[RESOLVED] Variable Automation by Reference?

[Jim Davis]

Hey! Long time no posting here So here i go.

Im just want to pass a variables reference to a class, then im want to change the referenced variables value later, outside the subroutine there i passed the variable to.

Here is my idea, im seeking for any workaround.

'In a module:
Global myVarAutomated as long

'In a form:
Private clsObj as myClassObj

Private Sub Form_Load()
  Set clsObj = new myClassObj
  clsObj.Init myVarAutomated 'passing the reference

  clsObj.IncValue 10 'Increase the value by 10

  msgBox myVarAutomated 'Now at this point im want to display the value of the variable that increased before. :)

End Sub

The problem is in the class.

Private AutomatedValue 'as any, or what?

Sub Init(ByRef aVal)
  Set AutomatedValue = aVal
End Sub

Sub IncValue(ByVal lVar as long)
  AutomatedValue = AutomatedValue + lVar
End Sub

No it isnt works.. but how can i get it to work?
Thanks
J

[RhinoBull]

Not sure I completely understand however it sounds like you want to pass class id (or prog id) to your class and from that class create object.
If so then look at the following sample:

'this goes to your form
Option Explicit

Private Sub Command1_Click()
'============================
Dim myObj As Object
Dim myProgID As String
Dim myClass As clsAutomation

    myProgID = "Word.Application"
    Set myClass = New clsAutomation
    
    Set myObj = myClass.CreateMyObject(myProgID)
    myObj.Visible = True
    

End Sub

'class module:
Option Explicit

Public Function CreateMyObject(strProgID As String) As Object
Dim obj As Object

On Error GoTo ErrHandler

    Set obj = CreateObject(strProgID)
    
    Select Case strProgID
        Case "Word.Application"
            'perhaps you need to open some template...
        Case "Excel.Application"
            'do whatever...
    End Select
    
    Set CreateMyObject = obj
    Set obj = Nothing
    
    Exit Function

ErrHandler:

    MsgBox Err.Description
    Err.Clear
    Exit Function

End Function

You may expand/change sample code as you wish.

[Jim Davis]

Lol no its completely different

So basically im want to pass a reference of a variable to the class, then im want to modify the value of the variable in an another sub.

I think the only way this could work, if i store the reference id of the variable, or just bind an another variable to the referenced variable. So this way when i change the value of the variable in the class, that will set the value of the original variable also...

but how can i do it?

[RhinoBull]

If variable is passed ByRef (which is default in VB6) then you can change its original value:

'in nthe form:
Private Sub Command1_Click()
'============================
Dim myValue As String
Dim myClass As Class1

    myValue = "abc"
    Set myClass = New Class1
    
    Debug.Print "myValue used to be " & Chr(34) & myValue & Chr(34)
    myClass.Test myValue
    Debug.Print "and now it is " & Chr(34) & myValue & Chr(34)

End Sub

'in the class
Public Function Test(ByRef a As String) As String
    Test = a & "123"
    a = "hello from class"
End Function

If you want to preserve original value then you need to pass variable ByVal.

[Jim Davis]

Yeah i know, but what if im want to change the value in a different sub (in class ) that couldnt get the reference of the variable? So is there any way to STORE the reference id, then modify the referenced variable later?..

eg:
'in module
Global myVar as Long

'in a form sub
myClass.Init myVar 'pass the reference
myClass.Set 10 'it modifies myVar.

Please recheck my first post, that might be helpful to understand my problem..

[Jim Davis]

.. or just how can i get the memory pointer of the variable, then how can i write there to modify its value..

[RhinoBull]

Visual Basic was not designed to support pointers.
However, to fill this hole MS decided to do something in VB5/6 just to bring down the noise I guess.
Have a look at this KB article: How To Get the Address of Variables in Visual Basic

[Jim Davis]

Aww sweet, varptr and strptr are exactly im looking for.

ive just played a bit with this copymemory API and it wors fine. Ive just did two little examples, that shows how is it works. So this way i can store the reference (memory pointer) of a string variable then i can modify its value from wherever and whenever i want.

However ive tried to build it into my app, then ive got some strange results. Sometimes it crashes the app, but sometimes give me wrong results... and it works only on a few times

Im not sure why. Do you have any ideas? Is this the answer? -> http://vbforums.com/showpost.php?p=2745456&postcount=2

Anyway.. Thanks for pointing me to the right direction.
J