user defaults swift 3 save for different users

The current section requires basic understanding of property wrappers. Now that we know what is UserDefaults, let’s do some actual work and implement key-value storage, based on UserDefaults and property wrappers. UserDefaults has two levels of caching: the domain level and the app level.

It reads and writes XML files to the disk and does the caching. The app preferences delegate per-domain work to CFPreferences.c. CFApplicationPreferences manages the dictionary representation of user defaults across all registered domains with some caching involved. When we set a value to UserDefaults, it calls _CFApplicationPreferencesSet from CFApplicationPreferences.c, which is a bunch of scary C code with some comments dated 1999. UserDefaults performs best when the writes are rare and reads are frequent. This gives us another insight about the user defaults performance: The dictionary is re-computed each time the value is added, updated or removed from the user defaults. The domains from the search list are merged into a single dictionary, which is an expensive operation. We are free to add more domains if we want more granular control over UserDefaults storage. The search list is initialized when we read or write values for the first time. Both names refer to the same concept, so we’ll continue calling it domain.īy default, every app has 8 domains, which are organized into the so-called search list. If you peek into UserDefaults internals, you’ll discover that it’s also called suite. plist file, where the associated data is persisted.ĭomain is just a plain string. This means that each domain has a corresponding. UserDefaults saves data on a per-domain basis. Let’s dig into swift-corelibs-foundation to find out how UserDefaults works behind the scenes. Arbitrary data types will likely become incompatible with newer versions of your app.Īccording to Apple, the best approach to UserDefaults is to store user preferences and app configuration as simple values.Arbitrary data types must be archived and unarchived to and from Data, which is expensive.It is also not recommended to store custom objects for the following reasons: plist file per domain (and typically per app), which becomes bloated if we store big chunks of data there. The reason for that is that the defaults use a single. Nonetheless, it is not recommended to store large chunks of data, because reads and writes become more expensive the more data UserDefaults contains. There is no hard limit on the size of data that we can store to UserDefaults, except for the 1MB on tvOS. Here is the full list of supported types from the UserDefaults source code: common Swift types, uncommon Swift types, NS- / CF- bridging types, plus NSNumber (non-bridging, but still supported). It is also possible to store arbitrary objects by encoding them into a Data object first. UserDefaults storage is limited to the so-called property-list data types : Data, String, Date, Bool, Int, Double, Float, Array, Dictionary and URL (the only non-property-list-type). UserDefaults manages the persistent storage of key-value pairs in a. Design type-safe key-value storage, based on UserDefaults and Swift property wrappers.How UserDefaults is implemented internally?.What kind of data should we save to UserDefaults?.

The introduction of property wrappers in Swift 5 offers a great opportunity to revisit the conventional approach to UserDefaults and freshen the fundamentals along the way. The Swift language evolves quickly, bringing new features into the play and changing the ways we used to work with the existing ones. UserDefaults has been around in iOS SDK for as long as anyone can recall.

User defaults swift 3 save for different users