Swift: How to Convert an Array to JSON

In Swift, a JSON object is an instance of the Data class, which is a binary representation of the JSON string, and arrays are one of the most used data structures. This succinct, example-based article will show you a couple of different ways to convert a given array to JSON.

Using JSONEncoder.encode() method

The JSONEncoder.encode(_:) and String(data:encoding:) of the Foundation framework can convert an array that contains instances of a custom type that conforms to the Codable protocol to a JSON data object and then to a JSON string, respectively.

Example:

import Foundation

// Define a custom type that conforms to Codable protocol
struct Person: Codable {
    var name: String
    var age: Int
}

// Create an array of Person objects
let array = [
    Person(name: "Red Wolf", age: 99),
    Person(name: "Ronaldo", age: 39),
    Person(name: "Thanos", age: 200),
]

// Create an instance of JSONEncoder
let encoder = JSONEncoder()

// Convert array to JSON data
let data = try encoder.encode(array)

// Convert JSON data to JSON string
let string: String? = String(data: data, encoding: .utf8)
print(string!)

Output:

[{"name":"Red Wolf","age":99},{"name":"Ronaldo","age":39},{"name":"Thanos","age":200}]

Using JSONSerialization.data() method

An alternative solution is to use the built-in methodJSONSerialization.data(withJSONObject:options:) of the Foundation framework. It can convert an array that contains only JSON-encodable values (such as string, number, dictionary, array, or nil) to a JSON data object. You can turn this object into a JSON string by using the String(data:encoding:) method.

You should use the try/catch syntax to handle any potential errors that may occur during the conversion process as shown in the example below:

import Foundation

let myArray = ["Sling Academy", "Swift", "iOS", "Example"]

do {
    // Convert array to JSON data
    let data = try JSONSerialization.data(
        withJSONObject: myArray,
        options: []
    )

    // Convert JSON data to JSON string
    let jsonString: String? = String(data: data, encoding: .utf8)

    // Print JSON string
    print(jsonString ?? "JSON string is nil")
} catch {
    // Handle error
    print(error.localizedDescription)
}

Output:

["Sling Academy","Swift","iOS","Example"]