Swift、NSJ系列化和NSError
问题是当存在不完整的数据时,Swift、NSJ系列化和NSError,swift,nsjsonserialization,nserror,Swift,Nsjsonserialization,Nserror,问题是当存在不完整的数据时,NSJSONSerialization.JSONObjectWithData会使应用程序崩溃,并在展开可选值时意外发现nil错误,而不是使用NSError变量通知我们。所以我们无法防止坠机 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: NSJSO
NSJSONSerialization.JSONObjectWithData
会使应用程序崩溃,并在展开可选值时意外发现nil错误,而不是使用NSError变量通知我们。所以我们无法防止坠机
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,我们还无法找到解决方法。问题在于,您在之前强制转换了JSON反序列化的结果 检查错误。如果JSON数据无效(例如不完整),则 返回
nil
和
NSJSONSerialization.JSONObjectWithData(...) as NSDictionary
将会崩溃
以下是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返回值,而不是 错误变量
- JSON读取选项
在这里没有帮助。设置此选项 例如,仅允许非.AllowFragments
或NSArray
实例的顶级对象NSDictionary
{ "someString" }
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,您无法区分是否正在阅读
JSON数据失败,或者JSON不代表字典
有关Swift 3的更新,请参阅。已更新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)")
}
以下是一个Swift 2扩展,可用于仅反序列化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,我不确定如何执行保护返回以避免创建临时“d”。Swift 3 NSJSONSerialization示例(从文件中读取json): 文件data.json(此处示例:) 文件JSONSerialization.swift 用法 结果(日志屏幕截图)
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)")
}
您解释为“这是一个正确检查错误条件的版本”的部分也没有捕获错误。它在以下行被压碎:AnyObject=NSJSONSerialization.JSONObjectWithData(receivedData,options:NSJSONReadingOptions.AllowFragments,error:&error)!我想说的是,如果收到的数据没有问题,我提交的这段代码和以前的代码都可以正常工作。@Hope:这不是我的建议。如果您使用
强制打开结果
那么您与NSDictionary的强制强制转换有相同的问题:如果结果为零,它将崩溃。让dataToUse:AnyObject?=NSJSONSerialization.JSONObjectWithData(receivedData,选项:NSJSONReadingOptions.AllowFragments,error:&error)似乎没有问题。所以我正在核对你们回答的问题。至少你对这个主题的理解更好。哎哟,和objc相比,swift的语法真的很糟糕。“let”、“do”、“try”、“guard”、“as?”、“catch”…这么多行话。如果你能捕捉到运行时异常(无法将其转换到NSDictionary),那就更好了,真不敢相信他们不得不添加一个全新的关键字guard来实现这一点。使用大写字母作为变量名是个坏主意,你会让人困惑。但同时,感谢您的回答。如果变量是首字母缩略词(例如JSON、URL等),我更喜欢将整个单词大写,否则它看起来很奇怪(JSON、URL)
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;
}
}
{
"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"
}
}
}
}
}
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
}
}
}
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)")
}
}
}
}
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)")
}