```
```
Type tExForm = assem.GetType("ExampleForm");
Object exFormAsObj = Activator.CreateInstance(tExForm);
```

取得表示此事件的 EventInfo 物件，並使用 EventHandlerType 屬性來取得用來處理此事件的委派型別。在下列程式碼中，會取得 Click 事件的 EventInfo。

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

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

取得 MethodInfo 物件，其表示處理事件的方法。這個主題之後的範例一節中的完整程式碼，包含了與 EventHandler 委派的簽章符合的方法，此委派可處理 Click 事件，但是您也可以在執行階段產生動態方法。如需詳細資訊，請參閱若要在執行階段使用動態方法來產生事件處理常式的程序。
```
Dim miHandler As MethodInfo = _
    GetType(Example).GetMethod("LuckyHandler", _
        BindingFlags.NonPublic Or BindingFlags.Instance)
```
```
MethodInfo miHandler = 
    typeof(Example).GetMethod("LuckyHandler", 
        BindingFlags.NonPublic | BindingFlags.Instance);
```
使用 CreateDelegate 方法建立此委派的執行個體。這個方法為靜態 (Visual Basic 中為 Shared)，所以必須提供委派型別。建議使用可接受 MethodInfo 的 CreateDelegate 多載。
```
Dim d As [Delegate] = _
    [Delegate].CreateDelegate(tDelegate, Me, miHandler)
```
```
Delegate d = Delegate.CreateDelegate(tDelegate, this, miHandler);
```
取得 add 存取子方法，並叫用它來連結事件。所有的事件都有 add 存取子和 remove 存取子，這兩個存取子會由高階語言的語法所隱藏。例如，C# 會使用 += 運算子來連結事件，而 Visual Basic 則會使用 AddHandler 陳述式。下列程式碼會取得 Click 事件的 add 存取子，並以晚期繫結的形式來叫用它，傳入委派執行個體；引數必須以陣列的形式傳遞。
```
Dim miAddHandler As MethodInfo = evClick.GetAddMethod()
Dim addHandlerArgs() As Object = { d }
miAddHandler.Invoke(exFormAsObj, addHandlerArgs)
```
```
MethodInfo addHandler = evClick.GetAddMethod();
Object[] addHandlerArgs = { d };
addHandler.Invoke(exFormAsObj, addHandlerArgs);
```
測試事件。下列程式碼將顯示此程式碼範例中所定義的表單；按一下表單，即可叫用事件處理常式。
```
Application.Run(CType(exFormAsObj, Form))
```
```
Application.Run((Form) exFormAsObj);
```

若要在執行階段使用動態方法來產生事件處理常式

可以在執行階段產生事件處理常式方法，其方式是使用輕量型動態方法和反映發出。若要建構事件處理常式，您需要此委派的傳回型別和參數型別；可以藉由檢查此委派的 Invoke 方法來取得這些型別。下列程式碼使用 GetDelegateReturnType 和 GetDelegateParameterTypes 方法來取得這項資訊，而這些方法的程式碼則可以在這個主題之後的範例一節中找到。

不需要命名 DynamicMethod，所以可以使用空字串。在下列程式碼中，最後一個引數會將動態方法與目前的型別產生關聯，將委派存取提供給 Example 類別的所有公用和私用成員。
```
Dim returnType As Type = GetDelegateReturnType(tDelegate)
If returnType IsNot GetType(Void) Then
    Throw New ApplicationException("Delegate has a return type.")
End If

Dim handler As New DynamicMethod( _
    "", _
    Nothing, _
    GetDelegateParameterTypes(tDelegate), _
    GetType(Example) _
)
```
```
Type returnType = GetDelegateReturnType(tDelegate);
if (returnType != typeof(void))
    throw new ApplicationException("Delegate has a return type.");

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

產生方法主體。這個方法會載入字串、呼叫可接受字串之 MessageBox.Show 方法的多載，將傳回值從堆疊中移除 (因為處理常式沒有傳回型別)，然後傳回。若要進一步了解有關發出動態方法，請參閱 HOW TO：定義和執行動態方法。

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)

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);

完成動態方法，其方式是呼叫它的 CreateDelegate 方法。使用 add 存取子，將此委派加入到事件的引動過程清單中。

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

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

測試事件。下列程式碼將載入此程式碼範例中所定義的表單；按一下表單可叫用預先定義的事件處理常式和發出的事件處理常式兩者。
```
Application.Run(CType(exFormAsObj, Form))
```
```
Application.Run((Form) exFormAsObj);
```

範例

下列程式碼範例將示範如何使用反映，將現有的方法與事件連結，也將示範如何使用 DynamicMethod 類別於執行階段發出方法，並將它與事件連結。

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

Class ExampleForm
    Inherits Form

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

    End Sub 'New
End Class 'ExampleForm

Class Example

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

    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] = [Assembly].GetExecutingAssembly()

        ' 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 ApplicationException("Delegate has a return type.")
        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 ApplicationException("Not a delegate.")
        End If

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

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

        Return invoke.ReturnType

    End Function 
End Class

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 = Assembly.GetExecutingAssembly();

        // 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 ApplicationException("Delegate has a return type.");

        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 ApplicationException("Not a delegate.");

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

        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 ApplicationException("Not a delegate.");

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

        return invoke.ReturnType;
    }
}

編譯程式碼

此程式碼含有進行編譯所需的 C# using 陳述式 (Visual Basic 中的 Imports)。
從命令列進行編譯並不需要額外的組件參考；在 Visual Studio 中，您必須將參考加入到 System.Windows.Forms.dll，因為此範例為主控台應用程式。
使用 csc.exe、vbc.exe 或 cl.exe，在命令列上編譯程式碼；若要在 Visual Studio 中編譯程式碼，請將它放置在主控台應用程式專案範本中。

請參閱

共用方式為

HOW TO：使用反映連結委派

若要使用反映來連結委派

若要在執行階段使用動態方法來產生事件處理常式

範例

編譯程式碼

請參閱

工作

參考

其他資源

其他資源