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    <p>Good question. What you're seeing is to be expected, given the way the exercise is architected. The reason is that the animation (and drawing) of layers is done on the main thread, which is currently occupied loading images and creating thumbnails. It's not until all of the images have been loaded and the thumbnails have been created that the main thread can actually get around to performing the animation you requested. <code>CATransaction</code> doesn't have much of any impact in this single-threaded context.</p> <p>We improve upon this in the next chapter (34, Concurrency) by preparing the images in a background thread (using <code>NSOperationQueue</code>). This frees the main thread to display the new images and perform the animation as each image is loaded and resized in the background.</p>
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    1. USAdam Preble
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    1. COThanks, Adam. I appreciate it. I'm glad that the behavior is to be expected, at least by someone :-). I find it quite strange. It seems to me that each iteration of the `for(id url in urls)` loop should load an image and then animate the presentation of that image regardless of which thread is doing the work. It is not clear to me, either from the code or the `CATransaction` documentation, that the `CATransaction` calls might be ignored. I'll read that documentation more carefully soon though.
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    2. COI wouldn't say that they're being ignored, but more that they aren't getting a chance to take effect, since the main thread isn't getting a chance to handle other events (such as the animation) until after -addImagesFromFolderURL: returns. This is a common thing to watch out for in Cocoa (and other frameworks): allowing the main thread to resume so that the UI can update and respond to user input.
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    3. COThank you again! Now that I've finished the Concurrency chapter, however, I have to say that I'm still confused. All images still appear at once, though faster (2.0s vs 3.0s). The UI updates all-at-once as if I've committed only one animation. To me, though, it seems that I've committed multiple animations, one in each pass through the loop. How would I begin to make the images appear one-at-a-time? (I did try moving the `addImagesFromFolderURL` out of `applicationDidFinishLaunching` and instead made it the target of a button. Still had same results.)
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