Swift、NSJSONSerialization 和 NSError

Question

问题是当数据不完整时 NSJSONSerialization.JSONObjectWithData 使应用程序崩溃并给出 unexpectedly found nil while unwrapping an Optional value 错误而不是使用 NSError 变量通知我们。所以我们无法防止崩溃。

您可以在下面找到我们正在使用的代码

      var error:NSError? = nil

      let dataToUse = NSJSONSerialization.JSONObjectWithData(receivedData, options:   NSJSONReadingOptions.AllowFragments, error:&error) as NSDictionary

    if error != nil { println( "There was an error in NSJSONSerialization") }

到目前为止我们还找不到解决方法。

Answer 1

问题是您将 JSON 反序列化的结果投射到之前检查错误。如果 JSON 数据无效（例如不完整）则

NSJSONSerialization.JSONObjectWithData(...)

returns nil 和

NSJSONSerialization.JSONObjectWithData(...) as NSDictionary

会崩溃。

这是一个正确检查错误条件的版本：

var error:NSError? = nil
if let jsonObject: AnyObject = NSJSONSerialization.JSONObjectWithData(receivedData, options: nil, error:&error) {
    if let dict = jsonObject as? NSDictionary {
        println(dict)
    } else {
        println("not a dictionary")
    }
} else {
    println("Could not parse JSON: \(error!)")
}

备注：

检查错误的正确方法是测试 return 值 ，而不是测试错误变量。
JSON 阅读选项 .AllowFragments 在这里没有帮助。设置这个选项只允许不是 NSArray 或 NSDictionary 实例的顶级对象，例如
```
{ "someString" }
```

您也可以在一行中完成，使用 可选类型转换 as?:

if let dict = NSJSONSerialization.JSONObjectWithData(receivedData, options: nil, error:nil) as? NSDictionary {
    println(dict)
} else {
    println("Could not read JSON dictionary")
}

缺点是在else情况下无法区分是否阅读 JSON 数据失败或者 JSON 不代表字典。

有关 Swift 3 的更新，请参阅。

Answer 2

更新 Swift 3

let jsonData = Data()
do {
    let jsonObject = try JSONSerialization.jsonObject(with: jsonData, options:JSONSerialization.ReadingOptions(rawValue: 0))
    guard let dictionary = jsonObject as? Dictionary<String, Any> else {
        print("Not a Dictionary")
        // put in function
        return
    }
    print("JSON Dictionary! \(dictionary)")
}
catch let error as NSError {
    print("Found an error - \(error)")
}

Swift 2

let JSONData = NSData()
do {
    let JSON = try NSJSONSerialization.JSONObjectWithData(JSONData, options:NSJSONReadingOptions(rawValue: 0))
    guard let JSONDictionary: NSDictionary = JSON as? NSDictionary else {
        print("Not a Dictionary")
        // put in function
        return
    }
    print("JSONDictionary! \(JSONDictionary)")
}
catch let JSONError as NSError {
    print("\(JSONError)")
}

Answer 3

这是一个 Swift 2 扩展，您可以使用它来反序列化一个 NSDictionary：

extension NSJSONSerialization{
    public class func dictionaryWithData(data: NSData, options opt: NSJSONReadingOptions) throws -> NSDictionary{
        guard let d: NSDictionary = try self.JSONObjectWithData(data, options:opt) as? NSDictionary else{
            throw NSError(domain: NSURLErrorDomain, code: NSURLErrorCannotParseResponse, userInfo: [NSLocalizedDescriptionKey : "not a dictionary"])
        }
        return d;
    }
}

抱歉，我不确定如何进行保护 return 以避免创建临时文件 'd'。

Answer 4

Swift 3 NSJSONSerialization 示例（从文件中读取 json）：

file data.json (example from here: http://json.org/example.html)

{
"glossary":{
"title":"example glossary",
"GlossDiv":{
    "title":"S",
    "GlossList":{
        "GlossEntry":{
            "ID":"SGML",
            "SortAs":"SGML",
            "GlossTerm":"Standard Generalized Markup Language",
            "Acronym":"SGML",
            "Abbrev":"ISO 8879:1986",
            "GlossDef":{
                "para":"A meta-markup language, used to create markup languages such as DocBook.",
                "GlossSeeAlso":[
                                "GML",
                                "XML"
                                ]
            },
            "GlossSee":"markup"
        }
    }
}
}
}

file JSONSerialization.swift

extension JSONSerialization {

enum Errors: Error {
    case NotDictionary
    case NotJSONFormat
}

public class func dictionary(data: Data, options opt: JSONSerialization.ReadingOptions) throws -> NSDictionary {
    do {
        let JSON = try JSONSerialization.jsonObject(with: data , options:opt)
        if let JSONDictionary = JSON as? NSDictionary {
            return JSONDictionary
        }
        throw Errors.NotDictionary
    }
    catch {
        throw Errors.NotJSONFormat
    }
}
}

用法

 func readJsonFromFile() {
    if let path = Bundle.main.path(forResource: "data", ofType: "json") {
        if let data = NSData(contentsOfFile: path) as? Data {

            do {
                let dict = try JSONSerialization.dictionary(data: data, options: .allowFragments)
                print(dict)
            } catch let error {
                print("\(error)")
            }

        }
    }
}

结果（日志截图）

Answer 5

Swift 3:

let jsonData = Data()
do {
    guard let parsedResult = try JSONSerialization.jsonObject(with: jsonData, options: .allowFragments) as? NSDictionary else {
        return
    }
    print("Parsed Result: \(parsedResult)")
} catch {
    print("Error: \(error.localizedDescription)")
}

Swift、NSJSONSerialization 和 NSError

Swift, NSJSONSerialization and NSError

swift

nsjsonserialization

nserror

用法

结果（日志截图）