在Swift(2.0)中正确处理NSJSONSerialization(try catch)？

Question

arowmy初始化工作正常斯威夫特<2,但是在斯威夫特2我从Xcode中的错误消息Call can throw, but it is not marked with 'try' and the error is not handled的let anyObj = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers) as! [String:AnyObject].我认为在我的情况下我不能使用try catch块,因为此时super尚未初始化."尝试"需要一个抛出的功能.

这是我的功能:

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

但根据这份文件,我不知道在这里做正确的思考https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/ErrorHandling.html

Answer 1

该jsonObject罐throw的错误,所以把它内do块,使用try和catch出现的任何错误.在Swift 3中:

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)")
}

或者,在Swift 4中,您可以通过使struct符合以下内容来简化代码Codable:

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

然后

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)")
}

对于Swift 2,请参阅此答案的先前版本.

Answer 2

JSONSerialization.JSONObject抛出ErrorType而不是NSError.

所以正确的捕获是

do {
    let anyObj = try JSONSerialization.JSONObject(with: data, options: []) as! [String:AnyObject]
    // use anyObj here
} catch let error {
    print("json error: \(error)")
}

errorin 的类型catch let error是ErrorType