Virtual List Controls (MFC)

Question

I am using a List Control to display a representation of elements within a vector. When the list is clicked on another control shows information about that element. The index of the element is currently determined by its index in the control, however if I wish to sort or filter the results this will no longer work.

I have been told that I could use a virtual list control, but the MSDN is not very friendly, can someone run me through how I could use a virtual list control for this?

Thanks! :)

Answer 1

Frankly - tying data (the position in your data vector) to the presentation of the data in the list control (the position in the list ctrl) is something I would stay away from.

In MFC each control has a "Data" DWORD member variable - when coding in MFC I Always called "SetItemData" for each item added and passed in a pointer that the relevant row referred to e.g. YourListCtrl.SetItemData((DWORDPTR)&YourData);

Then when the ListCtrl item is selected, you just call

DataTypeYouWant* pData = (DataTypeYouWant*)(YourListCtrl.GetItemData(indexofselecteditem));

Or somesuch thing.

Alternatively - if you don't want to use pointers - hold the index of the item in your original vector in the itemdata for your row (just pass it into the above fns).

Answer 2

To use a virtual list control, set the LVS_OWNERDATA style. You then need to handle the LVN_GETDISPINFO notification message (which is sent via WM_NOTIFY).

If you do this, you are entirely responsible for the data, including the order in which it is shown. Therefore it is up to you to handle sorting and so forth.

By far the easiest way is just to use the item data to set/get an ID that can be used to retrieve the original data, whether that's a vector index or a pointer to the data, or even a key into an associative container.

Answer 3

It really depends on the performance you require.

I have personally seen MAJOR increases in performance for lists holding massive amount of data. However it is much more work to implement, thus for simple uses with not so many data I recommend staying away from it.

Basically, what happens with virtual list controls is that you have your data somewhere in some data structure of your own. Since the list view shows only a small subset of the whole data, it queries you for the content to display when ever something happens (redraw necessary, scroll up or down, change the sorting, etc.).

I don't have handy examples for you. But you can look on codeguru, I am quite sure there are very good examples to start from.

Answer 4

The purpose of virtual list controls is totally different: You should use it for performance reason when you have A LOT of items in your list (I'd say 2500+).

In your case, all you need is to store the vector index in the list item data as NotJarvis explains.