# JSONSerialization.ReadingOptions

## 介绍 ReadingOptions

这三个 case

* mutableContainers 得到一个可变对象
* mutableLeaves JSON 的叶子节点如果是 String 类型，会被创建成可变类型的 String
* fragmentsAllowed 除了 Map 和 Arrary  这两个数据结构可以作为 JSON 顶层，还允许其他类型作为顶层，比如 string，number，null，bool 。

```swift
    @available(iOS 5.0, *)
    public struct ReadingOptions : OptionSet {

        public init(rawValue: UInt)


        public static var mutableContainers: JSONSerialization.ReadingOptions { get }

        public static var mutableLeaves: JSONSerialization.ReadingOptions { get }

        public static var fragmentsAllowed: JSONSerialization.ReadingOptions { get }

        @available(iOS, introduced: 5.0, deprecated: 100000, renamed: "JSONSerialization.ReadingOptions.fragmentsAllowed")
        public static var allowFragments: JSONSerialization.ReadingOptions { get }
    }
```

## 验证

#### 一，mutableContainers

> 验证所有类型后，得到结论，Map 和 Arrary 类型转换后可以得到可变类型，其他类型 比如，单独的 string，单独的 number 都不可以。

1.得到可变对象 `__NSDictionaryM`

```swift
let str = "{\"name\":\"henry\"}"
let data = str.data(using: .utf8)
let options: JSONSerialization.ReadingOptions = [.mutableContainers]
let json = try! JSONSerialization.jsonObject(with: data!, options: options)
print(type(of: json))
print(json)

// 输出
__NSDictionaryM
{
    name = henry;
}
```

2.得到不可变对象 `__NSSingleEntryDictionaryI`

```swift
let str = "{\"name\":\"henry\"}"
let data = str.data(using: .utf8)
let options: JSONSerialization.ReadingOptions = []
let json = try! JSONSerialization.jsonObject(with: data!, options: options)
print(type(of: json))
print(json)

// 输出
__NSSingleEntryDictionaryI
{
    name = henry;
}
```

#### 二，allowFragments

> 验证后，得到结论是： bool,number,null,string,map,arrary 都可以做 JSON 的最外层结构。

1. bool 类型

```swift
let str = "true"
let data = str.data(using: .utf8)
let options: JSONSerialization.ReadingOptions = [.mutableContainers,.allowFragments]
let json = try! JSONSerialization.jsonObject(with: data!, options: options)
print(type(of: json))
print(json)

//输出
__NSCFBoolean
1
```

1. number 类型

```swift
let str = "1.2"
let data = str.data(using: .utf8)
let options: JSONSerialization.ReadingOptions = [.mutableContainers,.allowFragments]
let json = try! JSONSerialization.jsonObject(with: data!, options: options)
print(type(of: json))
print(json)

//输出
NSDecimalNumber
1.2
```

1. string 类型

```swift
let str = "\"1.2\""
let data = str.data(using: .utf8)
let options: JSONSerialization.ReadingOptions = [.mutableContainers,.allowFragments]
let json = try! JSONSerialization.jsonObject(with: data!, options: options)
print(type(of: json))
print(json)

//输出
NSTaggedPointerString
1.2
```

1. null 类型

```swift
let str = "null"
let data = str.data(using: .utf8)
let options: JSONSerialization.ReadingOptions = [.mutableContainers,.allowFragments]
let json = try! JSONSerialization.jsonObject(with: data!, options: options)
print(type(of: json))
print(json)

//输出
NSNull
<null>
```

1. arrary 类型

```swift
let str = "[\"1\"]"
let data = str.data(using: .utf8)
let options: JSONSerialization.ReadingOptions = [.mutableContainers,.allowFragments]
let json = try! JSONSerialization.jsonObject(with: data!, options: options)
print(type(of: json))
print(json)

//输出
__NSArrayM
(
    1
)
```

1. object 类型

```swift
let str = "{\"1\":\"2\"}"
let data = str.data(using: .utf8)
let options: JSONSerialization.ReadingOptions = [.mutableContainers,.allowFragments]
let json = try! JSONSerialization.jsonObject(with: data!, options: options)
print(type(of: json))
print(json)

//输出
__NSDictionaryM
{
    1 = 2;
}
```

#### 三，mutableLeaves

苹果官方文档描述这个 Case: Specifies that leaf strings in the JSON object graph are created as instances of `NSMutableString`.

翻译过来就是： JSON 的叶子数据，如果是 string 类型，转换过来会被转换成 NSMutableString，**但是**，我不论是在 swift 还是 oc 都是不行，确实大家也都遇到了。 比如 <https://link.jianshu.com/?t=http://stackoverflow.com/questions/19345864/nsjsonreadingmutableleaves-option-is-not-working>

做个实验：

```swift
let str = "{\"1\":\"2\"}"
let data = str.data(using: .utf8)
let options: JSONSerialization.ReadingOptions = [.mutableContainers,.allowFragments,.mutableLeaves]
let json = try! JSONSerialization.jsonObject(with: data!, options: options) as! [String: Any]
print(type(of: json["1"]!))
print(json)

//输出
NSTaggedPointerString
["1": 2]
```

确实没有像文档说的那样会创建一个 NSMutableString，不过对我们使用 swift 的童鞋木有啥影响。


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