Adding a range of values to an ObservableCollection efficiently

Question

I have an ObservableCollection of items that is bound to a list control in my view.

I have a situation where I need to add a chunk of values to the start of the collection. Collection<T>.Insert documentation specifies each insert as an O(n) operation, and each insert also generates a CollectionChanged notification.

Therefore I would ideally like to insert the whole range of items in one move, meaning only one shuffle of the underlying list, and hopefully one CollectionChanged notification (presumably a "reset").

Collection<T> does not expose any method for doing this. List<T> has InsertRange(), but IList<T>, that Collection<T> exposes via its Items property does not.

Is there any way at all to do this?

Answer 1

The ObservableCollection exposes an protected Items property which is the underlying collection without the notification semantics. This means you can build a collection that does what you want by inheriting ObservableCollection:

class RangeEnabledObservableCollection<T> : ObservableCollection<T> {     public void InsertRange(IEnumerable<T> items)      {         this.CheckReentrancy();         foreach(var item in items)             this.Items.Add(item);         this.OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));     } } 

Usage:

void Main() {     var collection = new RangeEnabledObservableCollection<int>();     collection.CollectionChanged += (s,e) => Console.WriteLine("Collection changed");     collection.InsertRange(Enumerable.Range(0,100));     Console.WriteLine("Collection contains {0} items.", collection.Count);   } 

Answer 2

To make the above answer useful w/o deriving a new base class using reflection, here's an example:

public static void InsertRange<T>(this ObservableCollection<T> collection, IEnumerable<T> items) {   var enumerable = items as List<T> ?? items.ToList();   if (collection == null || items == null || !enumerable.Any())   {     return;   }    Type type = collection.GetType();    type.InvokeMember("CheckReentrancy", BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.NonPublic, null, collection, null);   var itemsProp = type.BaseType.GetProperty("Items", BindingFlags.NonPublic | BindingFlags.FlattenHierarchy | BindingFlags.Instance);   var privateItems = itemsProp.GetValue(collection) as IList<T>;   foreach (var item in enumerable)   {     privateItems.Add(item);   }    type.InvokeMember("OnPropertyChanged", BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.NonPublic, null,     collection, new object[] { new PropertyChangedEventArgs("Count") });    type.InvokeMember("OnPropertyChanged", BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.NonPublic, null,     collection, new object[] { new PropertyChangedEventArgs("Item[]") });    type.InvokeMember("OnCollectionChanged", BindingFlags.Instance | BindingFlags.InvokeMethod | BindingFlags.NonPublic, null,      collection, new object[]{ new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset)}); }