How does synchronous and asynchronous programming differ in iOS? What are the tradeoffs in using each?

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Anonymous · Accepted Answer

sync is when the code is executed in the order that it's written in, async means
that the code inside the async block is run on a separate thread, and the
programmer can't rely on the code running in the sequence it was written in.
usually, for async, there's a callback method that the thread will execute after
the async functionality returns. sync is used generally for code that needs to
run in order, and async is used for actions that can take some indeterminant
amount of time to come back, such as IO, networking, or graphics related
functionality. a special thread on ios is main, which is the only thread that
can execute UI related code. It's important to make sure you only update the UI
from the main thread, otherwise your app will crash. So, for example if your
code uses a different thread to get data from your backend async (because it
will take time for the request to return), you'll have to call the main thread
to update with the data after your request comes back.

How does synchronous and asynchronous programming differ in iOS? What are the tradeoffs in using each?

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