Possible to ignore base class event handler?

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Cride - 06 Mar 2008 11:34 GMT

Hello,

I have this form Form_Report_Vacations which is inherited from
Form_Report_Shifts.
Form_Report_Shifts contains an event handler for a button named
cmd_Show.

In my inherited form i want to specify different behaviour for the
click event of the button.
I dont want the code that lies in the base class to execute at all.

I have done this in the base class event handler:

---------------------------------------------------------------------------------------------------------------
Private Sub cmd_Show_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles cmd_Show.Click

' Exit sub if not in base class.
If CType(sender, Control).FindForm.Name <> "Form_Report_Shifts" Then
Exit Sub
End If

' More code
...
...

End Sub
---------------------------------------------------------------------------------------------------------------

This certainly works but it looks a little bit ugly in my opinion.
Is there a better way than this to prevent execution of code in the
event handler of the base class?

- Christian

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rowe_newsgroups - 06 Mar 2008 13:58 GMT

> Hello,
>
[quoted text clipped - 30 lines]
>
> - Christian

You need to mark your event handler method as protected overridable.
Then in the class that inherits your base page you override that
method and remove the MyBase.cmd_Show_Click() call and replace it with
your own code.

Let me know if you need a sample.

Thanks,

Seth Rowe [MVP]

Reply to this Message

cride83@gmail.com - 06 Mar 2008 18:35 GMT

> > Hello,
>
[quoted text clipped - 41 lines]
>
> Seth Rowe [MVP]

Hello,

Thanks for your answer.

I tried the thing you suggested and it worked. The code in the base
class event handler was not called.
The event handler in the inherited class, however, seemed to be firing
twice.
This was solved by removing the handler implicitly in the
Form_Child.Designer.vb file
and then adding it again.

I don't know if this is something you always have to do
as to prevent the event handler in the inherited class to be fired
twice.

Thanks.

- Christian

Reply to this Message

Tom Shelton - 06 Mar 2008 19:58 GMT

>> > Hello,
>>
[quoted text clipped - 61 lines]
>
> - Christian

Christian,

I think I would organize the code slightly differently. In the base
form, I would do something more like:

Public Class BaseForm
    Inherits System.Windows.Forms.Form

    ....

    Private Sub cmd_Show_Click (ByVal sender As Object, ByVal e As
    System.EventArgs) Handles cmd_Show.Click

        OnCmdShowClick ()

    End Sub

    Protected Overridable Sub OnCmdShowClick ()
        ' Default base implementation
    End Sub
End Sub

Public Class Derived
    Inherits BaseForm

    Protected Overrides Sub OnCmdShowClick()
    ' derived class implementation
    End Sub
End Class

I think this will solve your problem of the double event.

Signature

Tom Shelton

Reply to this Message

cride83@gmail.com - 06 Mar 2008 20:24 GMT

On 6 maalis, 21:58, Tom Shelton
<tom_shel...@YOUKNOWTHEDRILLcomcast.net> wrote:

> >> > Hello,
>
[quoted text clipped - 96 lines]
> --
> Tom Shelton

I tried this approach, thus removing the call to RemoveHandler, but
the event is still fireing twice.

The only thing that has worked yet is the following
------------------------------------------------------------------------
' Form_Report_Vacations.Designer.vb ( The derived form )
Private Sub InitializeComponent()
RemoveHandler cmd_Show.Click, AddressOf cmd_Show_Click
End Sub
------------------------------------------------------------------------

Maybe im still missing something.

- Christian

Reply to this Message

Tom Shelton - 06 Mar 2008 20:34 GMT

> On 6 maalis, 21:58, Tom Shelton
><tom_shel...@YOUKNOWTHEDRILLcomcast.net> wrote:
[quoted text clipped - 102 lines]
> I tried this approach, thus removing the call to RemoveHandler, but
> the event is still fireing twice.

Hmmm... I don't get that behavior here. Are you sure you tried the
above method (or similoar)? Can you post a more complete listing of the
derived forms code?

Signature

Tom Shelton

Reply to this Message

cride83@gmail.com - 06 Mar 2008 20:42 GMT

On 6 maalis, 22:34, Tom Shelton
<tom_shel...@YOUKNOWTHEDRILLcomcast.net> wrote:

> > On 6 maalis, 21:58, Tom Shelton
> ><tom_shel...@YOUKNOWTHEDRILLcomcast.net> wrote:
[quoted text clipped - 109 lines]
> --
> Tom Shelton

Ok,

I made a simple test with two forms. Form_Base and Form_Child.

Form_Base has a button to open the Form_Child form. Form_Base also
has button that displays a message, "From base".
The child form overrides this method and shows "From child".

It is this "From child" message that is displayed twice for some
reason.
Here's some code:

'Form_Base
-------------------------------------------------------------
Public Class Form_Base

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

Protected Overridable Sub OnButtonClick()
MsgBox("From base")
End Sub

Protected Overridable Sub btn_OpenChild_Click(ByVal sender As
System.Object, ByVal e As System.EventArgs) Handles
btn_OpenChild.Click
Form_Child.Show()
End Sub
End Class
-------------------------------------------------------------

'Form_Child
-------------------------------------------------------------
Public Class Form_Child
Inherits Form_Base

Protected Overrides Sub OnButtonClick()
MsgBox("From child")
End Sub

Protected Overrides Sub btn_OpenChild_Click(ByVal sender As
Object, ByVal e As System.EventArgs)
Me.Close()
End Sub

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

Do you see anything that is wrong here, and could result in the double
event?

Thanks.

- Christian

Reply to this Message

Tom Shelton - 06 Mar 2008 20:57 GMT

> On 6 maalis, 22:34, Tom Shelton
><tom_shel...@YOUKNOWTHEDRILLcomcast.net> wrote:
[quoted text clipped - 159 lines]
> Me.Close()
> End Sub

---- Remvoe this -------------------------------------------------------

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

------------------------------------------------------------------------

> End Class
> -------------------------------------------------------------
>
> Do you see anything that is wrong here, and could result in the double
> event?

Remove the Button1_Click sub in the derived class. That is causing the
handler to be added twice. All you need to do is override the
OnButtonClick() method.

Signature

Tom Shelton

Reply to this Message

cride83@gmail.com - 06 Mar 2008 21:05 GMT

On 6 maalis, 22:57, Tom Shelton
<tom_shel...@YOUKNOWTHEDRILLcomcast.net> wrote:

> > On 6 maalis, 22:34, Tom Shelton
> ><tom_shel...@YOUKNOWTHEDRILLcomcast.net> wrote:
[quoted text clipped - 179 lines]
> --
> Tom Shelton

Yes!

That did the trick.
Now I know how to do similar things in the future. :)

Thank you so much.

- Christian.

Reply to this Message

Tom Shelton - 06 Mar 2008 21:10 GMT

> On 6 maalis, 22:57, Tom Shelton
><tom_shel...@YOUKNOWTHEDRILLcomcast.net> wrote:
[quoted text clipped - 191 lines]
>
> - Christian.

No problem....

Signature