Custom Classes

[Keith Wilby]

I've been trying to get my head around custom classes by following the
example in the Visual Basic Language Developer's Handbook by Sybex. I think
I have a handle on what they're about, albeit a fragile one at the moment.
Having said that, I can't think of a single application for one so obviously
I need educating further. Does anyone have any practical examples of custom
classes and their application that might help me broaden my horizons?

Many thanks.

Keith.

[Gord]

Keith Wilby wrote:

"Rick Brandt" <ri*********@ho tmail.comwrote in message
news:JS******** ********@newssv r27.news.prodig y.net...

An easy example where *using* a class can be easier. Take my Email class.
As a class it works something like this.

Dim msg as New CDOMsg

With msg
.AddRecipient(" SomeAddress")
.Subject = "foo"
.TextBody = "bar"
.Send
End With

<snip>

Many thanks Rick. I think I'm OK using the class, it's what's in the class
itself that my small brain is struggling with. Here's what I have in my
Employee class so far:

Private mstrLastName As String
Private mstrFirstName As String
Private mdteDOB As Date
Private mintEmployeeNo As Integer

Property Get LastName()
LastName = mstrLastName
End Property

Property Get FirstName()
FirstName = mstrFirstName
End Property

Now it's the properties that are stumping me here because when I create a
new instance of Employee I want to assign values:

Dim objEmployee As clsEmployee
Set objEmployee = New clsEmployee
objEmployee.Las tName = "Wilby"
objEmployee.Fir stName = "Keith"

but of course this doesn't work. I'm not sure what's happening in those
property declarations.

The Property Get statements allow you to retrieve the value of the
named property. A Property Let statement will enable you to give the
property a value. I have never been a "classy" programmer , but I
believe the magic you seek is

Property Let LastName(ByVal vNewValue As Variant)
mstrLastName = vNewValue
End Property

(I'm sure that someone will correct me if I am wrong.)

[Keith Wilby]

"Gord" <gd*@kingston.n etwrote in message
news:11******** **************@ j44g2000cwa.goo glegroups.com.. .

>

The Property Get statements allow you to retrieve the value of the
named property. A Property Let statement will enable you to give the
property a value. I have never been a "classy" programmer , but I
believe the magic you seek is

Property Let LastName(ByVal vNewValue As Variant)
mstrLastName = vNewValue
End Property

(I'm sure that someone will correct me if I am wrong.)

Clearly I have much to learn still. Many thanks for that pointer Gord, I
will now go back to my book!

Regards,
Keith.

[jlepack]

Keith,

Your problem here is that oyu have followed sound programming
principles. You have created your variables within your class as
Private. Therefore, only methods and functions within your class can
access them, same as a private variable anywhere else for that matter.
As Gord correctly noted, these Get and Let methods can be accessed
publicly and therefore will allow non-local functions and procedures
that have an instance of your class to modify/view those values.

PS. You took the "unintersti ng path" and chose the employee and not
the slot machine ;)

Cheers,
Jason Lepack

Keith Wilby wrote:

"Rick Brandt" <ri*********@ho tmail.comwrote in message
news:JS******** ********@newssv r27.news.prodig y.net...

An easy example where *using* a class can be easier. Take my Email class.
As a class it works something like this.

Dim msg as New CDOMsg

With msg
.AddRecipient(" SomeAddress")
.Subject = "foo"
.TextBody = "bar"
.Send
End With

<snip>

Many thanks Rick. I think I'm OK using the class, it's what's in the class
itself that my small brain is struggling with. Here's what I have in my
Employee class so far:

Private mstrLastName As String
Private mstrFirstName As String
Private mdteDOB As Date
Private mintEmployeeNo As Integer

Property Get LastName()
LastName = mstrLastName
End Property

Property Get FirstName()
FirstName = mstrFirstName
End Property

Now it's the properties that are stumping me here because when I create a
new instance of Employee I want to assign values:

Dim objEmployee As clsEmployee
Set objEmployee = New clsEmployee
objEmployee.Las tName = "Wilby"
objEmployee.Fir stName = "Keith"

but of course this doesn't work. I'm not sure what's happening in those
property declarations. The logical part of my brain has quit for Christmas
already I think.

Keith.

[Rick Brandt]

Keith Wilby wrote:

"Gord" <gd*@kingston.n etwrote in message
news:11******** **************@ j44g2000cwa.goo glegroups.com.. .

>>

The Property Get statements allow you to retrieve the value of the
named property. A Property Let statement will enable you to give the
property a value. I have never been a "classy" programmer , but I
believe the magic you seek is

Property Let LastName(ByVal vNewValue As Variant)
mstrLastName = vNewValue
End Property

(I'm sure that someone will correct me if I am wrong.)

Clearly I have much to learn still. Many thanks for that pointer
Gord, I will now go back to my book!

Regards,
Keith.

The problem is you made those properties Private. Private properties are
either intended to be used strictly within the class or must have a Let (or
Set) function that can be used by code outside the class.

--
Rick Brandt, Microsoft Access MVP
Email (as appropriate) to...
RBrandt at Hunter dot com

[CDMAPoster]

Lyle Fairfield wrote:

Keith Wilby wrote:

I've been trying to get my head around custom classes by following the
example in the Visual Basic Language Developer's Handbook by Sybex. I think
I have a handle on what they're about, albeit a fragile one at the moment.
Having said that, I can't think of a single application for one so obviously
I need educating further. Does anyone have any practical examples of custom
classes and their application that might help me broaden my horizons?

There aren't a lot of uses for classes. The major one is to make
programers/developers feel that they have arrived.
I use my own classes almost never but over the years I have defended
them as useful for:
1. standardizing procedures in an application developed by many
persons; for example an append class;
2. allowing for multiple instances of code to exist concurrently; for
example code that persisted values while forms were closed and opened;
3. code which used objects or properties whose creation and or
initialization were time consuming; for example a numerals to words
procedure where arrays and strings were used.

You have used classes extensively if you have used forms that have
modules, and I expect that you have. The form module is, for all
extents [:-)] and purposes, a class module. It has initalization and
termination procedures (form_open and form_close), properties in the
form of controls or property definitions, and can have multiple
instances. IMO the form is a very superior Class. When invisible it
acts just like a class. It can be made visible on demand (and invisible
again on demand) to get input from the user, to show as progress bar,
to show a message, etc and as a single default entity it does not have
to be initialized; we can jst call Form_MYClass.Do Something()
[DoSomething is a Public Procedure] and slam, bam it's done.

Slam, bam, thank-you RAM? Is that from a call to
Form_ClassicRoc k.GetAlteredLyr icSnippet()?

James A. Fortune
CD********@Fort uneJames.com

[Albert D. Kallal]

I give some thoughts and helpfull advice here:
Using Class objects with ms-access.
By Albert D. Kallal
Tuesday, September 16, 2003

Why would I want to use a class object in ms-access?

http://www.members.shaw.ca/AlbertKal.../WhyClass.html
--
Albert D. Kallal (Access MVP)
Edmonton, Alberta Canada
pl************* ****@msn.com

[Keith Wilby]

"Albert D. Kallal" <Pl************ *******@msn.com wrote in message
news:GkHbh.3984 09$5R2.297739@p d7urf3no...

>I give some thoughts and helpfull advice here:
Using Class objects with ms-access.
By Albert D. Kallal
Tuesday, September 16, 2003

Why would I want to use a class object in ms-access?

http://www.members.shaw.ca/AlbertKal.../WhyClass.html

Thank you Albert, I will read that now.

[Keith Wilby]

"jlepack" <jl*****@gmail. comwrote in message
news:11******** **************@ l39g2000cwd.goo glegroups.com.. .

Keith,

Your problem here is that oyu have followed sound programming
principles. You have created your variables within your class as
Private. Therefore, only methods and functions within your class can
access them, same as a private variable anywhere else for that matter.
As Gord correctly noted, these Get and Let methods can be accessed
publicly and therefore will allow non-local functions and procedures
that have an instance of your class to modify/view those values.

Duly noted, thanks.

>
PS. You took the "unintersti ng path" and chose the employee and not
the slot machine ;)

That's the kinda guy I am ;)

>
Cheers,
Jason Lepack

[Keith Wilby]

"Albert D. Kallal" <Pl************ *******@msn.com wrote in message
news:GkHbh.3984 09$5R2.297739@p d7urf3no...

>I give some thoughts and helpfull advice here:
Using Class objects with ms-access.
By Albert D. Kallal
Tuesday, September 16, 2003

Why would I want to use a class object in ms-access?

http://www.members.shaw.ca/AlbertKal.../WhyClass.html

Just a quick question Albert.

"when I create and set the myTour = "tour id", then all of the recordsets
for bus company, hotels, rates etc gets loaded into the object."

Could you just expand a little on this please? How does the data get
loaded, do you open a recordset in a subroutine? Still missing the point
here I think!

Thanks.

Keith.

[Gord]

Keith Wilby wrote:

"Albert D. Kallal" <Pl************ *******@msn.com wrote in message
news:GkHbh.3984 09$5R2.297739@p d7urf3no...

I give some thoughts and helpfull advice here:
Using Class objects with ms-access.
By Albert D. Kallal
Tuesday, September 16, 2003

Why would I want to use a class object in ms-access?

http://www.members.shaw.ca/AlbertKal.../WhyClass.html

Just a quick question Albert.

"when I create and set the myTour = "tour id", then all of the recordsets
for bus company, hotels, rates etc gets loaded into the object."

Could you just expand a little on this please? How does the data get
loaded, do you open a recordset in a subroutine? Still missing the point
here I think!

Thanks.

Keith.

Hi, Keith.

Here is a simple example of what I *think* Albert is driving at. Notice
that the "Property Let "Salary_Gra de" not only saves the Salary_Grade
you pass it, as in...

objEmployee.Sal ary_Grade = 3

....but it also looks up the corresponding Annual_Salary and saves that
as well, so you can retrieve it via...

objEmployee.Ann ual_Salary

....without doing the lookup yourself.
'-----class module code follows-----

Option Compare Database
Option Explicit

Private mstrLastName As String
Private mintSalary_Grad e As Integer
Private mcurAnnual_Sala ry As Currency

Public Property Get LastName()
' return property value
LastName = mstrLastName
End Property

Public Property Let LastName(ByVal vNewValue As Variant)
' store property value
mstrLastName = vNewValue
End Property

Public Property Get Salary_Grade() As Variant
' return property value
Salary_Grade = mintSalary_Grad e
End Property

Public Property Let Salary_Grade(By Val vNewValue As Variant)
' store property value...
mintSalary_Grad e = vNewValue
' ... and look up annual salary from reference table
mcurAnnual_Sala ry = _
DLookup("Annual _Salary", "Salaries", "Salary_Gra de=" &
mintSalary_Grad e)
End Property

Public Property Get Annual_Salary() As Variant
' return property value
Annual_Salary = mcurAnnual_Sala ry
End Property