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Tip of the Day
Language: Visual Basic
Expertise: Intermediate
Nov 5, 1999

WEBINAR:

On-Demand

Application Security Testing: An Integral Part of DevOps


Share Variables Between Multiple Apps

Sometimes it's necessary to share variables between multiple instances of an application. For example, you might want to share a database connection. Here's how: Create an ActiveX EXE with an exposed MultiUse class named Class1. An ActiveX DLL won't work because it's running in-process within each client. Include a module in the project and declare the required variable you want to share in this module as a public variable.

The code in an ActiveX DLL looks like this:

 
'**** Module code *****
Global gCon As Database
Global glngNrOfObjects As Long

'**** Code in Class ****
Public Property Set DBConn(Con As Database)
	Set gCon = Con
End Property
Public Property Get DBConn() As Database
	Set DBConn = gCon
End Property

Private Sub Class_Initialize()
	' this variable keeps count of objects created
	glngNrOfObjects = glngNrOfObjects + 1
End Sub
Private Sub Class_Terminate()
	' decrease object count
	glngNrOfObjects = glngNrOfObjects - 1

	' if no objects exist, close the connection
	If glngNrOfObjects = 0 Then
		If Not gCon Is Nothing Then
			gCon.Close
			Set gCon = Nothing
		End If
	End If
End Sub
Now reference this ActiveX EXE in your project and use it. Here's how I did it:
 
'** Code in application using the ActiveX EXE **

Dim clsDBConn As Class1

Private Sub Form_Load()
	Set clsDBConn = New Class1
	' set the connection, when first object is 
	' created
	If clsDBConn.DBConn Is Nothing Then
		Set clsDBConn.DBConn = _
			Workspaces(0).OpenDatabase( _
			"\temp\db1.mdb")
		End If
End Sub

Private Sub Form_Unload(Cancel As Integer)
	Set clsDBConn = Nothing
End Sub
You don't need to include the code to count the object instances and close the database if your variable is a simple one-that is, if it's not an object reference. Also, in that case, change the Property Set to Property Let.

Both the projects have a reference to DAO because they're using the database object.

Ravindra Okade
 
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