Correct handling of NSJSONSerialization (try catch) in Swift (2.0)?

Question

arowmy init works fine in Swift < 2 but in Swift 2 I get a error message from Xcode Call can throw, but it is not marked with 'try' and the error is not handled at let anyObj = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers) as! [String:AnyObject]. I think in my case I can´t use a try catch block because super is not initialized at this time. "Try" need a function that throws.

here is my function:

required init(coder aDecoder : NSCoder) {     self.name  = String(stringInterpolationSegment: aDecoder.decodeObjectForKey("name") as! String!)     self.number = Int(aDecoder.decodeIntegerForKey("number"))     self.img = String(stringInterpolationSegment: aDecoder.decodeObjectForKey("image") as! String!)     self.fieldproperties = []      var tmpArray = [String]()     tmpArray = aDecoder.decodeObjectForKey("properties") as! [String]       let c : Int = tmpArray.count     for var i = 0; i < c; i++     {         let data : NSData = tmpArray[i].dataUsingEncoding(NSUTF8StringEncoding)!           // Xcode(7) give me error: 'CAll can thorw, but it is not marked with 'try' and the error is not handled'         let anyObj =  NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers) as! [String:AnyObject]          let label = anyObj["label"] as AnyObject! as! String         let value = anyObj["value"] as AnyObject! as! Int         let uprate = anyObj["uprate"] as AnyObject! as! Int         let sufix = anyObj["sufix"] as AnyObject! as! String          let props = Fieldpropertie(label: label, value: value, uprate: uprate, sufix: sufix)         self.fieldproperties.append(props)     } } 

Xcode mean that: let anyObj = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers) as! [String:AnyObject]

but I have no idea to do here the right think according to this document https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/ErrorHandling.html

Answer 1

The jsonObject can throw errors, so put it within do block, use try, and catch any errors thrown. In Swift 3:

do {     let anyObj = try JSONSerialization.jsonObject(with: data) as! [String: Any]      let label = anyObj["label"] as! String     let value = anyObj["value"] as! Int     let uprate = anyObj["uprate"] as! Int     let sufix = anyObj["sufix"] as! String      let props = Fieldpropertie(label: label, value: value, uprate: uprate, sufix: sufix)      // etc. } catch {     print("json error: \(error.localizedDescription)") } 

Or, in Swift 4, you can simplify your code by making your struct conform to Codable:

struct Fieldpropertie: Codable {     let label: String     let value: Int     let uprate: Int     let suffix: String } 

Then

do {     let props = try JSONDecoder().decode(Fieldpropertie.self, from: data)     // use props here; no manual parsing the properties is needed } catch {     print("json error: \(error.localizedDescription)") } 

For Swift 2, see previous revision of this answer.