Question

NSUserDefaults is persistent right? If we close application it’s still there. So it’s IO.

Does that mean everytime we do

– setObject:forKey: we do IO?

Does iPhone will read and write to disk everytime we do

[[NSUserDefaults standardUserDefaults] setObject:trimmedSearchLocation forKey:SEARCHNEAR];

or that sort of thing

Answer 1

From the docs:

At runtime, you use an NSUserDefaults object to read the defaults that your application uses from a user’s defaults database. NSUserDefaults caches the information to avoid having to open the user’s defaults database each time you need a default value. The synchronize method, which is automatically invoked at periodic intervals, keeps the in-memory cache in sync with a user’s defaults database.

so only if synchronize invokes you have IO on your disk!