投射为？ Swift中的Int”对于不同的数字产生不同的结果

Question

I have an iOS app that worked fine, until at some point it started crashing on a nil value for a certain number.

After doing some tests in my code I managed to boil it down to the following piece of code that yields an output that does not make sense to me at all:

let tc: AnyObject? = jsonObject["times_completed"]
let pos: AnyObject? = jsonObject["position"]

println("TC FROM JSON \(tc)")
println("POS FROM JSON \(pos)")

println("TC TYPE: \(_stdlib_getDemangledTypeName(tc))")
println("POS TYPE: \(_stdlib_getDemangledTypeName(pos))")

let tcInt = tc as? Int
let posInt = pos as? Int

println("TC TYPE: \(_stdlib_getDemangledTypeName(tcInt))")
println("POS TYPE: \(_stdlib_getDemangledTypeName(posInt))")

println("TC: \(tcInt)")
println("POS: \(posInt)")

Output:

TC FROM JSON Optional(648)
POS FROM JSON Optional(6)

TC TYPE: Swift.Optional<Swift.AnyObject>
POS TYPE: Swift.Optional<Swift.AnyObject>

TC TYPE: Swift.Optional<Swift.Int>
POS TYPE: Swift.Optional<Swift.Int>

TC: nil
POS: Optional(6)

As you can see we have two Int s here, from which one ends up being nil (TC) and the other one end up holding the expected value (POS).

Since the code has always worked, I suspect that the number itself may be a problem (too high?).

Casting the Int in a different way helps, like so:

let tcInt = tc?.integerValue

But that would mean I have to resubmit my app, which will take some time. I would like to avoid that, maybe by (temporarily) changing the values for times_completed

Can anybody explain what happens here? Thanks.

---

UPDATE:

Please also check a piece of the JSON below. It seems that it is not a string, but a number. The key is a string, but would that matter?

...
position = 6;
slug = "my-quiz";
"times_completed" = 648;
...

Answer 1

It seems that your jsonObject["times_completed"] is a string and not a number.

And because .integerValue works for you proves it because its an NSString property.

And casting a String to an Int will crash.

You can also do it like this:

let tcInt = (jsonObject["times_completed"] as? String)?.toInt()

Answer 2

I think that jsonObject["times_completed"] is returning a String value and treating String like an Int in let tcInt = tc as? Int let tcInt = tc as? Int is causing a problem. Note that

var a : AnyObject? = 10
var b : AnyObject? = "10"

println(a)
println(b)

prints Optional(10) in both cases. Try casting it as String and check the results let tcInt = tc as? String let tcInt = tc as? String . If thats correct don't worry, your app isn't crashing because of your fault and maybe something in backend changed

Answer 3

The result of nil is probably because jsonObject["times_completed"] can not be cast to Int. Try to cast it to String or other Type.

if let tcStr = jsonObject["times_completed"] as? String {
    // string...
}