WPF Canvas-based ItemsControl with minimum recycled items?

Question

I'm using an ItemsControl with a Canvas as its backing Panel. I often need to .Clear() the ObservableCollection is the ItemsControl's ItemSource, and then add new information to it, which causes all the controls to be destroyed and new UserControls to be created, which is very sluggish. How can I force the ItemsControl to retain a certain amount of containers even after I call .Clear(), and then reuse them when new items are added to the ItemSource?

Answer 1

I am not sure how efficient this would be in your use case, but you might create a derived ItemsControl and override the GetContainerForItemOverride and ClearContainerForItemOverride methods to put and take item containers from a cache collection.

public class CachingItemsControl : ItemsControl
{
    private readonly Stack<DependencyObject> itemContainers =
        new Stack<DependencyObject>();

    protected override DependencyObject GetContainerForItemOverride()
    {
        return itemContainers.Count > 0
            ? itemContainers.Pop()
            : base.GetContainerForItemOverride();
    }

    protected override void ClearContainerForItemOverride(
        DependencyObject element, object item)
    {
        itemContainers.Push(element);
    }
}