iOS开发——网络编程Swift篇&（八）SwiftyJSON详解
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时间：2015年06月11日
SwiftyJSON详解
最近看了一些网络请求的例子，发现Swift在解析JSON数据时特别别扭，总是要写一大堆的downcast(as?)和可选(Optional)，看?号都看花了。随后发现了这个库SwiftyJSON，问题迎刃而解，灰常优雅和Swifty！
简单介绍下这个库（内容译自SwiftyJSON的README）：
为什么典型的在Swift中处理JSON的方法不好？
Swift语言是一种严格的类型安全语言，它要求我们显示的设置类型，并帮助我们写出更少bug的代码。但是当处理JSON这种天生就是隐式类型的数据结构，就非常麻烦了。
拿Twitter中timeline API返回的数据为例：
1 [ 2 { 3 ...... 4 "text": "just another test", 5 ...... 6 "user": { 7 "name": "OAuth Dancer", 8 "favourites_count": 7, 9 "entities": { 10 "url": { 11 "urls": [ 12 { 13 "expanded_url": null, 14 "url": "http://bit.ly/oauth-dancer", 15 "indices": [ 16 0, 17 26 18 ], 19 "display_url": null 20 } 21 ] 22 } 23 ...... 24 }, 25 "in_reply_to_screen_name": null, 26 }, 27 ......]
Swift中的解析代码会是这样：
1 let jsonObject : AnyObject! = NSJSONSerialization.JSONObjectWithData(dataFromTwitter, options: NSJSONReadingOptions.MutableContainers, error: nil) 2 if let statusesArray = jsonObject as? NSArray{ 3 if let aStatus = statusesArray[0] as? NSDictionary{ 4 if let user = aStatus["user"] as? NSDictionary{ 5 if let userName = user["name"] as? NSDictionary{ 6 //终于我们得到了`name` 7 8 } 9 } 10 } 11 }
不好吧。就算是换成可选链式调用，也还是一团糟：
1 let jsonObject : AnyObject! = NSJSONSerialization.JSONObjectWithData(dataFromTwitter, options: NSJSONReadingOptions.MutableContainers, error: nil) 2 if let userName = (((jsonObject as? NSArray)?[0] as? NSDictionary)?["user"] as? NSDictionary)?["name"]{ 3 //上面这一堆是个啥？？ 4 }
使用SwiftyJSON
你只要这样做就行了：
let json = JSONValue(dataFromNetworking)
if let userName = json[0]["user"]["name"].string{
//恩~ `name`到手，就这么简单
}
你不需要考虑可选类型的拆包和是否能拆包的判断，这些都自动完成了：
1 let json = JSONValue(dataFromNetworking) 2 if let userName = json[999999]["wrong_key"]["wrong_name"].string{ 3 //冷静，嘿嘿~ 调用不存在的["wrong_key]也不会crash滴， .string最终能安全的返回一个字符串或`nil` 4 } 5 6 let json = JSONValue(jsonObject) 7 switch json["user_id"]{ 8 case .JString(let stringValue): 9 let id = stringValue.toInt() 10 case .JNumber(let doubleValue): 11 let id = Int(doubleValue) 12 default: 13 println("ooops!!! JSON Data is Unexpected or Broken")
后记：SwiftyJSON是怎么做到的？
看到这个库之后，一方面很爽终于有合适的处理JSON的方法了；另一方面心里其实很好奇它是怎么做到的？
通过看源代码，才了解到它是创建了一个JSONValue枚举，这个枚举中有一个JInvalid类型。当使用json字符串来构造JSONValue对象时，如果无法构建成功，就会返回这个JInvalid枚举对象，然后对这个JInvalid枚举对象继续处理，会继续返回JInvalid。直到对其调用string, number, bool之类来获取Swift中的数据类型值时，才会返回nil。
这套机制是类似于Optional<T>可选类型的，但是不同的是，Optional中对nil调用方法会crash，但JSONValue中对JInvalid调用方法不会crash，而是继续返回JInvalid。这样使用时就不用写一堆?号啦，反正不会出错滴。
同时，它给JSONValue枚举还创建了其它json中使用到的各种类型JNumber, JString, JBool，它们能通过构造器将原始值包装起来，然后最后通过对应的number，string，bool等属性方法来拆包，得到原始值。
推荐大家也读读这个库的源代码，其对enum的使用灰常巧妙！
json-swift 和 SwiftyJSON 的比较
最近微博上 @SwiftLanguage 让我对这两个库做个简单比较，所以就有了下文：
json-swift和SwiftyJSON都使用了一个自定义的枚举类型来描述JSON数据；通过重载实现了类似Array和Dictionary的下标操作；并可以将NSData类型的json实例转换成其对应的枚举类型的实例。
它们都解决了原来访问JSON类型数据时，必须手动downcast的繁琐操作，如原来要json[“blogs”]? as? Array，现在json[“blogs”]?即可。SwiftyJSON更进一步，连?也可以省掉，使用上更接近Objective-C风格；json-swift保留了?，跟Swift整体风格一致，此外还提供了直接从字面值实例化的便捷操作。
关于用不用?，我个人倾向于SwiftyJSON的做法。其最大优势是可以省写很多?号，无论写程序还是看程序都变得更简单直观；同时由于json结构中数据类型本身就是动态的，如果把每次取值当做一次操作，那么取值的过程不那么type-safe我认为可以接受，只要最终能保证取值结果跟Swift兼容（可选类型）。
if you love it, please page to :https://github.com/SwiftyJSON/SwiftyJSON
1 Why is the typical JSON handling in Swift NOT good? 2 3 Swift is very strict about types. But although explicit typing is good for saving us from mistakes, it becomes painful when dealing with JSON and other areas that are, by nature, implicit about types. 4 5 Take the Twitter API for example. Say we want to retrieve a user‘s "name" value of some tweet in Swift (according to Twitter‘s API https://dev.twitter.com/docs/api/1.1/get/statuses/home_timeline). 6 7 The code would look like this: 8 9 let JSONObject: AnyObject? = NSJSONSerialization.JSONObjectWithData(data, options: nil, error: nil) 10 11 if let statusesArray = JSONObject as? [AnyObject], 12 let status = statusesArray[0] as? [String: AnyObject], 13 let user = status["user"] as? [String: AnyObject], 14 let username = user["name"] as? String { 15 // Finally we got the username 16 } 17 18 It‘s not good. 19 20 Even if we use optional chaining, it would be messy: 21 22 let JSONObject: AnyObject? = NSJSONSerialization.JSONObjectWithData(data, options: nil, error: nil) 23 24 if let username = (((JSONObject as? [AnyObject])?[0] as? [String: AnyObject])?["user"] as? [String: AnyObject])?["name"] as? String { 25 // What a disaster 26 } 27 28 An unreadable mess--for something that should really be simple! 29 30 With SwiftyJSON all you have to do is: 31 32 let json = JSON(data: dataFromNetworking) 33 if let userName = json[0]["user"]["name"].string{ 34 //Now you got your value 35 } 36 37 And don‘t worry about the Optional Wrapping thing. It‘s done for you automatically. 38 39 let json = JSON(data: dataFromNetworking) 40 if let userName = json[999999]["wrong_key"]["wrong_name"].string{ 41 //Calm down, take it easy, the ".string" property still produces the correct Optional String type with safety 42 } else { 43 //Print the error 44 println(json[999999]["wrong_key"]["wrong_name"]) 45 } 46 47 Requirements 48 49 iOS 7.0+ / Mac OS X 10.9+ 50 Xcode 6.1 51 52 Integration 53 CocoaPods (iOS 8+, OS X 10.9+) 54 55 You can use Cocoapods to install SwiftyJSONby adding it to your Podfile: 56 57 platform :ios, ‘8.0‘ 58 use_frameworks! 59 60 target ‘MyApp‘ do 61 pod ‘SwiftyJSON‘, ‘~> 2.2.0‘ 62 end 63 64 Note that it needs you to install CocoaPods 36 version, and requires your iOS deploy target >= 8.0: 65 Carthage (iOS 8+, OS X 10.9+) 66 67 You can use Carthage to install SwiftyJSON by adding it to your Cartfile: 68 69 github "SwiftyJSON/SwiftyJSON" >= 2.2.0 70 71 Manually (iOS 7+, OS X 10.9+) 72 73 To use this library in your project manually you may: 74 75 for Projects, just drag SwiftyJSON.swift to the project tree 76 for Workspaces, include the whole SwiftyJSON.xcodeproj 77 78 Usage 79 Initialization 80 81 import SwiftyJSON 82 83 let json = JSON(data: dataFromNetworking) 84 85 let json = JSON(jsonObject) 86 87 if let dataFromString = jsonString.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false) { 88 let json = JSON(data: dataFromString) 89 } 90 91 Subscript 92 93 //Getting a double from a JSON Array 94 let name = json[0].double 95 96 //Getting a string from a JSON Dictionary 97 let name = json["name"].stringValue 98 99 //Getting a string using a path to the element 100 let path = [1,"list",2,"name"] 101 let name = json[path].string 102 //Just the same 103 let name = json[1]["list"][2]["name"].string 104 //Alternatively 105 let name = json[1,"list",2,"name"].string 106 107 //With a hard way 108 let name = json[].string 109 110 //With a custom way 111 let keys:[SubscriptType] = [1,"list",2,"name"] 112 let name = json[keys].string 113 114 Loop 115 116 //If json is .Dictionary 117 for (key: String, subJson: JSON) in json { 118 //Do something you want 119 } 120 121 The first element is always a String, even if the JSON is an Array 122 123 //If json is .Array 124 //The `index` is 0..<json.count‘s string value 125 for (index: String, subJson: JSON) in json { 126 //Do something you want 127 } 128 129 Error 130 131 Use a subscript to get/set a value in an Array or Dictionary 132 133 If the json is: 134 135 an array, the app may crash with "index out-of-bounds." 136 a dictionary, it will get nil without a reason. 137 not an array or a dictionary, the app may crash with an "unrecognised selector" exception. 138 139 It will never happen in SwiftyJSON. 140 141 let json = JSON(["name", "age"]) 142 if let name = json[999].string { 143 //Do something you want 144 } else { 145 println(json[999].error) // "Array[999] is out of bounds" 146 } 147 148 let json = JSON(["name":"Jack", "age": 25]) 149 if let name = json["address"].string { 150 //Do something you want 151 } else { 152 println(json["address"].error) // "Dictionary["address"] does not exist" 153 } 154 155 let json = JSON(12345) 156 if let age = json[0].string { 157 //Do something you want 158 } else { 159 println(json[0]) // "Array[0] failure, It is not an array" 160 println(json[0].error) // "Array[0] failure, It is not an array" 161 } 162 163 if let name = json["name"].string { 164 //Do something you want 165 } else { 166 println(json["name"]) // "Dictionary[\"name"] failure, It is not an dictionary" 167 println(json["name"].error) // "Dictionary[\"name"] failure, It is not an dictionary" 168 } 169 170 Optional getter 171 172 //NSNumber 173 if let id = json["user"]["favourites_count"].number { 174 //Do something you want 175 } else { 176 //Print the error 177 println(json["user"]["favourites_count"].error) 178 } 179 180 //String 181 if let id = json["user"]["name"].string { 182 //Do something you want 183 } else { 184 //Print the error 185 println(json["user"]["name"]) 186 } 187 188 //Bool 189 if let id = json["user"]["is_translator"].bool { 190 //Do something you want 191 } else { 192 //Print the error 193 println(json["user"]["is_translator"]) 194 } 195 196 //Int 197 if let id = json["user"]["id"].int { 198 //Do something you want 199 } else { 200 //Print the error 201 println(json["user"]["id"]) 202 } 203 ... 204 205 Non-optional getter 206 207 Non-optional getter is named xxxValue 208 209 //If not a Number or nil, return 0 210 let id: Int = json["id"].intValue 211 212 //If not a String or nil, return "" 213 let name: String = json["name"].stringValue 214 215 //If not a Array or nil, return [] 216 let list: Array<JSON> = json["list"].arrayValue 217 218 //If not a Dictionary or nil, return [:] 219 let user: Dictionary<String, JSON> = json["user"].dictionaryValue 220 221 Setter 222 223 json["name"] = JSON("new-name") 224 json[0] = JSON(1) 225 226 json["id"].int = 1234567890 227 json["coordinate"].double = 8766.766 228 json["name"].string = "Jack" 229 json.arrayObject = [1,2,3,4] 230 json.dictionary = ["name":"Jack", "age":25] 231 232 Raw object 233 234 let jsonObject: AnyObject = json.object 235 236 if let jsonObject: AnyObject = json.rawValue 237 238 //convert the JSON to raw NSData 239 if let data = json.rawData() { 240 //Do something you want 241 } 242 243 //convert the JSON to a raw String 244 if let string = json.rawString() { 245 //Do something you want 246 } 247 248 Literal convertibles 249 250 For more info about literal convertibles: Swift Literal Convertibles 251 252 //StringLiteralConvertible 253 let json: JSON = "I‘m a json" 254 255 //IntegerLiteralConvertible 256 let json: JSON = 12345 257 258 //BooleanLiteralConvertible 259 let json: JSON = true 260 261 //FloatLiteralConvertible 262 let json: JSON = 2.8765 263 264 //DictionaryLiteralConvertible 265 let json: JSON = ["I":"am", "a":"json"] 266 267 //ArrayLiteralConvertible 268 let json: JSON = ["I", "am", "a", "json"] 269 270 //NilLiteralConvertible 271 let json: JSON = nil 272 273 //With subscript in array 274 var json: JSON = [1,2,3] 275 json[0] = 100 276 json[1] = 200 277 json[2] = 300 278 json[999] = 300 //Don‘t worry, nothing will happen 279 280 //With subscript in dictionary 281 var json: JSON = ["name": "Jack", "age": 25] 282 json["name"] = "Mike" 283 json["age"] = "25" //It‘s OK to set String 284 json["address"] = "L.A." // Add the "address": "L.A." in json 285 286 //Array & Dictionary 287 var json: JSON = ["name": "Jack", "age": 25, "list": ["a", "b", "c", ["what": "this"]]] 288 json["list"][3]["what"] = "that" 289 json["list",3,"what"] = "that" 290 let path = ["list",3,"what"] 291 json[path] = "that" 292 293 Work with Alamofire 294 295 SwiftyJSON nicely wraps the result of the Alamofire JSON response handler: 296 297 Alamofire.request(.GET, url, parameters: parameters) 298 .responseJSON { (req, res, json, error) in 299 if(error != nil) { 300 NSLog("Error: \(error)") 301 println(req) 302 println(res) 303 } 304 else { 305 NSLog("Success: \(url)") 306 var json = JSON(json!) 307 } 308 }
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