Question

Why ObservableCollection doesn’t has the RemoveAll method like a List?

I have implemented an extension method to provide this functionality to the ObservableCollection, but I would like to understand if there is a specific reason for not providing this functionality.

Would it possibly effect Data Binding in some way due to Collection change? This post does specify a few things that could go wrong while using ObservableCollections, but does not address this question.

Answer 1

It does have a Clear() method that removes all items that you can use instead.

If I had to hazard a guess as to why they used Clear instead of RemoveAll, I think it would be because RemoveAll carries the suggestion that you are removing items from the collection, while Clear tells you the items are simply being cleared.

This makes a difference in the type of CollectionChanged notification that gets raised. Clear() raises a NotifyCollectionChangedAction.Reset event and does not include the removed items in the event, while Remove raises a NotifyCollectionChangedAction.Removed event, and passes the removed item to the event.

You cannot raise a CollectionChanged event with multiple items, so raising a NotifyCollectionChangedAction.Removed event with all the items removed would throw an exception. The alternative would be to raise a CollectionChanged event for every item that got removed, which can be quite bad for performance. And simply raising a NotifyCollectionChangedAction.Reset event would cause some confusion when users are expecting a Removed event to occur when they are removing items.

So I am guessing they decided to simply use .Clear() instead of .RemoveAll() because the name is a better description of what is actually happening behind the scenes.