问题

I have a Swift struct like this.

struct Usage {
    var totalData: Double
    var remainingTotalData: Double

    init(jsonData: NSData) {
        var jsonDict = [String: AnyObject]()

        do {
            jsonDict = try NSJSONSerialization.JSONObjectWithData(jsonData, options: []) as! [String: AnyObject]
        } catch {
            print("Error occurred parsing data: \(error)")
        }

        totalData = jsonDict["totalfup"] as! Double
        remainingTotalData = jsonDict["totalrem"] as! Double
    }
}

From an API, I get the following JSON response. This is the println of the jsonDict variable.

[
    "totalfup": 96.340899, 
    "totalrem": 3548710948
]

When I try to assign the value of the totalfup to the property totalData, I get this error.

Could not cast value of type 'NSTaggedPointerString' to 'NSNumber'

Anyone knows why? I tried changing the property type to float and then the whole struct to class but still the issue occurs.

回答1:

The reason of the error is jsonDict["totalfup"] is a String (NSTaggedPointerString is a subclass of NSString) , so you should convert String to Double.

Please make sure, catch exception and check type before force-unwrap !

totalData = (jsonDict["totalfup"] as! NSString).doubleValue

For safety, using if let:

// check dict["totalfup"] is a String?
if let totalfup = (dict["totalfup"] as? NSString)?.doubleValue {
  // totalfup is a Double here 
}
else {
  // dict["totalfup"] isn't a String
  // you can try to 'as? Double' here
}

回答2:

I think this could help you

totalData = Double(jsonDict["totalfup"] as! String)!

回答3:

The failure reason is that the JSON returns String values, not numbers.

If the returned JSON data contains only these two key value pairs declare the type as [String:String] that avoids the type casting.

In any case you have to put the code to update the variables into the "good" branch of the do - catch expression.

struct Usage {
    var totalData = 0.0
    var remainingTotalData = 0.0

    init(jsonData: NSData) { // Swift 3: Data

        do {
            let jsonDict = try NSJSONSerialization.JSONObjectWithData(jsonData, options: []) as! [String: String]                
            // Swift 3: let jsonDict = try NSJSONSerialization.jsonObject(with: jsonData) as! [String: String]
            totalData = Double(jsonDict["totalfup"]!)
            remainingTotalData = Double(jsonDict["totalrem"]!)
        } catch {
            print("Error occurred parsing data: \(error)")
        }
    }
}

回答4:

why not use Swift's native types directly?

import Foundation

struct Usage {
    var totalData: Double = 0
    var remainingTotalData: Double = 0

    init(jsonData: NSData) {
        do {
            if let jsonDict = try NSJSONSerialization.JSONObjectWithData(jsonData, options: []) as? [String:Double] {
                totalData = jsonDict["totalfup"] ?? 0
                remainingTotalData = jsonDict["totalrem"] ?? 0
            }
        } catch {
            print("Error occurred parsing data: \(error)")
        }
    }
}

if let data = "{\"totalfup\":96.340899,\"totalrem\":3548710948}".dataUsingEncoding(NSUTF8StringEncoding) {
    let usage = Usage(jsonData: data)
    dump(usage)
    /*
    ▿ Usage
      - totalData: 96.340899
      - remainingTotalData: 3548710948.0
    */
}

回答5:

Swift 4

    let strStatus:String = dictProperty.value(forKey: "StatusType") as! String
    let myStatus = Double.init(strStatus)

Update

extension String {
    func toDouble() -> Double? {
        let numberFormatter = NumberFormatter()
        numberFormatter.locale = Locale(identifier: "en_US_POSIX")
        return numberFormatter.number(from: self)?.doubleValue
    }

    func toInt() -> Int? {
        let numberFormatter = NumberFormatter()
        numberFormatter.locale = Locale(identifier: "en_US_POSIX")
        return numberFormatter.number(from: self)?.intValue
    }

    func toFloat() -> Float? {
        let numberFormatter = NumberFormatter()
        numberFormatter.locale = Locale(identifier: "en_US_POSIX")
        return numberFormatter.number(from: self)?.floatValue
    }

    func toBool() -> Bool? {
        let numberFormatter = NumberFormatter()
        numberFormatter.locale = Locale(identifier: "en_US_POSIX")
        return numberFormatter.number(from: self)?.boolValue
    }
}

来源：https://stackoverflow.com/questions/33299202/could-not-cast-value-of-type-nstaggedpointerstring-to-nsnumber

标签

ios

swift

double

nsjsonserialization