Encode and decode swiftui MKPlacemark - swiftui

Question

I am new to SwiftUI and I am trying to encode and decode a MKPlacemark struct to json.
I have the struct defined as below. I am able to display the details in the app but I am not able to decode it.
import Foundation
import MapKit
import UIKit
struct Landmark {
let placemark: MKPlacemark
var id: UUID {
return UUID()
}
var name: String {
self.placemark.name ?? ""
}
var title: String {
self.placemark.title ?? ""
}
var coordinate: CLLocationCoordinate2D {
self.placemark.coordinate
}
}
I can search for placemarks like this:
import Foundation
import Combine
import MapKit
class SearchPlaces: NSObject, ObservableObject {
#Published var searchQuery = ""
#Published var landmarks: [Landmark] = [Landmark]()
#Published var items: [MapItem] = [MapItem]()
public func getNearByLandmarks() {
let request = MKLocalSearch.Request()
request.naturalLanguageQuery = searchQuery
let search = MKLocalSearch(request: request)
search.start { (response, error) in
if let response = response {
let mapItems = response.mapItems
self.landmarks = mapItems.map {
Landmark(placemark: $0.placemark)
}
Task {
await self.getData()
}
print("Lamdmarks \(self.landmarks)")
}
}
}
private func getData() async {
guard let landmark = try? JSONEncoder().encode(self.landmarks) else { return }
do {
let decodedLandmark = try JSONDecoder().decode(Landmark.self, from: landmark)
print("decodedLandmark \(decodedLandmark.id)")
} catch {
print("Error \(error.localizedDescription)")
}
}
}
But I get this error: Error
The data couldn’t be read because it isn’t in the correct format.
The placemark looks like this in xcode
Lamdmarks \[Landmark(placemark: La Hacienda Market, 249 Hillside Blvd, South San Francisco, CA 94080, United States # \<+37.66312925,-122.40844847\> +/- 0.00m, region CLCircularRegion (identifier:'\<+37.66307481,-122.40861130\> radius 141.17', center:\<+37.66307481,-122.40861130\>, radius:141.17m))
How do I decode a MKPlacemark to json when I don't know all of its keys.
I tried this
extension NSSecureCoding { func archived() throws -> Data { try NSKeyedArchiver.archivedData(withRootObject: self, requiringSecureCoding: false) } }
extension Data { func unarchived<T: NSSecureCoding>() throws -> T? { try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(self) as? T } }
extension Landmark: Codable {
func encode(to encoder: Encoder) throws {
var unkeyedContainer = encoder.unkeyedContainer()
try unkeyedContainer.encode(placemark.archived())
try unkeyedContainer.encode(id)
try unkeyedContainer.encode(name)
try unkeyedContainer.encode(title)
try unkeyedContainer.encode(coordinate)
}
public init(from decoder: Decoder) throws {
var container = try decoder.unkeyedContainer()
placemark = try container.decode(Data.self).unarchived()!
coordinate = try container.decode(CLLocationCoordinate2D.self, "coordinate")
id = try container.decode(UUID.self)
name = placemark.name ?? "no name"
title = placemark.title ?? "no title"
}
}

Answer 1

First of all never print(error.localizedDescription) in a Codable context. The generic error message is meaningless.
Always
print(error)
to get the real meaningful DecodingError.
Second of all don't try to adopt Codable by serializing each single property in classes which conform to NSSecureCoding. Take advantage of the built-in serialization and also of the PropertyWrapper pattern.
This PropertyWrapper converts/serializes MKPlacemark to Data and vice versa
#propertyWrapper
struct CodablePlacemark {
var wrappedValue: MKPlacemark
}
extension CodablePlacemark: Codable {
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
let data = try container.decode(Data.self)
guard let placemark = try NSKeyedUnarchiver.unarchivedObject(ofClass: MKPlacemark.self, from: data) else {
throw DecodingError.dataCorruptedError(
in: container,
debugDescription: "Invalid placemark"
)
}
wrappedValue = placemark
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
let data = try NSKeyedArchiver.archivedData(withRootObject: wrappedValue, requiringSecureCoding: true)
try container.encode(data)
}
}
In the Landmark struct adopt Codable and declare the placemark
struct Landmark: Codable {
#CodablePlacemark var placemark: MKPlacemark
}
But the property wrapper makes only sense if you encode the placemark.