Creating custom events with custom EventArgs in

Posted on 2009-05-05
Last Modified: 2012-05-06
I have an application where I would like to create an event system that will pass a custom event argument to a series of form controls.

Essentially, this is meant to be a rudimentary access control mechanism. The custom argument will contain an object that will indicate a requested access level and each control will then take actions based on the values in the passed event argument.

I was looking into defining a custom event (see attached snippet), but I am not quite sure how to wire all this up.

A couple of questions:

1) Is this do-able? Can an entire class be passed as an event argument?
2) Will a disabled control still be able to receive a custom event message?
3) Can all my controls respond to the same custom event at the same time?
4)  How do I wire all this up?

I was thinking about deriving control classes from each of the UI control types I will be using so that I can define the custom event handler for each UI control from within the derived control class. I could add the handler when I create an instance of the control and remove it on disposal. Does that make sense?

Public Enum AccessLevels As Integer

    Guest    ' Read Only access (and non-SSN reports)

    Staff  ' Team Managers & Staff

    Physician    ' Area Managers

    Administrator         ' Administrator

End Enum

Public Class AccessToken

    Private _AccessLevel As AccessLevels

    Public Property AccessLevel() As AccessLevels


            Return _AccessLevel

        End Get

        Set(ByVal value As AccessLevels)

            _AccessLevel = value

        End Set

    End Property

    Public Sub New(ByVal Level As AccessLevels)

        AccessLevel = Level

    End Sub

End Class

Public Class MyEventArg

        Inherits EventArgs

        Private _Token As AccessToken

        Public Property Token() As AccessToken


                Return _Token

            End Get

            Set(ByVal value As AccessToken)

                _Token = value

            End Set

        End Property

    End Class

Public Custom Event AccessLevelEvent As EventHandler

        AddHandler(ByVal d As EventHandler)

        End AddHandler

        RemoveHandler(ByVal d As EventHandler)

        End RemoveHandler

        RaiseEvent(ByVal sender As Object, ByVal e As MyEventArg)

        End RaiseEvent

    End Event

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Question by:kkamm
  • 2
  • 2
LVL 85

Accepted Solution

Mike Tomlinson earned 500 total points
Comment Utility
Let's answer those questions...

It makes perfect sense and is completely "do-able".  =)
You can pass ANYTHING in a custom event...and pass more than one parameter if desired (it is, after all, a "custom" event!).

A disabled control will still receive custom just typically won't receive USER input from the mouse/keyboard.

Yes..ALL subscribers to an event will be notified when it is just can't predict the ORDER in which they will be notified.

I think you already nailed it...use AddHandler() when you create the controls.

A simple example of a custom event passing non-standard parameters:
Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim sc As New SomeClass

        AddHandler sc.SomeEvent, AddressOf sc_SomeEvent


    End Sub

    Private Sub sc_SomeEvent(ByVal Priority As Integer, ByVal data As SomeData)

        Dim msg As String = String.Join(" ", New String() {data.a, data.b, data.c})

        MessageBox.Show(msg, Priority.ToString)

    End Sub

End Class

Public Class SomeClass

    Public Event SomeEvent(ByVal Priority As Integer, ByVal data As SomeData)

    Public Sub SomeSub()

        RaiseEvent SomeEvent(411, New SomeData("Idle_Mind", "was", "here"))

    End Sub

End Class

Public Class SomeData

    Public a, b, c As String

    Public Sub New(ByVal a As String, ByVal b As String, ByVal c As String)

        Me.a = a

        Me.b = b

        Me.c = c

    End Sub

End Class

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Author Comment

Comment Utility
Thanks for the input, Idle Mind.

Have you dealt with this in a WPF context by any chance?
LVL 85

Expert Comment

by:Mike Tomlinson
Comment Utility
I have not played with WPF at all unfortunately...   =\

Author Comment

Comment Utility
This will ultimately be used in a WPF context, so I have to do this via routed events, but I don't think the basic functionality should be much different.

At any rate, the question was essentially answered for me. Thanks for the assist.

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