Storing OpaquePointer type in UserDefaults - ios

Question

I am working on Xcode 12 and Swift 5 environment to build an iOS application.
I need to store an OpaquePointer type variable("self.loggers" in the code below) before the view disappears(or before the app closes) and retrieve it when the view appears( when the app runs).
I tried to use UserDefault as below,
// Storing(In viewWillDisappear)
do {
encodedData = try NSKeyedArchiver.archivedData(withRootObject: self.loggers, requiringSecureCoding: false)
UserDefaults.standard.set(encodedData, forKey: "accelLoggerID")
} catch {
print("archiving error")
}
...
// Retrieving(In viewDidLoad)
if let decodedData = UserDefaults.standard.object(forKey: "acceleration") as? Data {
do {
self.loggers = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(decodedData) as? [String:OpaquePointer] ?? [:]} catch {
print("unarchiving error")
}
} else {
self.loggers = [:]
print("No value in Userdefault. [viewDidLoad]")
}
However, NSKeyedArchiver failed to encode such type. After that, I made a class that wraps the variable.
class LoggerWrapper {
var loggers: [String : OpaquePointer]
init(loggerDic: [String : OpaquePointer]) {
loggers = loggerDic
}
}
And changed my code like
self.loggers = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(decodedData) as? LoggerWrapper ?? LoggerWrapper(loggerDic: [:])} catch {
print("unarchiving error")
}
However, this gives SIGABRT when NSKeyedArchiver.archivedData is called.
Is there any way to store Opaquepointer type in UserDefaults? If not, can using core data solve this problem?
Thank you.

Answer 1

You probably need to convert the pointers to Int bitPatterns. There is an initializer on Int for that: let intBitPattern = Int(bitPattern: opaquePointer).
There is also an initializer on OpaquePointer that takes an Int bitPattern: let opaquePointer = OpaquePointer(bitPattern: intBitPattern).
So you would need to convert the values in your dictionary (e.g. using compactMapValues) before storing and after reading it.
With a Dictionary<String, Int>, you should be able to store it directly in UserDefaults, without the need for NSKeyedArchiver and NSKeyedUnarchiver.
Sidenote:
Pointers aren't "long-lived". So storing it in UserDefaults is only valid during the lifetime of your app. Once your app restarts, the pointers might no longer be valid.