grand central dispatch

Last week,  through a mini project I got to work on GCD for the first time and all of the sudden it started making sense to me.


So the project loads a tableview of a list of Guests type.  In the cell,

1. on main thread, label loads the name of the guests from firebase , and the imageView loads a placeholder image temperily. 
2. and on the separated thread the photos of the guests(a cat picture in this sample) being loaded and replace the placeholder image once it is done downloading from Firebase storeage. 

https://github.com/lingzt/FirebaseDatabasePra