Collection byRef? 1

[stnkyminky]

First off let me say that anyone who helps explain why this is happening will receive a star.

I've got several classes(Publication and Ad). The publication class contains information about a trade magazine(name, issue date). The Ad class contains information about an Ad that is in a magazine(name, products mentioned, etc)

I have a public property in the Publication class that is an Ad Collection (Ads). When I populate the publication class, I also load all of the ads in that issue. I have a function that returns an Ad Collection (Ads) and it is assigned in a For Loop ----->

pub(i).Ads = GetAds(pub(i).ID)

I then take the Publication Collection (Publications) and add the objects to a combo box via For Each loop

dim pub as Publication
dim pubs as Publications
pubs = GetPublications()
for each pub in pubs
ComboBox1.Items.Add(pub)

Within the GetPublications function was a call to a separate sub that would add the Ads to the Publication Object

          count = col.Count - 1
            For i = 0 To count
                col(i).Ads = obj.getAds(col(i).ID)
            Next

Now, when the user clicks on a publication (SelectedIndexChange Event), I take the SelectedItem in the combo box and iterate through the Ads and add them to a separate combo box

  cboItem.Items.Clear()
            _ads = CType(cboPub.SelectedItem, LeadSystem.BAL.Publication).Ads

            If _ads.Count > 0 Then
                For i = 0 To count
                    cboItem.Items.Add(_ads(i))
                Next
            Else
                cboItem.Enabled = False
                cboItem.Items.Add("No Ads Available")
            End If
            cboItem.SelectedIndex = 0

The code above existed in Try..Catch. In the Finally statement I would do the following

_ads.clear()
_ads = Nothing

Clicking through each item in the publication combo box worked great and returned the ads in that publication. After reaching the last item, I then tried to access the first item in the publication combo. At that point the Ads collection in the Publication object was Nothing. I wasn't altering the code anywhere in the form.

Just as a stab to fix the problem. I removed code that would "Clear" the collection (code above). After commenting out that code, the ads are retained. My questions is this.

Scott
Programmer Analyst
<{{><

 

[RiverGuy]

Hmmmm. Your question is what? Left that part out!

 

[stnkyminky]

Wow....guess I was trying to give too much detail and forgot the important things.

When the code below is commented I don't have problems. Otherwise I'm able to cycle through the Ad objects in the Publication once and then the Ad objects are equal to nothing.

_ads.clear()
_ads = Nothing

Scott
Programmer Analyst
<{{><

 

[JohnYingling]

You voluntarily wiped out the original collection.
_ads conatins a reference to the original collection.

ads = CType(cboPub.SelectedItem, LeadSystem.BAL.Publication).Ads

therfore _ads.clear() is the same as saying

CType(cboPub.SelectedItem, LeadSystem.BAL.Publication).Ads.Clear

The _ads = Nothing is ok because it only sets a variable containig a reference to the collection to nothing.

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