Simple Swift UI Json App - decoding issue - json

Question

I am trying to create a simple Swift UI app to download some json from the web and then display it on the screen.
I have 2 calls - a general lookup call for an array of items which are displayed in a View. I then have a detailed lookup, based upon the id chosen by the user in the first View which is then displayed in a second View.
I am able to access the parsed data via 2 #Published properties in my NetworkController class which I access from my Views, using: .onAppear to trigger the calls when the user arrives at each view.
My first call is working and I am able to display a list of items and then select them and read their id, which I then use for the second call.
The second call is causing me problems, though and I am getting an error decoding.
As there is quite a bit of code I’ve created a single Playground which includes some sample Json and the functions which I use, which is producing the error.
I am doing both calls using the same procedure - e.g. a number of function - which I have applied from another app which does a similar thing. My guess is that the error is because I have misunderstood some part of how these work. Because of this, I’ve commented what I think they are doing, to give an idea of what I am trying to achieve. Because the first call is working I am thinking that my understanding is partially correct, but I must be missing something.
The element that differs between the first data call and the second one is that the first one only requires a single struct to parse all the data whereas the second call uses a nested struct. I am thinking that I may need to adjust something to accomodate this - I am using the outermost struct - but I’m not clear exactly what I need to do.
If anyone has any suggestions I would be very grateful.
######################################################
# PLAYGROUND
######################################################
import Cocoa
var itemDetailed: ItemCodable? = nil
var item: Item
// ################################################################
// EXAMPLE JSON DATA
// ################################################################
let data = """
{
"item": {
"general": {
"id": 11,
"name": "app_install",
"enabled": true,
"trigger": "CHECKIN",
"trigger_checkin": true,
"trigger_enrollment_complete": false,
"trigger_login": false,
"trigger_network_state_changed": false,
"trigger_startup": false,
"trigger_other": "",
"frequency": "Ongoing",
"retry_event": "none",
"retry_attempts": -1,
"notify_on_each_failed_retry": false,
"location_user_only": false,
"target_drive": "/",
"offline": false,
"category": {
"id": 3,
"name": "Apps"
},
"date_time_limitations": {
"activation_date": "",
"activation_date_epoch": 0,
"activation_date_utc": "",
"expiration_date": "",
"expiration_date_epoch": 0,
"expiration_date_utc": "",
"no_execute_on": {},
"no_execute_start": "",
"no_execute_end": ""
},
"network_limitations": {
"minimum_network_connection": "No Minimum",
"any_ip_address": true,
"network_segments": []
},
"override_default_settings": {
"target_drive": "default",
"distribution_point": "",
"force_afp_smb": false,
"sus": "default"
},
"network_requirements": "Any",
"site": {
"id": -1,
"name": "None"
}
},
"scope": {
"all_computers": false,
"computers": [],
"computer_groups": [
{
"id": 1,
"name": "All Managed Clients"
}
],
"buildings": [],
"departments": [],
"limit_to_users": {
"user_groups": []
},
"limitations": {
"users": [],
"user_groups": [],
"network_segments": [],
"ibeacons": []
},
"exclusions": {
"computers": [],
"computer_groups": [
{
"id": 9,
"name": "app_installed_testutil"
}
],
"buildings": [],
"departments": [],
"users": [],
"user_groups": [],
"network_segments": [],
"ibeacons": []
}
},
"self_service": {
"use_for_self_service": false,
"self_service_display_name": "",
"install_button_text": "Install",
"reinstall_button_text": "Reinstall",
"self_service_description": "",
"force_users_to_view_description": false,
"self_service_icon": {},
"feature_on_main_page": false,
"self_service_categories": [],
"notification": "Self Service",
"notification_subject": "app_install",
"notification_message": ""
},
"package_configuration": {
"packages": [
{
"id": 3,
"name": "testutil_2.0.5.psr",
"action": "Install",
"fut": false,
"feu": false
}
]
},
"scripts": [],
"printers": [
""
],
"dock_items": [],
"account_maintenance": {
"accounts": [],
"directory_bindings": [],
"management_account": {
"action": "doNotChange"
},
"open_firmware_efi_password": {
"of_mode": "none",
"of_password_sha256": "xxxxxyyyyyyyyyzzzzzzzzaaaabbbbbbccccccc"
}
},
"reboot": {
"message": "This computer will restart in 5 minutes.",
"startup_disk": "Current Startup Disk",
"specify_startup": "",
"no_user_logged_in": "Restart if a package or update requires it",
"user_logged_in": "Restart if a package or update requires it",
"minutes_until_reboot": 5,
"start_reboot_timer_immediately": false,
"file_vault_2_reboot": false
},
"maintenance": {
"recon": true,
"reset_name": false,
"install_all_cached_packages": false,
"heal": false,
"prebindings": false,
"permissions": false,
"byhost": false,
"system_cache": false,
"user_cache": false,
"verify": false
},
"files_processes": {
"search_by_path": "",
"delete_file": false,
"locate_file": "",
"update_locate_database": false,
"spotlight_search": "",
"search_for_process": "",
"kill_process": false,
"run_command": ""
},
"user_interaction": {
"message_start": "",
"allow_users_to_defer": false,
"allow_deferral_until_utc": "",
"allow_deferral_minutes": 0,
"message_finish": ""
},
"disk_encryption": {
"action": "none"
}
}
}
""".data(using: .utf8)
// ################################################################
// DATA STRUCTS
// ################################################################
struct ItemCodable: Codable{
let item: Item }
struct Item: Codable, Hashable, Identifiable {
var id = UUID()
let general: General?
enum CodingKeys: String, CodingKey {
case general = "general"
}
}
struct General: Codable, Hashable, Identifiable {
var id = UUID()
let name: String?
let enabled: Bool?
let trigger: String?
let triggerCheckin, triggerEnrollmentComplete, triggerLogin, triggerLogout: Bool?
let triggerNetworkStateChanged, triggerStartup: Bool?
let triggerOther, frequency: String?
let locationUserOnly: Bool?
let targetDrive: String?
let offline: Bool?
let networkRequirements: String?
let mac_address: String?
let ip_address: String?
let payloads: String?
enum CodingKeys: String, CodingKey {
case name = "name"
case enabled = "enabled"
case trigger = "trigger"
case triggerCheckin = "trigger_checkin"
case triggerEnrollmentComplete = "trigger_enrollment_complete"
case triggerLogin = "trigger_login"
case triggerLogout = "trigger_logout"
case triggerNetworkStateChanged = "trigger_network_state_changed"
case triggerStartup = "trigger_startup"
case triggerOther = "trigger_other"
case frequency = "frequency"
case locationUserOnly = "location_user_only"
case targetDrive = "target_drive"
case offline = "offline"
case networkRequirements = "network_requirements"
case mac_address = "mac_address"
case ip_address = "ip_address"
case payloads = "payloads"
}
}
// ################################################################
// DECODE DATA
// ################################################################
struct ItemsDetailReply: Codable {
// Struct to parse data
let itemDetailed: ItemCodable
static func decode(_ data: Data) -> Result<ItemCodable,Error> {
let decoder = JSONDecoder()
do {
let response = try decoder.decode(ItemsDetailReply.self, from: data)
print("ItemsDetailReply Decoding succeeded")
separationLine()
print("Response is:\n\(response)")
return .success(response.itemDetailed)
} catch {
separationLine()
print("Decoding error")
return .failure(error)
}
}
}
func separationLine() {
print("------------------------------------------------------------------")
}
// ################################################################
// DECODE AND REDIRECT TO MAIN QUEUE
// ################################################################
func processDetail(data: Data) {
// func that initiates the decoding using the decoding struct - then redirects the
// returned data to the main queue
let decoded = ItemsDetailReply.decode(data)
switch decoded {
case .success(let itemDetailed):
receivedItemDetail(itemDetailed: itemDetailed)
separationLine()
print("itemDetailed name is:\(String(describing: itemDetailed.item.general?.name))")
separationLine()
case .failure(let error):
separationLine()
print("Error encountered")
separationLine()
print(error)
separationLine()
}
}
// ################################################################
// SET PROPERTY VIA MAIN QUEUE
// ################################################################
func receivedItemDetail(itemDetailed: ItemCodable) {
DispatchQueue.main.async {
// self.itemDetailed = itemDetailed
}
}
// CALL FUNCTION
processDetail(data: data!)

Answer 1

The problem lies in the decode method:
struct ItemsDetailReply: Codable {
// Struct to parse data
let itemDetailed: ItemCodable
static func decode(_ data: Data) -> Result<ItemCodable,Error> {
let decoder = JSONDecoder()
do {
let response = try decoder.decode(ItemsDetailReply.self, from: data)
print("ItemsDetailReply Decoding succeeded")
separationLine()
print("Response is:\n\(response)")
return .success(response.itemDetailed)
} catch {
separationLine()
print("Decoding error")
return .failure(error)
}
}
}
You're trying to decode a ItemsDetailReply but the data you pass into this method represents an ItemCodable. The decoder tries to locate a top level key itemDetailed but it fails.
You can probably ditch the ItemsDetailReply struct and just decode ItemCodable like this:
let response = try decoder.decode(ItemCodable.self, from: data)