Unable to bridge NSNumber to Float

Question

I'm runtime errors on my existing project when migrating versions of Xcode. Can someone help with this? Is my typecasting wrong?

Code:

let x    = d[ChildItem.KEY_LOOK] as! NSArray as Array
let y    = d[ChildItem.KEY_COOR] as! NSArray as Array
let item = ChildItem(x as! [Float], y as! [Float])

Error:

Thread 5: Fatal error: Unable to bridge NSNumber to Float

I know how to cast an NSNumber to a Float as I found on SO (Unable to bridge NSNumber to Float in JSON parsing):

    if let n = d.value(forKey: "probability") as? NSNumber {
    let f = n.floatValue }

How can I do this for an NSNumber array?

In each of the d[] keys there are JSON strings like this:

d[ChildItem.KEY_LOOK] = [465918.2, 5681518.0,4462.3203]

I have to say, this is really ugly code. First of all, you should avoid force casting, that causes crashes. Then you're force-casting to `NSArray` and then to `Array`, when casting to `NSArray` is unnecessary. `KEY_LOOK` and `KEY_COOR` are plain ugly to look at, I would create a `Key` enum in `ChildItem` and add constants in there, so it'd look like this `ChildItem.Key.Look`. And finally, we don't know how `d` is declared, or how you got it's contents, so we can only guess what your error is, you should provide us with that info and avoid using NS-prefixed classes when working with Swift. — EmilioPelaez, Aug 14 '18 at 17:31
@Vadian - you can see contents of 'd' at the SO post: https://stackoverflow.com/questions/49610727/unable-to-bridge-nsnumber-to-float-in-json-parsing — Fra, Aug 14 '18 at 18:18
I mean the `d` in your first example. And `value(forKey...as NSNumber)` is horrible code. — vadian, Aug 14 '18 at 18:26
@Vadian - d content: d["s_i_coord"]. What it is is going through a JSON tree. — Fra, Aug 14 '18 at 18:33
Sorry, I'm out. Without knowing the **real** contents of `d` (and its static type) I can't help. — vadian, Aug 14 '18 at 18:40
What happens if you skip the first cast to NSArray and just have `let x = d[ChildItem.KEY_LOOK] as? Array` — Joakim Danielson, Aug 14 '18 at 18:40
@JoakimDanielson Type cast to `Array` is pointless. A JSON array is at least `[Any]`, in many cases `[[String:Any]]` and in this particular case it's supposed to be `[Float]`. — vadian, Aug 14 '18 at 18:43
@vadian, yes of course. I didn't think that through, I guess I just got frustrated by the double casting. — Joakim Danielson, Aug 14 '18 at 18:45
I also tried: let y = d[ChildItem.KEY_COOR] as! [Float] and get same error. — Fra, Aug 14 '18 at 18:47
Unless you clarify your question and show us what kind of data you have in `d` for those two keys this is pointless. Also in your question you say you're having problem compiling the project but this is a runtime error, very confusing and what is this about "...migrating versions if Xcode"? — Joakim Danielson, Aug 14 '18 at 18:53

score 0 · Answer 1 · answered Aug 14 '18 at 16:58

0

you need to use the floatValue property of NSNumber, not casting directly.

answered Aug 14 '18 at 16:58

Gabriel Vieira

67
4

How would the syntax be written to do this on an Array? – Fra Aug 14 '18 at 17:00
1

Can you provide me with sample code? I'd be grateful. – Fra Aug 14 '18 at 17:07
something like this? let num = NSNumber(value: 8) let arr = [num,num,num,num,num] let result = arr.map{ $0.floatValue } – Gabriel Vieira Aug 14 '18 at 17:46
Basically you should not use `NSNumber` in Swift at all unless the API requires it. This API certainly doesn't. (I didn't downvote by the way) – vadian Aug 14 '18 at 17:49

score -1 · Answer 2 · answered Aug 15 '18 at 03:52

Let's say you have an array of numbers you got from the server calls like this

d[ChildItem.KEY_LOOK] = [465918.2, 5681518.0,4462.3203] // from your example

you can do the following

//As from your example that can be directly convert to Array of Doubles like this
if let arrayOfDoubles = d[ChildItem.KEY_LOOK] as? [Double] {
        debugPrint(arrayOfDoubles)
}

And if for some reason you want those to be [NSNumber] then you can do like this

if let arrayOfNumbers = d[ChildItem.KEY_LOOK] as? [NSNumber] {

        //to make this array of double
     let doubleArray = arrayOfNumbers.map { $0.doubleValue }

        //to make int
     let intArray = arrayOfNumbers.map { $0.intValue }

     ... and so on
}

Unable to bridge NSNumber to Float

2 Answers2