Fill a List with Large Amount of Data – Part 2

Inserting a large number of items in a listview control, may take a lot of time.
A virtual list does not internally keep items information (like text and so on). Instead, it notifies its parent, asking info only for the items/subitems which are currently displayed. That makes it a good choyce if dealing with a large number of items.

Using a virtual list

  1. Set LVS_OWNERDATA style.
    First note this style cannot be set after control creation. For a listview control contained in a dialog resource, it can be done by setting True for Owner Data property. For a listview control kept by a CListView class, the right place is in the overridden PreCreateWindow
  2. Load data.
    May be, for example, an array of database records as a result of an SQL query. See the attached demo project for a concrete example.
  3. Set the virtual list items count.
  4. Finally, handle the LVN_GETDISPINFO notification.
    As said in the beginning, a virtual list doesn’t internally keep items info. Instead, it sends LVN_GETDISPINFO notification via WM_NOTIFY message, each time it needs info about the items to be actually displayed.
    For a listview control we can use the wizard to map LVN_GETDISPINFO in the parent dialog class or the reflected =LVN_GETDISPINFO notification, in a class derived from CListCtrl.
    In a class derived from CListView we can also use the wizard to map reflected =LVN_GETDISPINFO notification. 

    First argument is a pointer to a NMLVDISPINFO structure. From its member of type LVITEM, we can get which info is required (text, image, etc) and the index of item and subitem that is being displayed. Next, we have to fill that structure with the information from an external data collection.

Demo project

Download: Virtual_List_Demo.zip (1411)

The demo project uses the same SQL query to fill a non-virtual and a virtual listview. As can be seen in the screenshot, the virtual list worked over ten times faster.

Using Virtual List - Demo Application

Using Virtual List – Demo Application

 

Additional notes

  • The demo application uses an SQL Server Compact 4.0 database. Its runtime engine usually comes with Visual Studio 2012. Anyway, if it isn’t already installed on your machine, you can download it for free, from Microsoft Download Center:
    http://www.microsoft.com/en-us/download/details.aspx?id=17876
  • A future article will show how to improve the virtual listview control in order to deal with much larger amount of data, by caching.

Resources

See also

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