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759

answers:

1

Hello all,

I have a ListBox with way too many items in it and the UI is getting slower and slower (virtualization is on, etc). So I was thinking about displaying only the first 20 items and allow to user to navigate through the result set (i.e. ObservableCollection).

Does anybody know if a Pagination mechanism exist for the ObservableCollection? Does anybody has done that before?

Thanks!

+1  A: 

This facility is not directly available in the base ObservableCollecton class. You can extend the ObservableCollection and create a custom Collection which does this. You need to hide the original Collection inside this new class and based on a FromIndex and ToIndex give dynamically add the range of items to the class. Override InsertItem and RemoveItem. I am giving a not-tested version bellow. But please take this as just pseudo code.

 //This class represents a single Page collection, but have the entire items available in the originalCollection
public class PaginatedObservableCollection : ObservableCollection<object>
{
    private ObservableCollection<object> originalCollection;

    public int CurrentPage { get; set; }
    public int CountPerPage { get; set; }

    protected override void InsertItem(int index, object item)
    {
        //Check if the Index is with in the current Page then add to the collection as bellow. And add to the originalCollection also
        base.InsertItem(index, item);
    }

    protected override void RemoveItem(int index)
    {
        //Check if the Index is with in the current Page range then remove from the collection as bellow. And remove from the originalCollection also
        base.RemoveItem(index);
    }
}

UPDATE: I have a blog post about this topic on here - http://jobijoy.blogspot.com/2008/12/paginated-observablecollection.html and the source code is uploaded to Codeplex.

Jobi Joy
That's a good idea. I like the concept, but we are duplicating objects in memory, no?
Martin
No we are not duplicating the objects. Suppose if there are 10 pages with 10 items in each page. the originalCollection would have 100 items and we just refer only 10 to this Paginatedcollection.
Jobi Joy