JSON is a standard of data interchange that can be very handy for getting information into and out of an app. By Parsing in JSON from the outside world an app can dynamically display new information such as the latest weather, sports scores or travel information. There are many exciting API JSON feeds out there that make it possible to build an app capable of accessing information in real time over a network connect.

Besides 3rd party APIs, JSON is a powerful tool for piping in your own custom data, even after a user has downloaded the app.  A simple example might be in an app for Chuck Norris facts. Instead of shipping the app with 1000 round-house related tidbits the developer could store an array of facts in JSON format on an Amazon Web Services S3 bucket. The app can then be updated with new facts dynamically over a network without users having to do a version update from the store.

Faster and less verbose than XML JSON is also considered to be much more “human-readable”.  So congratulations if you are indeed a human!

This post will cover how to create a text file containing JSON using Swift.

Chuck Norris’ methods only accept 1 argument: hisFist. They all return nil

Jovial Sausages On Neptune

…is not what JSON stands for. Why would you say that? JavaScript Object Notation is in fact the correct acronym. Although JSON has Javascript in the name it’s actually language independent and is in essence a text format of keys and values. Let’s look at how these components can be built in Swift.

Dictionaries

Dictionaries are a collection type where data is stored as pairs of keys and values. The keys must all be of the same type, so they could be all String or all Int for example. However the associated values can be of different types.

Here are the data types available for JSON serialization.

• Dictionary
• Array
• String
• Int, Double, Float
• Boolean

// Create a new dictionary 

var villain1: [String : AnyObject] = ["name" : "Jason Voorhees",
                                   "born" : 1945,
                                   "murder count" : 127,
                                   "likes" : ["hockey", "occasional Fridays"],
                                   "dislikes" : "water sports"]

// Some examples of working with a dictionary 

villain1["name"]   // "Jason Voorhees"

villain1.count     // 5   (number of key value pairs in dictionary)

villain1.updateValue("traveling during Thanksgiving", forKey: "dislikes")

Let’s create two more dictionaries of villainous information and add these to an array. The array will now be an array of dictionaries (with the format String : AnyObject).

// Two more dictionaries

let villain2: [String : AnyObject] = ["name" : "Freddie Krueger",
                                   "born" : 1942,
                                   "murder count" : 35,
                                   "likes" : ["bed time", "knitwear"],
                                   "dislikes" : "barbecues"]

let villain3: [String : AnyObject] = ["name" : "Michael Myers",
                                   "born" : 1978,
                                   "murder count" : 94,
                                   "likes" : ["leaves changing color in the fall", "Austin Powers Movies"],
                                   "dislikes" : "Jamie Lee Curtis"]

// Add these dictionaries to an array of villains

var villainArray: [[String : AnyObject]] = [villain1, villain2, villain3]

To Chuck Norris a retina display looks like an Atari 2600

To convert the array into JSON data Apple provides the NSJSONSerialization class. The option NSJSONWritingOptions.PrettyPrinted simply formats the JSON with carriage returns so that it isn’t one giant long string. Once an NSData object is created it’s convert into a string that’s printed to the console. It’s then possible to copy and paste the string into a text file with the extension “.json”. The JSON file could then be uploaded to an Amazon S3 bucket.

var jsonData: NSData!

do {
    jsonData = try NSJSONSerialization.dataWithJSONObject(villainArray, options: .PrettyPrinted)
    
} catch let error as NSError {
    print(error)
}

let jsonString = String(data: jsonData, encoding: NSUTF8StringEncoding)!
print(jsonString)

The print out would look like this:

Chuck Norris doesn’t need the compiler. Swift turns itself into machine code purely out of fear.

This whole process could be combined into a single function (existing in a separate Swift file in the project). As an alternative to manually going in and altering a text file containing the JSON the dictionaries and array within this function could be modified, re-output to the console and used to update the text file.  A template for this would look like so:

func makeJSONOutput() {
    
    var jsonArray: [[String:String]] = []
    
    var jsonData: NSData!
    
    let dict1: [String:String] = ["key1" : "value1",
                                  "key2" : "value2"]
    
    jsonArray.append(dict1)
    
    let dict2: [String:String] = ["key1" : "value1",
                                  "key2" : "value2"]
    
    jsonArray.append(dict2)
    
    // add more dictionaries here
    
    
    do {
        jsonData = try NSJSONSerialization.dataWithJSONObject(jsonArray, options: .PrettyPrinted)
        
    } catch let error as NSError {
        print(error)
    }
    
    let jsonString = String(data: jsonData, encoding: NSUTF8StringEncoding)!
    print(jsonString)
    
}

makeJSONOutput()

Download the code examples from GitHub here