You may notice that a download completion alert message pops up well before the images have finished downloading:
Run the app, tap +, and select Le Internet to add internet photos. Alternatively, you can use the Download Materials button at the top or bottom of this tutorial to download the starter project. You can pick up where you left off with the sample project from part one if you followed along. It’s time to explore some more GCD! Getting Started You’ll delve into advanced GCD concepts including dispatch groups, canceling dispatch blocks, asynchronous testing techniques, and dispatch sources. In this second Grand Central Dispatch tutorial, you’ll be working with the same GooglyPuff application you know and love from the first part. You also enhanced the app’s UX by using dispatch queues to delay the display of a prompt and to asynchronously offload CPU-intensive work when instantiating a view controller. You made a singleton thread safe for reading and writing using a combination of dispatch barriers and synchronous dispatch queues. In the first part of this series, you learned about concurrency, threading, and how GCD works. Welcome to the second and final part of this Grand Central Dispatch tutorial series! Update note: Evan Dekhayser updated this tutorial to Swift 4.2.
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