I’m trying to understand the structure of the NSOperationQueue blocks on pp.436-437.
There seem to be three nested blocks here. The outer two of which involve the processingQueue object; the inner one uses the mainQueue. What is the logic for this choice please?
Presumably the inner block has to use the mainQueue because it involves the user interface (presenting the images and displaying text).
But why have the outer blocks been structured in this way? Why use 3 blocks and not 2, or even 4?
Many thanks in advance!