.net - 如何检查 Sub 是否正在处理非自定义事件？

Question

对于自定义事件，我可以像这样检查处理程序:

 If Object.EventNameEvent Is Nothing Then
    MsgBox("Is not handling it.")
 End If

...但是我如何做同样的事情，例如，检查设计器中生成的按钮的“.click”事件？这不起作用:

If Button1.ClickEvent Is Nothing Then
   MsgBox("Is not handling it.")
End If

UPDATE

我的要求示例:

    MsgBox(HasAttachedHandler(MySub, Button1.Click))  ' Expected result: True
    MsgBox(HasAttachedHandler(MyFunc, Button1.Click)) ' Expected result: False

Private Sub MySub() Handles Button1.Click, Button2.Click
    ' bla bla bla
End Sub

Private Function MyFunc() Handles Button2.Click
    ' bla bla bla
End Function

UPDATE 2:

我正在尝试使用@ 瓦罗卡巴斯解决方案，但并没有完全满足我的需求，因此我尝试进行必要的修改以使其正常工作。问题是事件“FontChaged”没有返回想要的结果，你可以在这里看到:

    Public Class Form1

    Private WithEvents Button1 As New Button

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        ' This is working (Result True):
        MsgBox(HasAttachedHandler(Button1, "Click", "Button1_Click")) ' Result: True

        ' This is not working (Result False):
        MsgBox(HasAttachedHandler(Button1, "FontChanged", "Button1_Click")) ' Expected result: True
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles _
                Button1.Click, _
                Button1.MouseHover, _
                Button1.GotFocus, _
                Button1.Enter, _
                Button1.FontChanged, _
                Button1.AutoSizeChanged

    End Sub

    Private Function HasAttachedHandler(ByVal ctl As Control, ByVal eventname As String, ByVal targetMethod As String) As Boolean

        For Each evnt In ctl.GetType().GetEvents()

            ' Get secret key for the current event:
            Dim curEvent As Reflection.FieldInfo = GetType(Control).GetField("Event" & evnt.Name, Reflection.BindingFlags.NonPublic Or Reflection.BindingFlags.Static)

            If (curEvent IsNot Nothing) Then
                Dim secret As Object = curEvent.GetValue(Nothing)

                ' Retrieve the current event:
                Dim eventsProp As Reflection.PropertyInfo = GetType(System.ComponentModel.Component).GetProperty("Events", Reflection.BindingFlags.NonPublic Or Reflection.BindingFlags.Instance)
                Dim events As System.ComponentModel.EventHandlerList = DirectCast(eventsProp.GetValue(ctl, Nothing), System.ComponentModel.EventHandlerList)

                If (Not IsNothing(events(secret))) AndAlso curEvent.Name.ToLower = "event" & eventname.ToLower Then
                    Dim handler As [Delegate] = events(secret)
                    Dim method As Reflection.MethodInfo = handler.Method
                    If (targetMethod = method.Name) Then Return True
                End If
            End If
        Next

        Return False
    End Function

End Class

Answer 1

这是我对@HansPassant 发布的代码进行转换和修改的尝试:

Imports System.Reflection
Imports System.ComponentModel
Public Class Form1

    Private WithEvents btnA As New Button
    Private WithEvents btnB As New Button

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        btnA.AutoSize = True
        btnA.Text = "Handler Attached"
        btnA.Location = New Point(10, 10)
        Me.Controls.Add(btnA)

        btnB.AutoSize = True
        btnB.Text = "No Handlers Attached"
        Dim pt As Point = btnA.Location
        pt.Offset(btnA.Width, 0)
        btnB.Location = pt
        Me.Controls.Add(btnB)
    End Sub

    Private Sub btnA_Click(sender As Object, e As System.EventArgs) Handles btnA.Click
        Dim btnA_Handled As Boolean = HasAttachedHandler("Click", btnA)
        Dim btnB_Handled As Boolean = HasAttachedHandler("Click", btnB)

        Debug.Print("btnA_Handled = " & btnA_Handled)
        Debug.Print("btnB_Handled = " & btnB_Handled)
    End Sub

    Private Function HasAttachedHandler(ByVal EventName As String, ByVal ctl As Control) As Boolean
        ' Get secret click event key
        Dim eventClick As FieldInfo = GetType(Control).GetField("Event" & EventName, BindingFlags.NonPublic Or BindingFlags.Static)
        Dim secret As Object = eventClick.GetValue(Nothing)
        ' Retrieve the click event
        Dim eventsProp As PropertyInfo = GetType(Component).GetProperty("Events", BindingFlags.NonPublic Or BindingFlags.Instance)
        Dim events As EventHandlerList = DirectCast(eventsProp.GetValue(ctl, Nothing), EventHandlerList)
        Return Not IsNothing(events(secret))
    End Function

End Class