I have an array of objects each with a number of properties. Here is some sample data taken by looping through the array of objects:
Name = Rent
Default Value 750
This Months Estimate = 750
Sum Of This Months Actuals = 0
Risk Factor = 0.0
Monthly Average = 750.0
--------------
Name = Bills
Default Value 250
This Months Estimate = 170
Sum Of This Months Actuals = 140
Risk Factor = 0.0
Monthly Average = 190.0
--------------
Name = Food
Default Value 240
This Months Estimate = 200
Sum Of This Months Actuals = 95
Risk Factor = 0.0
Monthly Average = 190.0
--------------
Name = Lunches
Default Value 100
This Months Estimate = 150
Sum Of This Months Actuals = 155
Risk Factor = 0.899999976158142
Monthly Average = 190.0
Its very little data so I want to avoid using core data. I need to be able to persist save the array then open it again and be able to loop through it. I was hoping to use a simple solution like NSUserDefaults or NSKeyedArchiver but in Swift I can get neither to work with this type of array (I've been going through documentation and forums and examples online for 24 hours now...)
How would you recommend I persist save an array of objects like the above? OR maybe persist saving this type of array is bad practice?
Thanks in advance for your help!
Adding the object class:
class costCategory : NSObject {
var name : String
var defaultValue : Int
var thisMonthsEstimate : Int
var sumOfThisMonthsActuals : Int
var riskFactor : Float
var monthlyAverage : Float
init (name:String, defaultValue:Int, thisMonthsEstimate:Int, sumOfThisMonthsActuals:Int, riskFactor:Float, monthlyAverage:Float) {
self.name = name
self.defaultValue = defaultValue
self.thisMonthsEstimate = thisMonthsEstimate
self.sumOfThisMonthsActuals = sumOfThisMonthsActuals
self.riskFactor = riskFactor
self.monthlyAverage = monthlyAverage
}
}
If I try to save the array to NSUserDefaults I'm getting the error:
Property list invalid for format: 200 (property lists cannot contain objects of type 'CFType')
I have tried using inheriting from the NSCoder class but I get an error which Im not able to resolve, as below:
class costCategory : NSObject, NSCoder {
var name : String
var defaultValue : Int
var thisMonthsEstimate : Int
var sumOfThisMonthsActuals : Int
var riskFactor : Float
var monthlyAverage : Float
init (name:String, defaultValue:Int, thisMonthsEstimate:Int, sumOfThisMonthsActuals:Int, riskFactor:Float, monthlyAverage:Float) {
self.name = name
self.defaultValue = defaultValue
self.thisMonthsEstimate = thisMonthsEstimate
self.sumOfThisMonthsActuals = sumOfThisMonthsActuals
self.riskFactor = riskFactor
self.monthlyAverage = monthlyAverage
}
// MARK: NSCoding
required convenience init(coder decoder: NSCoder) {
self.init() //Error here "missing argument for parameter name in call
self.name = decoder.decodeObjectForKey("name") as String
self.defaultValue = decoder.decodeIntegerForKey("defaultValue")
self.thisMonthsEstimate = decoder.decodeIntegerForKey("thisMonthsEstimate")
self.sumOfThisMonthsActuals = decoder.decodeIntegerForKey("sumOfThisMonthsActuals")
self.riskFactor = decoder.decodeFloatForKey("riskFactor")
self.monthlyAverage = decoder.decodeFloatForKey("monthlyAverage")
}
func encodeWithCoder(coder: NSCoder) {
coder.encodeObject(self.name, forKey: "name")
coder.encodeInt(Int32(self.defaultValue), forKey: "defaultValue")
coder.encodeInt(Int32(self.thisMonthsEstimate), forKey: "thisMonthsEstimate")
coder.encodeInt(Int32(self.sumOfThisMonthsActuals), forKey: "sumOfThisMonthsActuals")
coder.encodeFloat(self.riskFactor, forKey: "riskFactor")
coder.encodeFloat(self.monthlyAverage, forKey: "monthlyAverage")
}
}
One possibility is to convert your object properties:values to string:object store them to NSUserDefaults and then get and decode them back.
If you want to store your object using NSKeyedArchiver, your class needs to conform to NSCoding and be subclass of NSObject. Example:
class costCategory : NSObject, NSCoding {
var name : String
var defaultValue : Int
var thisMonthsEstimate : Int
var sumOfThisMonthsActuals : Int
var riskFactor : Float
var monthlyAverage : Float
init (name:String, defaultValue:Int, thisMonthsEstimate:Int, sumOfThisMonthsActuals:Int, riskFactor:Float, monthlyAverage:Float) {
self.name = name
self.defaultValue = defaultValue
self.thisMonthsEstimate = thisMonthsEstimate
self.sumOfThisMonthsActuals = sumOfThisMonthsActuals
self.riskFactor = riskFactor
self.monthlyAverage = monthlyAverage
}
// MARK: NSCoding
required init(coder decoder: NSCoder) {
//Error here "missing argument for parameter name in call
self.name = decoder.decodeObjectForKey("name") as String
self.defaultValue = decoder.decodeIntegerForKey("defaultValue")
self.thisMonthsEstimate = decoder.decodeIntegerForKey("thisMonthsEstimate")
self.sumOfThisMonthsActuals = decoder.decodeIntegerForKey("sumOfThisMonthsActuals")
self.riskFactor = decoder.decodeFloatForKey("riskFactor")
self.monthlyAverage = decoder.decodeFloatForKey("monthlyAverage")
super.init()
}
func encodeWithCoder(coder: NSCoder) {
coder.encodeObject(self.name, forKey: "name")
coder.encodeInt(Int32(self.defaultValue), forKey: "defaultValue")
coder.encodeInt(Int32(self.thisMonthsEstimate), forKey: "thisMonthsEstimate")
coder.encodeInt(Int32(self.sumOfThisMonthsActuals), forKey: "sumOfThisMonthsActuals")
coder.encodeFloat(self.riskFactor, forKey: "riskFactor")
coder.encodeFloat(self.monthlyAverage, forKey: "monthlyAverage")
}
}
Then you can archive and save to NSDefaults:
let defaults = NSUserDefaults.standardUserDefaults()
let arrayOfObjectsKey = "arrayOfObjectsKey"
var arrayOfObjects = [costCategory]()
var arrayOfObjectsData = NSKeyedArchiver.archivedDataWithRootObject(arrayOfObjects)
defaults.setObject(arrayOfObjectsData, forKey: arrayOfObjectsKey)
// ...
var arrayOfObjectsUnarchivedData = defaults.dataForKey(arrayOfObjectsKey)!
var arrayOfObjectsUnarchived = NSKeyedUnarchiver.unarchiveObjectWithData(arrayOfObjectsUnarchivedData) as [costCategory]
Core Data is incredibly powerful and I highly recommend you try not be swayed by its intimidating appearance. When your app grows you will be incredibly grateful that you backed your data with Core Data as it scales incredibly well.
That being said, theres a nice article on NSHipster that covers the basics of using the NSKeyedArchiver. So the solution would be to have your objects be a subclass of NSObject and conform to the NSCoding protocol. This allows you to archive an unarchive the objects from the disk. You can the save your file to the documents directory
Your subclass would then need to implicitly unwrap all the encode-able variables, the result would yield:
class costCategory : NSObject, NSCoding {
var name : String!
var defaultValue : Int!
var thisMonthsEstimate : Int!
var sumOfThisMonthsActuals : Int!
var riskFactor : Float!
var monthlyAverage : Float!
init (name:String, defaultValue:Int, thisMonthsEstimate:Int, sumOfThisMonthsActuals:Int, riskFactor:Float, monthlyAverage:Float) {
self.name = name
self.defaultValue = defaultValue
self.thisMonthsEstimate = thisMonthsEstimate
self.sumOfThisMonthsActuals = sumOfThisMonthsActuals
self.riskFactor = riskFactor
self.monthlyAverage = monthlyAverage
}
override init() {
super.init()
}
// MARK: NSCoding
required convenience init(coder decoder: NSCoder) {
self.init()
self.name = decoder.decodeObjectForKey("name") as String
self.defaultValue = decoder.decodeIntegerForKey("defaultValue")
self.thisMonthsEstimate = decoder.decodeIntegerForKey("thisMonthsEstimate")
self.sumOfThisMonthsActuals = decoder.decodeIntegerForKey("sumOfThisMonthsActuals")
self.riskFactor = decoder.decodeFloatForKey("riskFactor")
self.monthlyAverage = decoder.decodeFloatForKey("monthlyAverage")
}
func encodeWithCoder(coder: NSCoder) {
coder.encodeObject(self.name, forKey: "name")
coder.encodeInteger((self.defaultValue), forKey: "defaultValue")
coder.encodeInteger((self.thisMonthsEstimate), forKey: "thisMonthsEstimate")
coder.encodeInteger((self.sumOfThisMonthsActuals), forKey: "sumOfThisMonthsActuals")
coder.encodeFloat(self.riskFactor, forKey: "riskFactor")
coder.encodeFloat(self.monthlyAverage, forKey: "monthlyAverage")
}
}
You could then add a way of finding the location to the documents directory:
func documentsDirectory() -> NSString {
let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
let documentDirectory = paths[0] as String
return documentDirectory
}
So archiving would look like this:
var filePath = documentsDirectory().stringByAppendingPathComponent("fileName")
NSKeyedArchiver.archiveRootObject(receipts, toFile: filePath)
and later on you could read your array back from disk:
let receipts = NSKeyedUnarchiver.unarchiveObjectWithFile(filePath)
I would recommend against using User Defaults to store an array, its meant to store preferences, here take a look at the documentation:
The NSUserDefaults class provides a programmatic interface for interacting with the defaults system. The defaults system allows an application to customize its behavior to match a user’s preferences. For example, you can allow users to determine what units of measurement your application displays or how often documents are automatically saved. Applications record such preferences by assigning values to a set of parameters in a user’s defaults database.
Ideally you don't want to persist arrays because then you have to fetch the entire array into memory even if you need one object. Naturally Core Data will solve all that unnecessary heap mess for you:)
EDIT
To ease yourself into Core Data you could always look at Magical Record. They simplify a lot of the cruft needed to maintain the Core Data stack.
Good Luck
Core Data Evangelist
来源：https://stackoverflow.com/questions/26233067/simple-persistent-storage-in-swift