class structures

**stanigator** · 11-14-2007, 06:19 PM

I am not too familiar with working with visual basic class objects (but worked with C++ class objects before). I'm trying to modify another developer's code separately, so I am trying to incorporate a minimal class definition required to help myself with the development. Given the following subroutine:

Sub ifctStage_class_test()

On Error GoTo localErr          ' Error Handling

Dim filepath As String          ' for file manipulation
Dim testStages() As ifctStage

Set testStages(0) = New ifctStage

Exit Sub

localErr:       'only operates correctly if user is operating on Angstrom network with smtp server setup
    MsgBox "error occurred"
    Exit Sub
End Sub

with the following class declaration:

'Angstrom Power
'Data Analysis Tool v0.1
'Programmer: Bruno Bate, Stanley Lee
'Created: 08/03/07 [mm/dd/yyyy]
'Last Modified: 14/11/07

'Overview: class pertaining to each stage of an AFCT test.  An instance of the class is called
'whenever a new stage is encountered.
Option Explicit

Private rawStageData(5, 1000000) As Double      'array holding .csv file data

'variables for info stored in headers
Dim UUT As String               ' Fuel Cell Identifier
Dim teststation As Integer      ' test station identifier
Dim mode As String              ' test mode
Dim setPoint As Double          ' current set-point
Dim sampleT As Long             ' Sampling period
Dim startTime As String         ' Start Date and Time
Dim comment As String           ' comments
Dim numSamples As Long          ' number of samples


'placeholder variables for columns.Referencing these will clean code and simplify reading
Private xStage As Long          'Stage column placeholder
Private xTime As Long           'time column placeholder
Private xVoltage As Long        'voltage column placeholder
Private xCurrent As Long        'current column placeholder
Private xT1 As Long             'T1 temperature column placeholder
Private xT2_Mflow As Long       'T2/Mass Flow colum placeholder
Private xPower As Long          'power column placeholder

'Subroutine executed when new instance of class created
Private Sub Class_Initialize()
   'initialize public class variables
   UUT = "blank"
   teststation = 0
   sampleT = 0
   mode = "blank"
   setPoint = 0
   startTime = "blank"
   xStage = 0
   xTime = 1
   xVoltage = 2
   xCurrent = 3
   xT1 = 4
   xT2_Mflow = 5
   xPower = 6
   
End Sub

Is there something missing in the class definition in order to have my subroutine working?

**Leith Ross** · 11-14-2007, 06:32 PM

Hello stanigator,

A class has to be placed into a VBA Class Module. The name of this module is what VBA will refer to when you instantiate the Class using a Dim statement. So far, your class has only private data. Data that is hidden from the user that is used internally for the Class structure. To allow the user to interact with the Class you must create public properties, by using the Property Get, and Property Set statements along with methods. Methods are public Sub and/or Functions procedures design to manipulate Class information. A Class in VBA is not really the same as in C or C++. VBA Class objects don't inherit other objects properties and methods. Also they only support a single instance of creation.

Sincerely,
Leith Ross

**stanigator** · 11-14-2007, 06:46 PM

For the class, I did indeed put it inside a VBA class module. I have looked up Property Get and Property Set statement descriptions on MSDN, but still quite unsure of how to use them to get my classes working. Do you happen to have an example? Would be much appreciated.

**Leith Ross** · 11-14-2007, 08:16 PM

Hello Stanigator,

I can code something up this evening, and post it for you. I have to attend to some other business shortly, and won't be able to do anything until later this evening.

Sincerely,
Leith Ross

**lecxe** · 11-15-2007, 01:13 AM

Hi stanigator

To get you started:

Your error is in the standard module. You are not allocating space to the array.

Dim testStages() As ifctStage

declares an array with no space allocated. You have to use ReDim to size the array. For example, in the standard module:

...
Dim testStages() As ifctStage

ReDim testStages(0 To 4)

Set testStages(0) = New ifctStage

MsgBox testStages(0).xtimeP

Exit Sub
...

The ReDim statement allocates space to 5 objects.

I display the value of the property xtimeP, that reflects the value of the object's private variable xtime. To get it, add at the end of your ifctStage class module:

Property Get xtimeP() As Long
xtimeP = xtime
End Property

HTH
lecxe

**Leith Ross** · 11-15-2007, 12:59 PM

Hello stanigator,

Here is simple class. Hopefully this will clearly illustrate the basic components, and structure of a class module.

Add a Class Module to project and rename it StopWatchCls. The class contains 4 properties: EventID, Hours, Minutes, Seconds. EventID is a read/write property, while the others are read only. There are 3 methods: StartWatch, StopWatch, and Elapsed. Only Elapsed returns a value. It returns the elapsed time as string formatted in "HH:MM:SS".

Class Module Code

'Stop Watch Class -
'  Properties: Hours, Minutes, and Seconds
'  Methods: Start, Stop, and Elapsed

'-----------------------------------------'
' Declare Private Variables for Class use '
'-----------------------------------------'

  Dim Hrs As Long
  Dim Mins As Long
  Dim Secs As Long
  Dim StartTime As Double
  Dim StopTime As Double
  Dim ET As Double
  Dim pvtEventID As String

'-------------------------------'
' Public Properties - Read Only '
'-------------------------------'

  Public Property Get Hours() As Long
    Hours = Hrs
  End Property
    
  Public Property Get Minutes() As Long
    Minutes = Mins
  End Property

  Public Property Get Seconds() As Long
    Seconds = Secs
  End Property
  
'-------------------------------'
'  Public Property - Read/Write '
'-------------------------------'

  Public Property Get EventID() As String
    EventID = pvtEventID
  End Property
   
  Public Property Let EventID(Event_ID As String)
    pvtEventID = Event_ID
  End Property
   
'----------------'
' Public Methods '
'----------------'

  Public Sub StartWatch()
    StartTime = Now()
      Hrs = 0
      Mins = 0
      Secs = 0
  End Sub

  Public Sub StopWatch()
    StopTime = Now()
  End Sub
  
  Public Function Elapsed() As String
    ET = StopTime - StartTime
    Elapsed = Format(ET, "hh:mm:ss")
      ET = ET / (1 / 86400)     'Elapsed time is stored in seconds
      Hrs = Int(ET / 3600)
      Mins = Int(ET / 60)
      Secs = ET Mod 60
  End Function

StopWatch Example
Place this code in a Standard VBA module

Sub StopWatchTest()

  Dim I As Long, J As Long
  Dim H As Long, M As Long, S As Long
  Dim ID As String
  Dim MyStopWatch As New StopWatchCls
  Dim X As String
  
    MyStopWatch.StartWatch
      For I = 1 To 5000
        For J = 1 To 256
          n = n + Val(Cells(I, J))
        Next J
      Next I
    MyStopWatch.StopWatch
    
    With MyStopWatch
      .EventID = "Time Test 1"
      X = .Elapsed
      H = .Hours
      M = .Minutes
      S = .Seconds
      ID = .EventID
    End With
    
End Sub

Sincerely,
Leith Ross

class structures

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