Questions about refreshing the interface UI after a network request

There is a problem with the project. The synchronization request cannot refresh the interface.

???? Originally conceived: In the method of synchronizing the request, before synchronizing the request, add a chrysanthemum. The sync request gets the result and then the chrysanthemum is removed.

???? Reality: Chrysanthemums do not show at all. The pit.

???? Since then a whole day's struggle began. Later asked a friend. Say it's a synchronous request freeze interface, let me try it with an asynchronous request. Later, after the asynchronous request network, in the main thread refresh interface, it is possible.

???? I still don't understand Apple's frozen view, so why? A friend knows the answer and helps out. Thank you.

Questions about refreshing the interface UI after a network request