iOS 字典转json 需要注意

字典转json我们要注意NSJSONWritingOptions这个枚举类型：

typedef NS_OPTIONS(NSUInteger, NSJSONWritingOptions) {
    NSJSONWritingPrettyPrinted = (1UL << 0),

    /* Sorts dictionary keys for output using [NSLocale systemLocale]. Keys are compared using NSNumericSearch. The specific sorting method used is subject to change.
     */
    NSJSONWritingSortedKeys API_AVAILABLE(macos(10.13), ios(11.0), watchos(4.0), tvos(11.0)) = (1UL << 1),
    NSJSONWritingFragmentsAllowed = (1UL << 2),
    NSJSONWritingWithoutEscapingSlashes API_AVAILABLE(macos(10.15), ios(13.0), watchos(6.0), tvos(13.0)) = (1UL << 3),
} API_AVAILABLE(macos(10.7), ios(5.0), watchos(2.0), tvos(9.0));

• NSJSONWritingPrettyPrinted = (1UL << 0) //是将生成的json数据格式化输出，这样可读性高，不设置则输出的json字符串就是一整行。(自己原生打印输出，一般选用这个可读性比较高)；

• NSJSONWritingSortedKeys //输出的json字符串就是一整行（如果要往后台传或者字典转json然后加密，就不能格式化，会有换行符和空格）；这个枚举是iOS11后才出的，iOS11之前我们可以用kNilOptions来替代

• NSJSONWritingFragmentsAllowed 允许写入片段

• NSJSONWritingWithoutEscapingSlashes 不转义斜线