When you start iOS When developing , You will soon realize the importance of persistence in building applications . But in Swift When saving data in , What options do you have ？ How do you decide which one to use ？ Let's take a look at some of the most common , So you can make a wise decision , And can effectively save your data in Swift in ！

What is data persistence ？

Through data persistence , You can save data on some kind of storage medium . This may be something like a hard disk drive or a cloud server , Information can be stored and retrieved at will . How do we use Swift Save the data ？ ok , It depends on the persistence of the information you want to save .Swift There are three different types of data persistence methods in ： Read files from disk 、 Store objects in NSUserDefaults And will be Core Data For more complex applications . In addition to these three methods , There are other ways to store information for later use （ For example, using iCloud）. however , These are beyond the scope we will cover here .

Why do we need data persistence ？

The answer is simple . If you are with IOS Cooperation for a period of time , You will know that users can exit your application at any time , Then return later . You also know , When the user exits your application , He / All her unsaved changes will be lost , This can be very frustrating for users who spend a lot of time on your application . To overcome these types of situations , We need some kind of data persistence mechanism , Our data can be persisted beyond the life cycle of the application , So that it can be reloaded later when the application needs .

Different types of data persistence methods

Swift There are many different ways to save data , Each method has its own advantages and disadvantages . for example , You can store data as user defaults (plist) Or use JSON file . Besides , There are several other options for storing various types of data , for example XML