如何在Swift中将NSMutableArray传递为对NSMutableDictionary部分的引用？

Question

class PLCalendarEventViewController: UITableViewController {
    var event: NSMutableDictionary!

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == PLCalendarEditEventLinksSegueIdentifier {
            let tvc = segue.destinationViewController as PLCalendarEditEventLinksTableViewController
            if var links = event.objectForKey("links") as? NSMutableArray {
                tvc.data = links
            }
        }
    }
}

But inside my PLCalendarEditEventLinksTableViewController , when I try data.addObject("new link") then I get following error:

mutating method sent to immutable object .

All I need to do is when I change my NSMutableArray inside PLCalendarEditEventLinksTableViewController I change event: NSMutableDictionary inside PLCalendarEventViewController

class PLCalendarEditEventLinksTableViewController: UITableViewController {
    var data = NSMutableArray()
}

It is very simple in Objective-C, but how to do this in Swift?

Answer 1

This problem can be reproduced with this simple script:

import Foundation

let userDefault = NSUserDefaults.standardUserDefaults()

let obj: NSMutableDictionary = ["test": NSMutableArray(array: ["foo", "bar"])]
userDefault.setObject(obj, forKey: "key")

let obj2 = userDefault.objectForKey("key") as NSMutableDictionary
if let ary = obj2["test"] as? NSMutableArray {
    ary.addObject("baz")
}

You can store NSMutableArray to NSUserDefaults , but when retrieve it from that, it is actually a immutable array. see the docs :

Values returned from NSUserDefaults are immutable , even if you set a mutable object as the value.

I don't know how actually event constructed, but regardless of that, you have to deep copy it to mutable containers. AFAIK, the easiest way to do that is using CFPropertyListCreateDeepCopy() . At where you construct event property:

event = CFPropertyListCreateDeepCopy(nil, event, CFPropertyListMutabilityOptions.MutableContainers.rawValue) as NSMutableDictionary