Tiny LRU cache implementation

LRUObservableCollection.cs

public class LRUObservableCollection<T> : ObservableCollection<T>
{
    private readonly int _length;

    public LRUObservableCollection(int length)
    {
        _length = length;
    }

    protected override void InsertItem(int index, T item)
    {
        base.InsertItem(index, item);
        if (Count > _length) RemoveAt(0);
    }
}