[AccessD] Advanced Unbound Form With Classes andCollectionsPart 3

Like on DatabaseAdvisor's web site?

;-)

John W. Colby
Colby Consulting
www.ColbyConsulting.com

-----Original Message-----
From: accessd-bounces at databaseadvisors.com
[mailto:accessd-bounces at databaseadvisors.com] On Behalf Of William Hindman
Sent: Tuesday, June 27, 2006 11:39 PM
To: Access Developers discussion and problem solving
Subject: Re: [AccessD] Advanced Unbound Form With Classes andCollectionsPart
3

Drew

...this is pretty good stuff ...do you intend to post it elsewhere as a
single article?

William

----- Original Message -----
From: "JWColby" <jwcolby at colbyconsulting.com>
To: "'Access Developers discussion and problem solving'" 
<accessd at databaseadvisors.com>
Sent: Tuesday, June 27, 2006 8:08 PM
Subject: Re: [AccessD] Advanced Unbound Form With Classes and
CollectionsPart 3


> Drew,
>
>>Public Function NewEnum() As Iunknown
>
> Is this a dedicated syntax thing or can I do this multiple times for 
> multiple collections in the same class?
>
> Public Function NewEnum1() As IUnknown
>
> Set NewEnum1=PeopleByFirst.[_NewEnum1]
>
> End Function
>
> Public Function NewEnum2() As IUnknown
>
> Set NewEnum2=PeopleByLast.[_NewEnum2]
>
> End Function
>
> John W. Colby
> Colby Consulting
> www.ColbyConsulting.com
>
> -----Original Message-----
> From: accessd-bounces at databaseadvisors.com
> [mailto:accessd-bounces at databaseadvisors.com] On Behalf Of 
> DWUTKA at marlow.com
> Sent: Tuesday, June 27, 2006 2:58 PM
> To: accessd at databaseadvisors.com
> Subject: [AccessD] Advanced Unbound Form With Classes and Collections 
> Part
> 3
>
> We have built a 'collection class' in our demo, the People Class.  It 
> is an object representing all of the people in our database.  We can 
> retrieve people from it either with their ID, or by their sort order 
> (first or last name sort).
>
>
>
> But why can't we do a For Next loop?  I mean, our class represents 
> multiple Persons, so it contains all of the Person classes, why are we 
> forced to use an index or position to retrieve a person?
>
>
>
> Surprise, we're not.  Though to get this capability requires a little 
> 'outside of the box' work.  Here's what we need to do.  First, we need 
> to add a function to our People class:
>
>
>
> Public Function NewEnum() As IUnknown
>
> Set NewEnum=PeopleByFirst.[_NewEnum]
>
> End Function
>
>
>
> The next portion is a little tricky in Access.  We need to set this 
> procedure's 'id' to -4.  In Visual Basic 6, you can do this by 
> clicking
> Tools>Procedure Attributes, and then clicking the Advanced button.  I
> looked, couldn't find this in Access, but all's not lost.  We can 
> still do this.  Right click on the People class in our demo project's code
window.
> Select Export File.  Save it somewhere.  Now go and open that saved 
> file in Notepad.  You'll see the code of our class with some extra 
> stuff thrown in.
> What we need to do is add a line in our NewEnum function so it looks 
> like
> this:
>
>
>
> Public Function NewEnum() As IUnknown
>
> Attribute NewEnum.VB_UserMemId = -4
>
> Set NewEnum=PeopleByFirst.[_NewEnum]
>
> End Function
>
>
>
> Once this is done, let's test it.
>
>
>
> Create a form with a button, and put the following code behind it:
>
>
>
> Dim ps as Person
>
> Dim ppl as People
>
> Set ppl=New People
>
> For Each ps in ppl
>
>            Debug.print ps.FullName
>
> Next
>
> Set ps=nothing
>
> Set ppl=nothing
>
>
>
> Now press the button and run our test code.  Whalla!  We can now loop 
> through the Person objects in our People Collection with a For Next loop!
>
>
>
> So now that we know about collections, and we have created the same 
> functionality of a collection with our own 'collection class', let's 
> go a step further, and make our Person class 'aware' of it's collection
class.
> We'll do this in the next part.
>
>
>
> Drew
>
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