The incoming NotifyCollectionChangedEventArgs parameter defines two important properties, OldItems and NewItems , which will give you a list of items that were currently in the collection before the event fired, and the new items that were involved in the change. However, you will want to examine these lists only under the correct circumstances. Recall that the CollectionChanged event can fire when items are added, removed, relocated, or reset. To discover which of these actions triggered the event, you can use the Action property of NotifyCollectionChangedEventArgs. The Action property can be tested against any of the following members of the NotifyCollectionChangedAction enumeration:
Old English hwilc (West Saxon) "which," short for hwi-lic "of what form," from Proto-Germanic *khwilikaz (cf. Old Saxon hwilik , Old Norse hvelikr , Swedish vilken , Old Frisian hwelik , Middle Dutch wilk , Dutch welk , Old High German hwelich , German welch , Gothic hvileiks "which"), from *khwi- "who" (see who ) + *likan "body, form" (cf. Old English lic "body;" see like (adj.)). In Middle English used as a relative pronoun where Modern English would use who , as still in the Lord's Prayer. Old English also had parallel forms hwelc and hwylc , which disappeared 15c.
In that context, a national survey of 1,520 adults conducted March 7-April 4, 2016, finds that Facebook continues to be America’s most popular social networking platform by a substantial margin: Nearly eight-in-ten online Americans 1 (79%) now use Facebook, more than double the share that uses Twitter (24%), Pinterest (31%), Instagram (32%) or LinkedIn (29%). On a total population basis (accounting for Americans who do not use the internet at all), that means that 68% of all . adults are Facebook users, while 28% use Instagram, 26% use Pinterest, 25% use LinkedIn and 21% use Twitter.