Reading objects will never fail but return default values if the key does not exist:
integer(forKey:) returns an integer if the key existed, or 0 if not.
bool(forKey:) returns a boolean if the key existed, or false if not.
float(forKey:) returns a float if the key existed, or 0.0 if not.
double(forKey:) returns a double if the key existed, or 0.0 if not.
When retrieving objects, the result is optional. This means you can either accept the optionality, or typecast it to a non-optional type and use the nil coalescing operator to handle missing values. For example object(forKey:) returns AnyObject? so you need to conditionally typecast it to your data type:
let savedArray = defaults.object(forKey: "SavedArray") as? [String] ?? [String]()
5 Property Lists
Property lists are XML files that comply to Apple's PropertyList DTD
An example for a property list is the Info.plist file that resides in all app projects
To create your own .plist file go in the Xcode menu to File->New->File->Resource->Property List
6 Property Lists
To access a property file within the app project use:
let path =Bundle.main.path(forResource: "myprop", ofType: "plist")
let dict =NSDictionary(contentsOfFile: path!)
Now you can read the contents like:
// reading a String itemlet tableData = dict!.object(forKey: "testitem") as!String// reading an Array of Stringslet devices = dict!.object(forKey: "devices") as! [String]
7 Property Lists
To write to a property file, it needs to be loaded into a mutable dictionary
// load the property filelet writableProp =NSMutableDictionary(contentsOfFile: path!)
// change a value
writableProp?.setValue("Ansgar Gerlicher", forKey: "Name")
// write the property file atomically
writableProp?.write(toFile: path!, atomically: true)
8 Core Data
Core Data is an ORM framework to persist objects in iOS
To activate it just check the CoreData box, when creating your app project
This will add some extra code to your AppDelegate class allowing you to access the NSPersistentContainer instance to read and store data
9 Core Data
In order to read and store data using Core Data the following steps are necessary:
Create a Data Model using the integrated Data Model editor in XCode (here we create a Person entity):
Inside your ViewController (or whereever you need to access your data model):
Import CoreData
Obtain an reference to the NSPersistentContainer instance and to the persistence context (viewContext) for this container:
let appDelegate =UIApplication.shared.delegate as!AppDelegatelet container = appDelegate.persistentContainer
let context = container.viewContext
10 Core Data
With Xcode version > 8.0 the classes for the entities that are defined in the model editor are automatically generated in the background.
Thus it is very easy to create a new instance of our Person class and set it's properties:
let person =Person(context: context)
person.name ="Ansgar R. S. Gerlicher"
person.age =22
11 Core Data
In order to save the data persistently all you need to do is call save()on the context:
To read stored data from the context, you need to use the NSFetchRequest class to define what objects you want to read
Then use the fetch()function to load the objects from the store
let request : NSFetchRequest<Person> =Person.fetchRequest()
do {
let result =try context.fetch(request)
for personObject in result {
print(personObject)
}
} catch {
print("Loading Person failed")
}
13 Summary
In order to persist data on an iOS device you have many options:
Little information such as settings can be stored using the NSUser Defaults
App specific information and predefined data can be stored in Property list files
Images and binary data can be stored on the file systems
App specific data or user generated data can be stored in databases using Core Data ORM framework
