Creating Activex DLL components

vbmo · #1 (**permalink**) June 5th, 2003, 04:59 AM

Hi there

I have been looking into find some pages with tutorials/artikles on creating DLL components but have not been able to find any. Can someone give me some links to that or give me an example on how to create Dll's ?

/vbmo

pgtips · #2 (**permalink**) June 5th, 2003, 09:43 AM

try these for "absolute beginner" articlers on using VB to create the DLLs:
http://www.4guysfromrolla.com/webtech/040300-1.shtml
http://www.microsoft.com/mind/0999/vbcom/vbcom.asp

vbmo · #3 (**permalink**) June 6th, 2003, 04:32 AM

Ok thanks But if there should be some tutorials/artikles on using Sql in the dll i would like those to :o)

/vbmo

pgtips · #4 (**permalink**) June 6th, 2003, 07:35 AM

How about these SQL and ADO tutorials?
http://www.w3schools.com/sql/default.asp
http://www.w3schools.com/ado/default.asp

any decent search engine will find you loads like these on the web...

Imar · #5 (**permalink**) June 6th, 2003, 02:55 PM

Hi vbmo,

What exactly are you looking for? If I recall correctly, Microsoft has created a sample application using a VB DLL for a common Data Access Layer with methods like ExecuteSprocGetRecordSet, ExecuteSQLetc. I searched google for this, but couldn't find it anymore.

The company I work for has used this example to create our own DAL, so if you have any specific questions, feel free to ask.

Cheers,

Imar

vbmo · #6 (**permalink**) June 6th, 2003, 05:45 PM

Hi Imar

I am simply looking for some toturials/artikles on creating dll's using VB. But the part with the "Hello World" is not enough i want to learn how to include sql and ado in my dll's :o)

/vbmo

Imar · #7 (**permalink**) June 7th, 2003, 08:17 AM

Hi vbmo,

I am sure there are a couple of tutorials / faqs on the net describing how to create a VB DLL using ADO, but I couldn't find one in my bookmarks. However, it's not too difficult. Using ADO in VB is more or less the same as in ASP. The biggest thing to watch for is passing parameters in and out of procedures. The type (strongly typed versus a Variant) of the parameters is important.

You can read more about that here: http://support.microsoft.com:80/supp...NoWebContent=1

OK, now for the "mini tutorial"

1. Start a new ActiveX DLL project and add a reference to the Microsoft ActiveX Data Objects 2.5/2.6

2. Create a property (type string) to hold the connection string. Alternatively, add the connection string as a hard coded value, although this is not recommended.

3. Add a method (a Sub) like ExecSproc with the following code:

Code:

Public Sub ExecSproc(ByVal NameOfSproc As String)
    '===============================================================
    '   NAME: ExecSproc
    '   DATE CREATED: 
    '   CREATED BY: 
    '   CREATED FOR: 
    '   FUNCTION: Executes a sproc that does not return any records
    '   IN: NameOfSproc. The name of the sproc to execute
    '   OUT: Nothing
    '   RETURNS: Nothing
    '   VERSION: 1
    '   EXAMPLE:
    '===============================================================

    On Error GoTo errorHandler

    Dim connConnection As ADODB.Connection
    Dim cmdCommand As ADODB.Command

    Set connConnection = New ADODB.Connection
    Set cmdCommand = New ADODB.Command

    With connConnection
        .Open YourConnectionString
    End With

    With cmdCommand
        ' Set command properties
        .ActiveConnection = connConnection
        .CommandType = adCmdStoredProc
        .CommandText = NameOfSproc
    End With

    ' Now execute without using a return value
    With cmdCommand
        .Execute , , adExecuteNoRecords
        .ActiveConnection = Nothing
    End With

    ' And clean up
    Set cmdCommand = Nothing
    Set connConnection = Nothing
    Exit Sub

errorHandler:
    If connConnection.State = adStateOpen Then
        connConnection.Close
    End If
    Set cmdCommand = Nothing
    Set connConnection = Nothing
End Sub

4. Compile the DLL and place it inside a COM+ package. See http://www.aspfree.com/authors/rober...ult.asp?aid=96 for more info on this.

5. Now you can use the DLL as follows in ASP:

Code:

Dim objDataAccess
Set objDataAccess = Server.CreateObject("MyProject.MyClassName")
objDataAccess.ExecSproc("sprocUpdatePrice")
Set objDataAccess = Nothing

As you can see, this is just a very short description of the situation. Of course you'll need more methods, properties etc to make this a successful Data Access component. Methods that you can implement are:

1. ExecSprocReturnRecordset - returns a strongly typed ADODB.Recordset
2. ExecSprocReturnArray - returns a Variant()
3. ExecSprocReturnInteger
4. ExecSQLReturnRecordset - accepts plain SQL instead of a sproc.

You'll also need a way to set up incoming parameters for the procedures.

All this code is based on the FMStocks sample site that Vertigo / Microsoft provided. If you go to http://www.fmstocks.com and download the FMStock 2000 sample project, you'll find all the stuff you need.

It looks like it's time I write a tutorial on how to create a DAL using the FMStock sample as a basis ;)

Cheers,

Imar

vbmo · #8 (**permalink**) June 10th, 2003, 02:56 AM

That was very usefull thanks a lot :o) Then i have just one question left, when i run a DLL under COM+ do i then not have to restart IIS when i compile my DLL again if there should be a bug in it ?

Imar · #9 (**permalink**) June 10th, 2003, 03:23 AM

Hi there,

You don't have to restart IIS ever when using COM+ (well, under normal circumstances that is. Sometimes it hangs and needs to be restarted anyway).

Even if you fix a bug all you need to do is follow the steps in the FAQ I posted.

You should also take some time to understand the GUID principle behind COM+ DLLs. If you don't make changes to the interface of your component (add / remove methods, add / remove parameters to existing methods etc) then the GUID for your component stays the same and your component is said to be binary compatible. If you do change the interface, a new GUID is assigned and your component might break (when used in other components / applications).

In both cases, you'll need to stop the package in COM+, remove the components from the package, replace the DLL and then add them again.

HtH

Imar

vbmo · #10 (**permalink**) June 10th, 2003, 08:27 AM

Ok thats nice to know thanks for your help :o)

And in the meantime i have found this one just if you want to read it, it is also a nice artikle : http://www.asp101.com/articles/carvi...ss/default.asp

Need to download code?

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