Cancelling an event

[LeonX]

Hi guys,

I need some help from you, I wonder how can I make a class with events like MDIForm_QueryUnload(Cancel as Integer, UnloadMode as Integer)? When I set Cancel to non zero value it can abort the unload method.

Thanks in advance.

[LeonX]

I have tried something like this in my class module.

Private mPrevValue As Integer
Private mCurrValue As Integer
 
Public Event ValueChanged(PrevValue As Integer, NewValue As Integer, Cancel As Boolean)
 
Public Property Get Value() As Integer
Value = mCurrValue
End Property
 
Public Property Let Value(byval NewValue As Integer)
Dim Cancel As Boolean
Cancel = False
RaiseEvent ValueChanged(mPrevValue, NewValue, Cancel)
If (Not Cancel) then
mPrevValue = mCurrValue
mCurrValue = NewValue
End If
End Property

And the following in my project.

Dim WithEvents c As MyClass.Test
 
Private Sub c_ValueChanged(PrevValue As Integer, NewValue As Integer, Cancel As Boolean)
If (NewValue > 10) Then
Cancel = True
End If
End Sub
 
Private Sub Form_Load()
Set c = CreateObjects("MyClass.Test")
c.Value = 1
c.Value = 5
c.Value = 13
MsgBox c.Value
End Sub

Why the value still 13? I want to Cancel the value from changing if the new value greater than 10. What should I do to get this?

Thanks in advance.

[dRAMmer]

You do neet and event if that is all you are trying to do. WHat you may want for you event rather is to be able to raise a message.

Public Property Let Value(byval NewValue As Integer)
If NewValue < = 10 Then 
   mCurrValue = NewValue
Else 
   'do nothing with your private variable representing the property, in this manner you retain the current value 
   'and you might want to have something like
   MyPrivateErrorNo = 101 'you may have your own numbering 
   err.raise MyPrivateErrorNo , , "Invalid value."
End If
End Property
 
And in your project.
 
Dim WithEvents c As MyClass.Test
Private TestSub ()
   On Error Goto err_handler
   c.value = 20
  on error goto 0
  Exit sub
err_handler:
   if err.number<>0 then msgbox err.description
  on error goto 0
End Sub

[LeonX]

Yes, I can do it that way, but it has a fixed validation rule, and everytime the rule change I must change my code.

And furthermore its just a sample of condition, the point is I want to rollback the value, if it is not satisfied the condition given.

Anyway thanks dRAMmer.
Have any ideas to help me?

[LeonX]

Hello ...
I really need this help, can anyone help me?

[brucevde]

Why the value still 13? I want to Cancel the value from changing if the new value greater than 10. What should I do to get this?

I ran some tests and there is nothing wrong with the code you posted. It works as expected. However, I only tested within the IDE.

Is the s on the end of CreateObjects just a typo, or is that your own procedure? If your own procedure can you post the code.

One recommendation. Change the declaration of the Event procedure to pass the Value variables ByVal (this has nothing to do with your problem). Otherwise, the value can be changed without using the Property Let procedure.

Public Event ValueChanged(ByVal PrevValue As Integer, ByVal NewValue As Integer, Cancel As Boolean)

[LeonX]

Upss, sorry the "s" its a mistyping. And I'm embrassed to say that the code its working now, maybe I just mistyping the code before.
But thanks to you brucevde, I will change the declaration of the parameter with ByVal.
Thanks bruce.

[pnish]

If you put Option Explicit in the general declarations section of each form & module etc you won't have these sort of problems. This will cause the compiler to pick up any spelling errors or undefined varaibles.

You can also get VB to do this for you automatically. Go to the Tools menu and select Options, go to the Editor tab and check the box labelled Require Variable Declaration