ListView with scroll events and TopItem

Tue, February 22, 2005, 02:09 PM under MobileAndEmbedded
Two years ago I asked the question:
"I cannot find an event to catch when the user scrolls the scrollbar? The goal is to detect when the listview is scrolled and then get all visible items (or just the top one and work my way down since I know how many can be visible at a time) and do some function..."
I then replied to my own post.

The simple idea of overlaying the listview with a vscrollbar works great and is an important technique for CF lists with a large number of items (for memory and performance improvements). What I am trying to say is that, rather than populate your list with XXX number of items, you need only populate the visible (e.g. 8-16) items and when the user scrolls down populate accordingly the remainder (since you know the top index and the number of visible items at any one time).

The same principle, but with a twist, applies when the listviewitems need to be refreshed/updated every so often. E.g. my listviews get populated with information retrieved from the network. By knowing which items are visible, I avoid refreshing the ones that are not, resulting in faster user interaction and less noise on the network. By also wrapping the refresh timer into the container control, the rest of the client code is oblivious to how the list gets populated.

Finally, you could offer explicit pageup/pagedown buttons (since you are in programmatic control of the scrolling). A screen shot of what such a listview looks like see this (the statusbar of that screenshot is a whole different story :-).

Enjoy the code from the link at the top of this post and if you need the same for a ListControl rather than a listview, follow the link from here.
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