Question

How to enumerate a ListView when it is in virtual mode ?

I’m using OfType<>() method to enumerate the list view items. But its throwing an exception like, the list view can not be enumerated when it is in virtual mode.

Here is my code

List<String> lst= myListView.Items.OfType<ListViewItem>().Select(X=>X.Text).ToList(); 

So how do i get the item from the ListView when it is in Virtual mode?

Please post me a way to use .OfType<>

Thanks in advance

Answer 1

When it’s in virtual mode you can’t get the items out of the list view because the items aren’t in the list view. That’s the whole point of virtual mode.

Instead, you hold the items and the list view asks for the information it needs to display the items. If you are operating a list view successfully in virtual mode then you almost certainly already have the items in a list somewhere.

Quoting from the documentation:

Setting the VirtualMode property to
true puts the ListView into virtual
mode. In Virtual mode, the normal
Items collection is unused. Instead,
ListViewItem objects are created
dynamically as the ListView requires
them.

Virtual mode can be useful under many
circumstances. If a ListView object
must be populated from a very large
collection already in memory, creating
a ListViewItem object for each entry
can be wasteful. In virtual mode, only
the items required are created. In
other cases, the values of the
ListViewItem objects may need to be
recalculated frequently, and doing
this for the whole collection would
produce unacceptable performance. In
virtual mode, only the required items
are calculated.