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.

[jlepack]

Re: Custom Classes

Anything can be a custom class. Think of anything that has multiple
variables and you can make it into a custom class.

Take an Employee for example. I am an employee, you presumably are an
employee.

At the root, all employees have a first name, last name, birthdate,
SSN, etc. You could store each of those variables and have a
JasonLepack as Employee, or a KeithWilby as Employee.

Another example is a slot machine. Each slot machine has a few
variables.
It has a cost structure, payout structure, amount of money in it, data
on the reels, current position of reels.

On top of that a slot machine has actions (functions) that can be
performed. You could depositMoney, pullArm, fullPlay (the button on
the front), payOut.

Hope that makes a little more sense.

Cheers,
Jason Lepack

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?
>
Many thanks.
>
Keith.

[Rick Brandt]

Re: Custom Classes

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?
Many thanks.
>
Keith.

I have classes that ...

Provides the Windows File Browser dialog
Creates and sends an Email using Outlook
Creates and send an Email using CDO
Displays a custom Message Dialog Form
(others that are to esoteric to bother describing)

There are times when having a bunch of related code in a class is better
than just having functions and sub-routines in a module. Classes can expose
certain things while not exposing others. You can instantiate multiple
objects of a Class at the same time. Since they are instantiated as objects
you can pass them around between other functions and sub-routines.

I'm not an expert at using them in Access and Classes in VBA have some
limitations, but they definitely have their place. Some developers uses
classes more than others especially if they came from a programming
background where object-oriented was stressed.

It is good to learn about Classes and be able to dig into those you
encounter and see what's going on, but don't feel guilty if you can't think
of hundreds of ways to use them. In most cases plain old functions and
sub-routines solve the problem in the best fashion.

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

[Lyle Fairfield]

Re: Custom Classes


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.

[Keith Wilby]

Re: Custom Classes

"Rick Brandt" <rickbrandt2@ho tmail.comwrote in message
news:swBbh.1407 $Py2.754@newssv r27.news.prodig y.net...

>
It is good to learn about Classes and be able to dig into those you
encounter and see what's going on, but don't feel guilty if you can't
think of hundreds of ways to use them. In most cases plain old functions
and sub-routines solve the problem in the best fashion.
>

You've hit the nail right on the head there Rick because I do extensively
use subs/functions to return values and perform various tasks, I suppose I'm
going to have to keep reading up until the penny fully drops to see if any
would be more efficient as a class. Thanks for your response.

Keith.

[Keith Wilby]

Re: Custom Classes

"jlepack" <jlepack@gmail. comwrote in message
news:1164895226 .867182.261250@ 80g2000cwy.goog legroups.com...

Anything can be a custom class. Think of anything that has multiple
variables and you can make it into a custom class.
>
Take an Employee for example. I am an employee, you presumably are an
employee.
>
At the root, all employees have a first name, last name, birthdate,
SSN, etc. You could store each of those variables and have a
JasonLepack as Employee, or a KeithWilby as Employee.
>

<snip>

Thanks Jason, I'll have a go at creating one of those, should help that
penny drop.

Regards,
Keith.

[Keith Wilby]

Re: Custom Classes

"Lyle Fairfield" <lylefairfield@ aim.comwrote in message
news:1164896452 .192808.311430@ j72g2000cwa.goo glegroups.com.. .
<snip>

Thanks Lyle.

[Rick Brandt]

Re: Custom Classes

Keith Wilby wrote:

"jlepack" <jlepack@gmail. comwrote in message
news:1164895226 .867182.261250@ 80g2000cwy.goog legroups.com...

>Anything can be a custom class. Think of anything that has multiple
>variables and you can make it into a custom class.
>>
>Take an Employee for example. I am an employee, you presumably are
>an employee.
>>
>At the root, all employees have a first name, last name, birthdate,
>SSN, etc. You could store each of those variables and have a
>JasonLepack as Employee, or a KeithWilby as Employee.
>>

<snip>
>
Thanks Jason, I'll have a go at creating one of those, should help
that penny drop.
>
Regards,
Keith.

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

Now, that class has lots of other properties and methods that I might use
from time to time, but most often I only use the ones you see above. If I
wrote that as a standard function I would have to write it out with a bunch
of comma separated arguments and include all the commas for the arguments I
don't use and all optional arguments would have to be specified at the end
of the function signature. I could use the named argument syntax with a
standard function and "almost" do it the same as with the class, but its
just nicer to be able to use the class syntax.

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

[Keith Wilby]

Re: Custom Classes

"jlepack" <jlepack@gmail. comwrote in message
news:1164895226 .867182.261250@ 80g2000cwy.goog legroups.com...

>
Take an Employee for example. I am an employee, you presumably are an
employee.
>
At the root, all employees have a first name, last name, birthdate,
SSN, etc. You could store each of those variables and have a
JasonLepack as Employee, or a KeithWilby as Employee.
>

Any chance of posting an example Jason?

Keith.

[Keith Wilby]

Re: Custom Classes

"Rick Brandt" <rickbrandt2@ho tmail.comwrote in message
news:JSCbh.1435 $Py2.203@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.

[Gord]

Re: Custom Classes


Keith Wilby wrote:

"Rick Brandt" <rickbrandt2@ho tmail.comwrote in message
news:JSCbh.1435 $Py2.203@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]

Re: Custom Classes

"Gord" <gdt@kingston.n etwrote in message
news:1164904204 .500707.221050@ 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]

Re: Custom Classes

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" <rickbrandt2@ho tmail.comwrote in message
news:JSCbh.1435 $Py2.203@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]

Re: Custom Classes

Keith Wilby wrote:

"Gord" <gdt@kingston.n etwrote in message
news:1164904204 .500707.221050@ 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@FortuneJames.com]

Re: Custom Classes

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
CDMAPoster@Fort uneJames.com