My IF condition executes inconsistently - DESPERATELY NEED HELP :-( 2

[DotNetter]

I've spent hours and hours on this and would be most grateful if someone could help me get some sleep.

I've got the following two subs:

	Private Sub EraseAllAccountRelatedControls()
		
		Dim x As String	'dummy value

		Dim ctl As Control
		For Each ctl In Controls

			If ctl Is Nothing = False Then

				If (ctl.Name = "AccountsControl" And TypeOf ctl Is AccountsControl) Or (ctl.Name.ToLower.StartsWith("account_")) Or (TypeOf ctl Is PropertiesControl AndAlso CType(ctl, PropertiesControl).PropertyCollection.ClassName.ToUpper <> "USER INFORMATION") Then
					'x = ctl.Name 'this is just a placeholder - this variable is insignificant
					'DeleteControl(ctl.Name)
				End If

			End If

		Next

	End Sub

	Private Sub DeleteControl(ByVal ControlName As String)

		Dim ctl As Control
		For Each ctl In Controls
			If ctl Is Nothing = False AndAlso ctl.Name = ControlName Then
				Me.Controls.Remove(ctl)
			End If
		Next

	End Sub

My problem is in the first sub. Please note the two lines in that first sub:[tt]
x = ctl.Name
DeleteControl(ctl.Name)[/tt]
(I am aware that they are both currently commented-out.)

Me.Controls.Count = 13 when this first sub executes. What I need to have in the first sub is the "DeleteControl(ctl.Name)" line. When I put it in, it does not loop through all 13 controls. In other words, I have a breakpoint on the "Next" in that first sub, and am watching the value of ctl.Name there ...and some of my 13 controls never show up there (i.e. their names don't appear in the value of ctl.Name when that breakpoint is hit.)

When I switch out that line for the "x = ctl.Name" line - a dummy/test line - then I do see my ctl.Name value for the control I'm looking for when the breakpoint is hit.

Something about that call of "DeleteControl(ctl.Name)" makes it not loop through all of the controls... I know my IF conditions look a bit intimidating, but I don't think the problem is there, since when I have that dummy "x = ctl.Name" line - it is executed at exactly the correct times. (If only the real line would act the same!)

Please, please, please help...

Thanks so much,
Dot

 

[ThatRickGuy]

are any of your controls in a panel or group box?

-Rick

VB.Net Forum forum796 forum855 ASP.NET Forum
I believe in killer coding ninja monkeys.

 

[RoyVidar]

There's something fishy going one when you're both looping a collection, and removing items from it. I think it's probably safer to use the index, and start at "the end" of the collection in stead, see thread796-1076604.

Roy-Vidar

 

[earthandfire]

The problem is to do with indexing. When you remove a control from the collection the collection automatically reindexes.

As Roy says you need to iterate backwards through the collection using something like:

dim ctrl as control
for a as integer = me.controls.count - 1 to 0
ctrl = me.controls(a)
if ctrl <meets deletion criteria> then
me.controls.removeat(a)
end if
next

typed NOT tested


Hope this helps.

 

[DotNetter]

Roy and EarthAndFire,

Thank you very much for answering my plea for help! Unfortunately, it didn't quite work. This is what I tried: I left sub "[tt]EraseAllAccountRelatedControls[/tt]" exactly as I have it above. I changed sub "[tt]DeleteControl[/tt]" per your suggestions, as follows:

	Private Sub DeleteControl(ByVal ControlName As String)

		Dim ctl As Control
		For a As Integer = Me.Controls.Count - 1 To 0
			ctl = Me.Controls(a)
			If ctl Is Nothing = False AndAlso ctl.Name = ControlName Then
				Me.Controls.RemoveAt(a)
			End If
		Next

	End Sub

When I step through it in the debugger, the first time execution hits the sub, it hits the "For a ..." line, then the "End Sub" line - and that's it. It's so weird how the "Next" line isn't even hit once!

I would greatly appreciate some more of your kind help...

Thanks,
Dot

 

[earthandfire]

My mistake:

For a As Integer = Me.Controls.Count - 1 To 0 Step - 1


Sorry

 

[RoyVidar]

[tt]For a As Integer = Me.Controls.Count - 1 To 0 Step -1[/tt]

Roy-Vidar

 

[chiph]

There's something fishy going one when you're both looping a collection, and removing items from it.

Yes. You shouldn't do it.

The reason is that when you are simultaneously looping through a collection, and adding or deleting items from it, the .net iterator code gets confused. Take a look at the MSDN help for the MoveNext method on the IEnumerator interface (the interface that is used to iterate through an array or collection). It says:

An enumerator remains valid as long as the collection remains unchanged. If changes are made to the collection, such as adding, modifying or deleting elements, the enumerator is irrecoverably invalidated and the next call to MoveNext or Reset throws an InvalidOperationException.

Chip H.


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[earthandfire]

Chip, why, then, does my suggestion work - and not throw an exception?

 

[ThatRickGuy]

E&F you're not iterating through the collection, you are iterating through an integer value.

This is going to have issues with adding and removing controls:
For Each ctl In Controls

This is not:
For iCtl as Int = Controls.Count - 1 to 0 Step -1

-Rick

VB.Net Forum forum796 forum855 ASP.NET Forum
I believe in killer coding ninja monkeys.

 

[chrissie1]

e&f chiph is reffering to the for each next thingie. Not the for next loop

Christiaan Baes
Belgium

I just like this --> [Wiggle] [Wiggle]

 

[earthandfire]

I realised that as soon as I had hit submit - but thanks Rick.

 

[DotNetter]

I want to reiterate my appreciation for all of your help - thanks so much!

...but it's still not working properly. Maybe it has to do with what Chip wrote.

Here's what's going on: Sub "[tt]EraseAllAccountRelatedControls[/tt]" remains unchanged (i.e. as I posted it at the top of the thread). I changed the loop in "[tt]DeleteControls[/tt]" using "Step -1", as both of you suggested. (Again, I thank you!)

When I have the call to sub "[tt]DeleteControls[/tt]" from within sub "[tt]EraseAllAccountRelatedControls[/tt]", it (i.e. the "[tt]For Each[/tt]" loop in "[tt]EraseAllAccountRelatedControls[/tt]") does not iterate through all of the controls that it should; but when I uncomment the call to "[tt]DeleteControls[/tt]", it does...

Any further ideas, please???

Thanks!!!
Dot

 

[earthandfire]

Try

    Private Sub DeleteControl(ByVal ControlName As String)

        Dim ctl As Control
        For a As Integer = Me.Controls.Count - 1 To 0 Step -1
            ctl = Me.Controls(a)
            If (ctl.Name = "AccountsControl" And TypeOf ctl Is AccountsControl) Or (ctl.Name.ToLower.StartsWith("account_")) Or (TypeOf ctl Is PropertiesControl AndAlso CType(ctl, PropertiesControl).PropertyCollection.ClassName.ToUpper <> "USER INFORMATION") Then
              Me.Controls.RemoveAt(a)
            End If
        Next

    End Sub

Hope this helps.

 

[ThatRickGuy]

You need to change both of those loops to be integer iterators.

-Rick

VB.Net Forum forum796 forum855 ASP.NET Forum
I believe in killer coding ninja monkeys.

 

[DotNetter]

EarthAndFire,

I scrapped the two subroutine plan and combined them into one, as you did. And... It's perfect!!!

Rick, as far as your comment:

You need to change both of those loops to be integer iterators.

There's only one loop now.

Here's the final code:

Private Sub EraseAllAccountRelatedControls()

	Dim ctl As Control
	For ControlIndexIterator As Integer = Me.Controls.Count - 1 To 0 Step -1
		ctl = Me.Controls(ControlIndexIterator)
		If (ctl.Name = "AccountsControl" And TypeOf ctl Is AccountsControl) Or (ctl.Name.ToLower.StartsWith("account_")) Or (TypeOf ctl Is PropertiesControl AndAlso CType(ctl, PropertiesControl).PropertyCollection.ClassName.ToUpper <> "USER INFORMATION") Then
			Me.Controls.RemoveAt(ControlIndexIterator)
		End If
	Next

End Sub

And it works great!

I'm most grateful to everyone who participated! Stars to EarthAndFire and to Roy!!!

Thanks much!
Dot


Thank you

 

[DotNetter]

...so what is the answer to EarthAndFire's question:

Chip, why, then, does my suggestion work - and not throw an exception?

???
Dot

 

[earthandfire]

Dot, have a look at ThatRickGuy's and Chrissie1's replies - I was too quick asking the question - using:

for a as integer = etc.

is fine

ChipH was referring

for each etc.

Hope this helps.

 

[chiph]

Yeah, I seldom use the indexer-based loops. But this would be a good situation where you'd have to.

Chip H.


____________________________________________________________________
Donate to Katrina relief:

http://s1.amazon.com/paypage/PELYGQVJ8Q7IB/103-6821258-5919825

If you want to get the best response to a question, please read FAQ222-2244 first