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Improve component appearance and disappearance events

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Description

enhancement

Appearance/disappearance events can be inconsistent and unreliable, likely due to the fact they are typically driven by the underlying UICollectionView. We should investigate better alternatives that satisfy the following properties:

  1. Components that are added while a tree is onscreen should receive a -[CKComponentController componentTreeWillAppear] event
  2. Components that are removed while a tree is onscreen should receive a -[CKComponentController componentTreeDidDisappear] event
  3. There should be a guaranteed balance between both events; a-[CKComponentController componentTreeWillAppear] event should be followed by at most one -[CKComponentController componentTreeDidDisappear] event
Dominant language
Objective-C++
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