Pass a variable from foreground to background in Swift

Question

I am developing an iOS application where I want to record the time when a user presses a particular button and keep it. Later I will use this time record in background. Is there a nice way of doing that without invoking NSUserDefaults or CoreData or whatever other database?

I am very new to iOS development. I think this is very likely to be a naive question. But I'm just curious. Please don't laugh at me haha.

Edit: This is indeed a very naive question haha.

Answer 1

A simple way to make sure your data is available everywhere in your app and only persists for each app session would be to use a singleton. Something like this.

// Create a class to store the data
class SessionData : NSObject {

    // Create a shared instance of your class
    static let sharedInstance = SessionData()

    // Create a variable to store the date object
    var timeStore:NSDate?
}

This will mean that anywhere in your app you can get and set this data as below.

// Get
if let time = SessionData.sharedInstance.timeStore {
    println(time)
}

// Set
SessionData.sharedInstance.timeStore = NSDate()

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It is worth mentioning that despite the above being a valid method, You may be able to avoid doing this by re-thinking your app structure and passing data between classes instead. You should have a look at Delegation.

Also as @CouchDeveloper mentions in their comment below, you may want to included a dispatch queue to prevent crashes or locks in the situation where two or more classes try to read and or write data at the same time.