Simple AcitveX DLL QUESTION (I hope)

In this code:

Code:

---

Option Explicit

' PROPERTIES':
Private m_comm As MSComm
Private m_num As Long
Private m_str As String

' METHODS:
Public Sub function1()
    m_str = "Str1"
    m_num = 1
End Sub

Public Sub function2(ByVal var As String)
    m_str = "Str2"
    m_num = 2
    m_comm.CommPort = 1                  <-------!!!! ERROR!!!!!
End Sub

---

Error: "Object variable or With block variable not set (Error 91)"


Why I can't assign the value ?????

Thanks

m_comm is an object and must be assigned to something before it can be used. Somewhere in your class you need to assign an instance of the MSComm control to your m_comm variable.

Typically a property Get/Set is used

VB Code:

Public Property Get Communications() as MSCommLib.MSComm 
   Set Communications = m_comm
End Property
 
Public Property Set Communications(CommControl as MSCommLib.MSComm 
   Set m_comm = CommControl
End Property
 
Private Sub Class_Terminate()
    Set m_comm = nothing
End Sub

Thank you brucevde for the answer.

But I don't understood this:

GET/SET Properties are used to communicate with the class; they are used to READ a private member variable and to WRITE a private member varable from outside the class (i.e: from the exe application that "call" the class).

But in my case I'm WRITING the private member variable from within the class => I don't understand the error.


I hope u'll reply me.

MatteoXMad

MSComm is a control and must be put on a form same as a textbox, label etc.. You cannot create a new instance of the MSComm control within your class - you need a form. This means you need some method of telling your class which control you want it to use, thus the Property Get/Set.

This is no different than your exe application calling your class. Let's say your class is named clsCommPort and you code these lines.

Dim objCommPort as clsCommPort
objCommPort.Function1

You will receive the error 91 in your exe because you have not created an instance of the class object. You must add the line Set objCommPort = New clsCommPort.

After your answer I tried many solutions, without a correct result.

PROJECT ActiveX DLL named Class1:

VB Code:

Option Explicit
 
' PROPERTIES':
Private m_comm As MSComm
Private m_num As Long
Private m_str As String
 
Public Sub function1(ByVal var As String)
    MsgBox var
    m_str = "Str1"
    m_num = 1
    m_comm.CommPort = 1                   '<-------!!!! ERROR!!!!!
End Sub
 
Public Property Get Communications() As MSCommLib.MSComm
   Set Communications = m_comm
End Property
 
Public Property Set Communications(CommControl As MSCommLib.MSComm)
   Set m_comm = CommControl
End Property

PROJECT Standard EXE (that call Class1):

VB Code:

Private Sub Command1_Click()
    Dim class As New Class1
    class.function1 ("pippo")
End Sub

An error occur immediatly with GET/SET Properties...

:-(
Help me!

MatteoXMad

Since you are creating a DLL you are probably getting the error "Private objects cannot be used in Public..." , the rules are different for ActiveX DLLs. You need to declare your Property Get/Set as the generic Object and then test to make sure the client is passing a control of the correct type.

PROJECT ActiveX DLL named Class1:
-- Note that this project must reference the Microsoft MSComm Control component.

VB Code:

Option Explicit
 
' PROPERTIES':
Private m_comm As MSComm
Private m_num As Long
Private m_str As String
 
Public Sub function1(ByVal var As String)
    MsgBox var
    m_str = "Str1"
    m_num = 1
    m_comm.CommPort = 1   
End Sub
 
Public Property Get Communications() As Object  '<---Changed to As Object
   Set Communications = m_comm
End Property
 
Public Property Set Communications(CommControl As Object) '<---Changed to As Object
   If Typeof CommControl Is MSCommLib.MSComm Then '<---Check if the class is passed the proper cotnrol
        Set m_comm = CommControl 
   Else
         Err.Raise -1,,"Requires a Microsoft Comm Control" '<--Raise an error to the client app
   End if
End Property

PROJECT Standard EXE (that call Class1): - You still have not told the Class which instance of the Comm control it should use.

VB Code:

Private Sub Command1_Click()
    Dim class As New Class1
    Set class.Communications = Form1.MSComm1 '<--- Tell the class to use the Comm control on Form1.
    class.function1 ("pippo")
End Sub

Thank u very much for your replies. I'll try as soon as possible.

MatteoXMad

Code:

---

Thank you very much for your help, the code you gave me works.

You are GREAT, really!

So this is the CONCLUSION:

If an EXE Application wants to call the function connect() of the ActiveX DLL and this function use some components
(i.e. MSComm)  =>  also the EXE App. MUST reference those components!!!

 
                        ------------------
  ------------ connect() |                |
  |          |---------->|  ActiveX DLL  |
  | EXE App. |          |                |
  |          |<----------|  MSComm      |
  ------------          |    |          |
                        ------|-----------
                              |
                              |----> serial line


There's no way to do this without using references in the EXE App.????


Thanks again


MatteoXMad

---

Never say never. I probably should have mentioned this before but there is a way to have the ActiveX DLL handle everything. This hides the fact that you are using the MSComm control from the EXE application. You could easily upgrade the DLL with a different control in the future without affecting the EXE.

Add a Form to your DLL project that contains an MSComm control, my example below names it frmCommunications.
When a new instance of your Class is created load an instance of the form (it doesn't have to be visible).
Your class could use its instance of the form to call the control directly.
The Get/Set properties in the first example can be removed from the class.

You might have problems if two programs are using the DLL at the same time.

VB Code:

'Private m_comm As MSComm '<---No longer required
Private m_num As Long
Private m_str As String
Private frmMyComm as frmCommunications
 
Public Sub function1(ByVal var As String)
    MsgBox var
    m_str = "Str1"
    m_num = 1
    frmMyComm.MSComm1.CommPort = 1  '<--Call the control directly
End Sub
 
Private Sub Class_Initialize
   Set frmMyComm = New frmCommunications  '<--initialize the class instance of the form
   Load frmMyComm
End Sub
 
Private Sub Class_Terminate
   Unload frmMyComm '<-- make sure everything is cleaned up
   Set frmMyComm = Nothing
End Sub

Standard EXE (that call Class1) does not need to reference the MSComm control and can simply be called by this function (hey that's what you had originally).

VB Code:

Private Sub Command1_Click()
    Dim class As New Class1
    class.function1 ("pippo")
End Sub

Hope this gives you more ideas.

Thank u again for the answer. I'll try to use the code u give me as soon as possible. It looks like that it'll work.

So we've understood that to use objects inside a class, we must include these in a form.

Do u know c++? It works different, really?

Bye

Mad

Quote:

---

So we've understood that to use objects inside a class we must include these in a form

---

That should be "to use controls inside a class we must include these in a form." Any COM object can be used in a class.

I am familiar with C++ but my career took me down the VB path. I would have trouble writing any windows program in C nowadays. Its been so long (6+ years).

Why? Objects or controls are so different?
Maybe, when we speak about controls, we are referring to ActiveX and COM architecture?

Bye