When a table view asks for a cell, often images in the cell isn’t yet available and needs to be fetched from a server – thus the cell gets a placeholder image. But static placeholders doesn’t look as good as animated ones. Unfortunately cell views gets scrolled off and re-used which makes managing animations challenging.
The pervasive use of blocks and new nested context in iOS 5 and Mac OS X Lion paved the path to a whole new way of multithreading. Apple has lifted yet another barrier to use Core Data for applications that needs to run on multiple threads. This article teach you how to effectively write multi-threaded apps that uses Core Data as it’s backing store.
Core Data isn’t thread safe and Apple recommends to use multiple contexts instead to handle concurrency. However Apple seems to have forgotten that on Mac OS X, there are hooks like the undo manager that can cause havoc in multi-threaded Core Data applications, even each thread having its own context.