[VB.NET][问]如何让父窗体响应子窗体中的某一个自定义事件

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[问]如何让父窗体响应子窗体中的某一个自定义事件
各位,小弟有一问题请教:

如题:
1 在子窗体中定义一个事件
2 由父窗体来响应这个自定义事件
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Public Class Form1

Private Sub aaa(ByVal str As String)
Me.Text = str
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim a As New Form2
AddHandler a.aaaaa, AddressOf Me.aaa
a.ShowDialog()

End Sub

End Class

Public Class Form2
Inherits Form

Public Event aaaaa(ByVal str As String)

Public Sub New()
Dim b As New Button
Me.Controls.Add(b)
AddHandler b.Click, AddressOf Button1_Click

End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
RaiseEvent aaaaa( dddddddddddddddddddddddddddddd )
End Sub

End Class
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