Question

I’m interested the most efficient way to change an observable collection in such a way that only one property changed is fired. Lets say that I want to populate the list with 3 items, there is no addCollection method or something like that, so I have to do clear + 3 times add. Do I need to create a different observable collection and assign? Or what techniqies do others use?

Answer 1

NET Framework’s ObservableCollection class sends individual notifications on as each item added to the collection and provides no mechanism for AddRange-type functionality. However you can very easily create your own collection that implements INotifyCollectionChanged and send whatever notifications you like.

On issue you may encounter is that the INotifyCollectionChanged interface includes the ability to specify that multiple items were added to the collection in a single message, but no standard NET Framework classes actually create these notifications. Because of this, some third-party and open source controls that assume only one item has been added when they receive an Add notification. Even the built-in NET Framework classes may have undiscovered bugs related to this.

For these reasons I would recommend your custom collection have a mode in which it can be set to always send a Reset notification at the end of an AddRange instead of a single multi-item Add notification. You could optimize this further by sending multiple single-item Add notifictions or a Reset notification depending on the actual number of items added.

Of course there are situations in which it is just as easy to replace the ObservableCollection with a new one. At times this will be much less efficient than looping Add() because event handlers and CollectionViews are rebuilt. Other times it will be more efficient if the collection is large and your loop only adds a few items at a time.
And sometimes it won’t work at all.