In my “Why should I use MVVM pattern” post, I gave a link to a post explaining the ICollectionView interface.

This interface is very important in the MVVM methodology because it enables the possibility to track the selection of the user in ItemsControl based-controls (ListView, ListBox, ComboBox, TabControl…). The ICollectionView also enables the ViewModel to perfom Sorting, Grouping and Filtering very easily (basically by using the Sort, Group and Filter properties).

In my project at work, I have a “Library” which lets the user choose an item in it, and drop it somewhere else in the application. There is around 200 items in the ListView, and because I wanted to leverage the ICollectionView interface, I used the Filter property to enable search functionality.Unfortunately, the performance was pretty poor and until now I didn’t find out what goes wrong. Each item in the ListView is rendered using a simple DataTemplate made of one Image and several TextBlock. Because the filtering was slow, I found another solution which is much faster. And thanks to the MVVM methodology, I found one quickly !

I added a IsVisible property to the ViewModel objects that are in the ListView.

        /// 

        /// Gets or sets a value indicating whether this item is visible in the collection
        /// 
        public bool IsVisible
        {
            get { return this.isVisible; }
            set
            {
                this.isVisible = value;
                this.OnPropertyChanged("IsVisible");
            }
        }

This IsVisible property is toggled when the search is performed: I iterate over the ObservableCollection of items, and change the IsVisible property regarding whether the item match the search text or not. In the View, I setup a simple style for my ListViewItem that databound the IsVisible property to the visibility property (using the BooleanToVisiblity converter included in the framework).

Now the filtering is much faster. I don’t know what could slow down the performance of the filtering using the ICollectionView interface.

If you have any idea, I’d be glad to know. If on the other hand you’re dealing with performance issue too, you might try my solution 🙂