将Strutts的Swift结构数组转换为NSArray时反之亦然的问题

Question

I'm running into the problem of bridging Swift arrays of Structs to NSArrays. I want to store a Swift Array of Structs in NSUserDefaults. NSUserDefaults will only accept an NSArray. Can somebody tell me whether this is the correct way of doing it:

First I declare an array some SwiftStruct and use it in my program:

var favorites = [SomeSwiftStruct]()

Then to store it I have to turn it into an NSArray. The only way to have the compiler not complain is to upcast it as follows:

let tempArray = favorites as Any as NSArray
let defaults = NSUserDefaults.standardUserDefaults()
defaults.setObject(tempArray, forKey: "favorites")

Then retrieving it I wanted to try this:

if let tempArray = defaults.objectForKey("favorites") as NSArray as Any as? [SomeSwiftStruct]{
  favorits = tempArray}

Unfortunately I can't yet test whether this works. For now I only know there are no compiler complaints

Answer 1

The problem is, the thing the compiler is complaining about is that you are doing something that won't work. You cannot store non-Objective-C objects (including structs) in an NSArray . Going via Any is adding enough obfuscation that the compiler stops complaining, but doesn't fix the issue.

The reason it compiles is that your second as is a forcing cast, ie Swift will do it no matter whether its valid or not. But this is dangerous, since it will not work at runtime, all you'll get is an assertion. In fact, in the current 1.2 version of Swift that's in beta, this kind of as has been renamed as! to indicate that it is dangerous like this.

To store stuff in NSUserDefaults you're doing to have to have a method on your Swift struct that renders it into something that can be stored (for example, an array of strings, which will be convertible to an NSArray of NSString s).