Go Premium for a chance to win a PS4. Enter to Win

x
?
Solved

How to find whether object exists?

Posted on 2001-06-17
6
Medium Priority
?
196 Views
Last Modified: 2012-05-04
Consider a situation that I have an ADO connection objet named cn. Now I have closed the object as :

cn.close

and have released the resources as :

Set cn = Nothing.

Now if I call some routine that uses the ADO cn object and refer to it program would give me an error. I want that my program must first confirm whether this object exists then refer to it. HGow can I do this.
0
Comment
Question by:ShehzadMunir
6 Comments
 
LVL 6

Accepted Solution

by:
sharmon earned 30 total points
ID: 6199634
Dim cn As ADODB.Connection

Private Sub Form_Load()

  Set cn = New ADODB.Connection
  'Setup and open, etc...

  If cn.State = adStateOpen Then cn.Close
  Set cn = Nothing

  Dim fResult As Boolean
  fResult = cn Is Nothing
  Debug.Print fResult
End Sub
0
 

Expert Comment

by:ostrosoft
ID: 6199659
...
On Error Resume Next
If cn.State = adStateClosed Then MsgBox "Connection closed"
If Err <> 0 Then MsgBox "Object destroyed"
On Error GoTo 0
...
0
 
LVL 3

Expert Comment

by:RodStephens
ID: 6199663
If cn Is Nothing Then
    ' Connection doesn't exist...
Else
    ' Connection exists...
End If

To see if the connection is open, use:

    If cn.State = adStateOpen Then ...
0
Concerto's Cloud Advisory Services

Want to avoid the missteps to gaining all the benefits of the cloud? Learn more about the different assessment options from our Cloud Advisory team.

 
LVL 6

Expert Comment

by:sharmon
ID: 6199693
ostrosoft, closing a connection doesn't destroy the object.

RodStephens, your code is basically the same as mine...
0
 
LVL 3

Expert Comment

by:Hornet241
ID: 6200155
Checking the cn.state after Set cn = Nothing will cause an error Try this code

Function ChkValidConnection()
On Error GoTo ErrorHandler:

'Just to Check
Set conn = Nothing

Chkconn = IsObject(conn)
If Chkconn = True Then
    If conn.State = 1 Then
      conn.Close
    End If
  Else
    'use this if necessary
    Dim conn As ADODB.Connection
    Set conn = New ADODB.Connection
End If

conn.Open "ConnectionString"

ErrorHandlerExit:
  Exit Function

ErrorHandler:
  If Err = 91 Then  ''Object variable not set
      Set conn = New ADODB.Connection
      Resume
    Else
      MsgBox "Unhandled Error"
      Resume ErrorHandlerExit:
  End If

End Function
0
 

Author Comment

by:ShehzadMunir
ID: 6200946
Because object cannot be referred after being destroyed.

Actually right now I am not seeing any Accept Answer button. Though I have accepted sharmon 's answer in a sense that we can check the connection existance by keeping a boolean variable. : Hornet241 is absolutely right. But since Sharmon attempted first so no he would be awarded the marks.

Thanks for all who answered.
0

Featured Post

Free Tool: IP Lookup

Get more info about an IP address or domain name, such as organization, abuse contacts and geolocation.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Background What I'm presenting in this article is the result of 2 conditions in my work area: We have a SQL Server production environment but no development or test environment; andWe have an MS Access front end using tables in SQL Server but we a…
This article describes some techniques which will make your VBA or Visual Basic Classic code easier to understand and maintain, whether by you, your replacement, or another Experts-Exchange expert.
As developers, we are not limited to the functions provided by the VBA language. In addition, we can call the functions that are part of the Windows operating system. These functions are part of the Windows API (Application Programming Interface). U…
Show developers how to use a criteria form to limit the data that appears on an Access report. It is a common requirement that users can specify the criteria for a report at runtime. The easiest way to accomplish this is using a criteria form that a…
Suggested Courses

926 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question