How to parse JSON in iOS App

by

I haven’t done JSON parsing myself in an iOS App, but you should be able to use a library like the json-framework. This library will allow you to easily parse JSON and generate json from dictionaries / arrays (that’s really all JSON is composed of).

SBJson docs:

JSON is mapped to Objective-C types in the following way:

  • null -> NSNull
  • string -> NSString
  • array -> NSMutableArray
  • object -> NSMutableDictionary
  • true -> NSNumber’s -numberWithBool:YES
  • false -> NSNumber’s -numberWithBool:NO
  • integer up to 19 digits -> NSNumber’s -numberWithLongLong:
  • all other numbers -> NSDecimalNumber

Since Objective-C doesn’t have a dedicated class for boolean values,
these turns into NSNumber instances. However, since these are
initialised with the -initWithBool: method they round-trip back to JSON
properly. In other words, they won’t silently suddenly become 0 or 1;
they’ll be represented as ‘true’ and ‘false’ again.

As an optimisation integers up to 19 digits in length (the max length
for signed long long integers) turn into NSNumber instances, while
complex ones turn into NSDecimalNumber instances. We can thus avoid any
loss of precision as JSON allows ridiculously large numbers.

@page objc2json Objective-C to JSON

Objective-C types are mapped to JSON types in the following way:

  • NSNull -> null
  • NSString -> string
  • NSArray -> array
  • NSDictionary -> object
  • NSNumber’s -initWithBool:YES -> true
  • NSNumber’s -initWithBool:NO -> false
  • NSNumber -> number

@note In JSON the keys of an object must be strings. NSDictionary
keys need not be, but attempting to convert an NSDictionary with
non-string keys into JSON will throw an exception.

NSNumber instances created with the -numberWithBool: method are
converted into the JSON boolean “true” and “false” values, and vice
versa. Any other NSNumber instances are converted to a JSON number the
way you would expect.

Tutorials

Are there any tutorials? Yes! These are all tutorials provided by
third-party people:

JSON Framework for iPhone – a Flickr tutorial in three parts by John
Muchow. JSON Over HTTP On The iPhone – by Dan Grigsby. AS3 to Cocoa touch: JSON by Andy Jacobs.

There are other libraries you can check out as well like TouchJSON, JSONKit, Yet Another JSON Library

More Related Contents:

  1. how yo access item key in swift 4
  2. Parse JSON with Objective-C
  3. Split a String into an array in Swift?
  4. Generate JSON string from NSDictionary in iOS
  5. Convert Swift string to array
  6. Convert array to JSON string in swift
  7. Parsing nested Array of Dictionaries using Object Mapper
  8. How to implement the Hashable Protocol in Swift for an Int array (a custom string struct)
  9. JSON parsing swift, array has no value outside NSURLSession
  10. Convert string to mutable data – objective c [duplicate]
  11. How can I convert string date to NSDate?
  12. Get the length of a String
  13. Find out if Character in String is emoji?
  14. How to save Array to CoreData?
  15. Convert JSON String to JSON Object c#
  16. Converting escaped UTF8 characters back to their original form
  17. Foreign key relationship mapping with RestKit
  18. Can JSON numbers be quoted?
  19. Best way to parse URL string to get values for keys?
  20. Sort Array of Dictionaries by Key Value
  21. Convert an iOS objective c object to a JSON string
  22. Implementing Google custom search API in iOS
  23. How to split filename from file extension in Swift?
  24. How can I combine two Dictionary instances in Swift?
  25. How to remove special characters from string in Swift 2?
  26. POST request using application/x-www-form-urlencoded
  27. Swift String escaping when serializing to JSON using Codable
  28. How can you deserialize an escaped JSON string with NSJSONSerialization?
  29. Swift JSON error : Could not cast value of type ‘__NSDictionaryM’ to ‘NSArray’
  30. Find an item and change value in custom object array – Swift

Leave a Comment