NEW! Check out my latest book, Testing Swift! >>

How to parse JSON using JSONSerialization

Paul Hudson       @twostraws

The built-in iOS way of parsing JSON is called JSONSerialization and it can convert a JSON string into a collection of dictionaries, arrays, strings and numbers in just a few lines of code.

In the example below, I create a dummy piece of JSON that contains three names in an array cunningly called "names". This then gets sent to JSONSerialization (by converting it into a Data object, which is how JSONSerialization likes to receive its content), and I conditionally pull out and print the names array:

let str = "{\"names\": [\"Bob\", \"Tim\", \"Tina\"]}"
let data = str.data(using: String.Encoding.utf8, allowLossyConversion: false)!

do {
    let json = try JSONSerialization.jsonObject(with: data, options: []) as! [String: AnyObject]
    if let names = json["names"] as? [String] {
        print(names)
    }
} catch let error as NSError {
    print("Failed to load: \(error.localizedDescription)")
}

There are a couple of things that might confuse you there. First, because parsing JSON will fail if the JSON isn't valid, you need to use try/catch and have some sort of error handling. Second, you need to force typecast the JSON to be a dictionary of type [String: AnyObject] so that you can start working with your JSON values. Third, you don't know for sure that any values exist inside the JSON, so you need to conditionally check for and unwrap the names value.

Available from iOS 5.0 – see Hacking with Swift tutorial 7

Did this solution work for you? Please pass it on!

Other people are reading…

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.

Learn Swift faster!

Take your Swift learning to the next level: buy the Hacking with Swift e-book and get bonus material to help you learn faster!

MASTER SWIFT NOW
Buy Testing Swift Buy Practical iOS 12 Buy Pro Swift Buy Swift Design Patterns Buy Swift Coding Challenges Buy Server-Side Swift (Vapor Edition) Buy Server-Side Swift (Kitura Edition) Buy Hacking with macOS Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with Swift Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let me know!

Average rating: 2.3/5

Click here to visit the Hacking with Swift store >>