Re: Explanation of ListView in virtual mode

I agree, the virtual thing is definitely supposed to be ideal for these
conditions...  

Well, you should probably do a quick test with 20/1000 and see what
happens.  I've seen quite a few articles saying that for extremely large
lists, virtual mode is thousands of times faster, so I'd definitely try
to see for myself.  The only real problem I can see with
RetrieveVirtualItem being called so many times would be a performance
issue, but if your tests were to show that it ends up being faster
anyways, then there is no real problem.

-- Daniel.

-----Original Message-----
From: Discussion forum for developers using Windows Forms to build apps
and controls [mailto:[email protected]] On Behalf Of
Richard Kucia
Sent: 07 August 2007 05:47 PM
To: [email protected]
Subject: Re: [DOTNET-WINFORMS] Explanation of ListView in virtual mode

Yes, it's the RetrieveVirtualItem event that has me puzzled.

I have in mind an application which would use the ListView in several
very different places. This test was for one of them, where the exact
number of items is known and permanently fixed (20/64). However, I
foresee a different usage, where historical realtime event data is
appended to the ListView, and the number of events tracked can easily
reach 1000 or more. So the virtual concept is perfect for that sort of
thing, but if I'm having these problems with a setup of 20/64, I guess I
won't need to explore 20/1000....

Rick


-------------- Original message from Daniel Barla-Szabo
<[email protected]>: --------------


> Hi,
>
> > The event handler that sends a ListViewItem
>
> I'm guessing you are referring to the RetrieveVirtualItem event?
>
> I threw together a quick test app here, and I'm seeing similar things
to
> you... Perhaps even more strange is that if I hover my mouse over an
item,
> the event just keeps firing. Perhaps it fires when Paint() is
triggered?
>
> This might seem like a cheesy opt-out, but do you predict that your
ListView
> will grow in number of records? 64 rows by 20 columns should perform
OK
> using VirtualMode = false, or am I wrong? Depending on your exact
> situation, it might be better to use the standard setup.
>
> Regards,
>
> Daniel.
>
>
> -----Original Message-----
> From: Discussion forum for developers using Windows Forms to build
apps and
> controls [mailto:[email protected]] On Behalf Of
Richard
> Kucia
> Sent: 07 August 2007 03:58 PM
> To: [email protected]
> Subject: [DOTNET-WINFORMS] Explanation of ListView in virtual mode
>
> I am experimenting with the ListView in virtual mode. I have data for
64
> rows and a visible area for 20 rows. The ListView has 9 columns.
>
> The event handler that sends a ListViewItem includes a Debug.Writeline
> statement, which I included just to see how .Net is invoking the event
> handler. To my surprise, there's a very definite pattern. It invokes
the
> handler 12 consecutive times for item #0, then 12 consecutive times
for item
> #1, ..., down to item #19.
>
> What's it doing? Why can't it just accept the item I returned upon the
first
> invocation?
>
> Rick Kucia
>
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