1. NSDictionary->JSON
NSDictionary *jsonDic = @{};
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:jsonDic options:0 error:nil]; // 如果不想要 JSON 字符串里带空格或换行等 options 传 0
NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
2. JSON->NSDictionary
NSString *jsonString = @"";
NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
NSDictionary *jsonDic = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:nil];
3. NSJSONReadingOptions 枚举说明
NSJSONReadingMutableContainers // Specifies that arrays and dictionaries are created as mutable objects.
NSJSONReadingMutableLeaves // Specifies that leaf strings in the JSON object graph are created as instances of NSMutableString.
NSJSONReadingAllowFragments // Specifies that the parser should allow top-level objects that are not an instance of NSArray or NSDictionary.
