why is this not working? It's made to check if a variable with the name "language" exists at the UserDefaults.
func isKeyPresentInUserDefaults(key: String) -> Bool {
return UserDefaults.standard.object(forKey: key) != nil
}
if isKeyPresentInUserDefaults(key: language!) == true { //<-- Cannot find 'language' in scope
print("Language variable: true")
}else {
print("Language variable: false")
}
I tried to add this before the error:
let language: String?
... but it also hadn't worked.
Thank you for everyone who can help!
UserDefaults is about storing and retrieving value of variable (not it's name) using chosen key, being some String. You store the value of variable using chosen key, and then retrive stored value using the same key. What about using something like this?
let language = "language"
isKeyPresentInUserDefaults will return true if you (someone) previously stored value in UserDefaults using:
UserDefaults.default.set(someVariable, forKey: language)
Some complication (to be read as soon as text above is clear): Of course, if value of someVariable was nil, function returns false, as value nil is stored in UserDefaults. But I suppose you're not going to store Optional variable with value nil in UserDefaults.
First of all, thank you for your support. I found my own way to fix that. Hopefully it's well enough so that others later also can use this.
First, I created a new class called "UserDefaultsMonitoring.swift"
import Foundation
final class UserDefaultsMonitor {
static let shared = UserDefaultsMonitor()
public private(set) var isLanguage: Bool = false
public func startMonitoring() {
self.isLanguage = UserDefaults.standard.object(forKey: "Language") != nil
}
}
Then I added to the already by xCode created class called "ExtentionDelegate.swift" the following:
func applicationDidBecomeActive() {
// Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
UserDefaultsMonitor.shared.startMonitoring()
}
And last but not least I used this to check if the searched key exists:
if !UserDefaultsMonitor.shared.isLanguage {
NoLanguageSet()
}
Related
tldr; why do we always use UserDefaults.standard instead of subclassing UserDefaults to make something that more precisely fits our needs?
Has anyone out there subclassed UserDefaults before? Or is that considered bad practice?
Say, for example, that we make a ColorDefaults subclass of UserDefaults. When the app, the ColorDefaults object is instantiated, and that object loads all its own data. And the loaded data can then by sent to an appropriate object via delegation, or made universally available via a singleton.
My running theory is that UserDefaults is only meant to store relatively amounts of data, so having to use a singleton enforces that idea.
Bottom line: do we use UserDefaults.standard because:
subclassing is frowned upon
we're supposed to avoid saving too much data to UserDefaults in general
there's just not much value in subclassing anyway?
pretty much anything else.
Your ColorDefaults should not be a subclass of UserDefaults. It should be a plain struct or class with computed properties that are backed by UserDefaults.
Here is an example using static properties but you could refactor this to use a singleton class instead.
struct ColorDefaults {
static var someDefault: String {
get {
return UserDefaults.standard.string(forKey: "someKey") ?? "some initial value"
}
set {
UserDefaults.standard.set(newValue, forKey: "someKey")
}
}
}
let someVal = ColorDefaults.someDefault // read
ColorDefaults.someDefault = "hello" // write
This would also be useful if one of your defaults was more complicated and needed to be encoded/decoded for UserDefaults. The logic goes in here and not all over your app.
Note that such a class should only be used to store small bits of preferences, not full blown app data.
User defaults are a system of storage on file. There is little sense in subclassing unless you want to change some of its logic. But you can create multiple suits like UserDefaults(suiteName: String). What do you expect you would do with subclassing? You could simply just globally define let myDefaults = UserDefaults(suiteName: String) and use it anywhere. I guess you could use methods like
class MyDefaults: UserDefaults {
func saveName(_ name: String) {
setValue(name, forKey: "name_key")
}
}
But then again it might make more sense to just create an extension
extension UserDefaults {
func saveName(_ name: String) {
setValue(name, forKey: "name_key")
}
}
Or make it a bit more complex:
extension UserDefaults {
struct User {
static let defaults = UserDefaults(suiteName: "User")
static func saveName(_ name: String) {
defaults.setValue(name, forKey: "name")
}
}
struct General {
static let defaults = UserDefaults.standard
static func saveLastOpened(date: Date) {
defaults.setValue(date, forKey: "last_opened")
}
}
}
But all of these have one fatal flow: Now you are dependent on using user defaults within the app. At some point you may find the need to rather save these data in some other form like a local JSON file synced with iCloud. I guess UserDefaults.User could be modified to do so but would be very ugly. What we want is not UserDefaults.User.saveName("My name") but User.saveName("My name"). From the interface perspective we do not care where this user name is saved and if a new system is introduced to save these data we don't want the change in interface.
In other words, imagine you are using UserDefaults.User.saveName on 100 places in your application and now want to use another system for saving user name. You will now need to change your code on 100 places to use AnotherSystem.User.saveName while if you simply use User.saveName the interface is still valid.
So the bottom line is there is no sense in (extensively) modifying, extending or subclassing UserDefaults because it is better creating a system that wraps UserDefaults and may later be changed to any other system.
Seems you are looking for something like this
class ColorDefaults : NSObject
{
/// Save Data
class func saveDataInDefaultForKey(_ key: String, _ data: Any){
UserDefaults.standard.set(data, forKey: key)
}
/// Retrieve data
class func retrieveDataFromDefaultsWithKey(_ key: String) -> Any {
return UserDefaults.standard.value(forKey: key) as Any
}
}
Save and get data:
/// Save Data
ColorDefaults.saveDataInDefaultForKey("myArray", myArray)
ColorDefaults.saveDataInDefaultForKey("myString", myString)
/// Get Data
if let valueString = ColorDefaults.retrieveDataFromDefaultsWithKey("myString") as? String {
print("Saved Value String: \(valueString)")
}
else {
print("Error retrieving myString")
}
if let valueArray = ColorDefaults.retrieveDataFromDefaultsWithKey("myArray") as? [String] {
print("Saved Value Array: \(valueArray)")
}
else{
print("Error retrieving myArray")
}
Output:
For a project I am currently working on, it would be very useful to get the KVC-String from a KeyPath instance my method is receiving. Short example:
struct Person {
var name: String
}
let propertyCache = ["name": "something"]
func method<T>(_ keypath: KeyPath<Person, T>) -> T? {
let kvcName = keypath.kvc
return propertyCache[kvcName]
}
This might seem not very useful, but in my project it is :) I found a property on KeyPath called _kvcKeyPathString which is also public, but it returns nil every time I tried.
Or is their maybe a possibility to use reflection there? Thanks in advance for ideas/solutions!
I don't know of a pure Swift way to get the name of the property as a string yet.
But, if you add the #objc attribute to the property then _kvcKeyPathString will actually have a value instead of always being nil. Also, since Swift structs can't be represented in Objective-C, this method only works for classes.
A minimal working example usage:
class SomeClass {
#objc var someProperty = 5
}
let keyPath = \SomeClass.someProperty
print(keyPath._kvcKeyPathString)
I want to reset all my global variables when a user logs out as otherwise some of their information will stay (the info in global variables).
Is there any way to do this without manually resetting them to their initial value when the log out button is pressed?
If I understand you correctly, you are saving the user-data into a global variable? That doesn't seem to make sense for me.
If you are intending to equal NSUserDefaults as global variables, you can use the following approach to delete the Data from your standard UserDefaults:
private func cleanUserDefaultsOnLogout() {
let standardDefaults = UserDefaults.standard
for key in standardDefaults.dictionaryRepresentation().keys {
standardDefaults.removeObject(forKey: key)
}
standardDefaults.synchronize()
}
Please correct me if I've misinterpreted your question.
extension UserDefaults {
class func clean() {
guard let aValidIdentifier =
Bundle.main.bundleIdentifier else { return }
self.standard.removePersistentDomain(forName:
aValidIdentifier)
self.standard.synchronize()
}
}
use it
UserDefaults.clean()
I'm using Realm, the project is on version 1.0.0.
When I create a list of Realm Objects (with data obtained from a web API), then try to save them to the Realm using this utility function in a struct:
static func saveRealmObjects(objects: [Object]) {
defer {
// Never entered
}
for object in objects {
let realm = try! Realm()
do {
try realm.write {
print("TEST: 1: object: \(object)")
realm.add(object)
print("TEST: 2")
}
} catch {
// Never entered
}
}
}
(Please don't judge me on the exact structure, I've been toying around seeing if anything will work).
I can tell from liberal use of print statements (mostly removed above) that the function gets to TEST: 1 okay, but fails to make it to TEST: 2, for the very first Object in the list I pass to the function.
I should note this function does work the first time I use it with the data (say after wiping the simulator and launching the app afresh), but then if I recreate the Objects and try to save them again it gets stuck.
I assumed Realm would use the private key on the Objects and overwrite any if necessary. But it seems to just get stuck.
-
Then - after it's stuck - if I try and get another set of results from Realm (using a different Realm object) I get the following error:
libc++abi.dylib: terminating with uncaught exception of type realm::InvalidTransactionException: Cannot create asynchronous query while in a write transaction
FYI I'm creating a different Realm object using try! Realm()
-
For reference, here is the Object I'm trying to save:
import Foundation
import RealmSwift
class MyObject: Object {
// MARK: Realm Primary Key
dynamic var id: String = ""
override static func primaryKey() -> String? {
return "id"
}
// MARK: Stored Properties
dynamic var date: NSDate? = nil
dynamic var numA = 0
dynamic var numB = 0
dynamic var numC = 0
dynamic var numD = 0
dynamic var numE = 0
dynamic var numF = 0
dynamic var numG = 0
dynamic var numH = 0
// MARK: Computed Properties
var computedNumI: Int {
return numD + numE
}
var computedNumJ: Int {
return numF + numG
}
}
(The variable names have been changed.)
-
Hopefully I'm doing something obviously wrong - this is my first time using Realm after all.
If you have any ideas why it's sticking (perhaps it's a threading issue?), or want more info, please answer or comment. Thank you.
Being the clever clogs I am, I've literally just found the answer by reading the documentation:
https://realm.io/docs/swift/latest/#creating-and-updating-objects-with-primary-keys
The add to Realm line needed to look like this:
realm.add(object, update: true)
Where the update flag will update Objects already saved with that primary key.
-
Although it would have been nice if it either gave some sort of obvious warning or crash upon trying to add the same object, or didn't cause other queries and writes to Realm to crash.
I have an app managing a simple stocks portfolio. Amongst other things, it keeps a record of the required exchange rates in a dictionary, like so:
[ EURUSD=X : 1.267548 ]
This disctionary is a Dictionary property of a singleton called CurrencyRateStore.
When updating the stocks quotations, it checks for an updated exchange rate and updates the dictionary with the following code:
CurrencyRateStore.sharedStore()[symbol] = fetchedRate.doubleValue
That calls:
subscript(index: String) -> Double? {
get {
return dictionary[index]
}
set {
// FIXME: crashes when getting out of the app (Home button) and then relaunching it
dictionary[index] = newValue!
println("CurrencyRateStore - updated rate for \(index) : \(newValue!)")
}
}
The first time the app is started, it works fine.
But if I quit the app (with the Home button) and then relaunch it, the currency rates are updated again, but this time, I get a EXC_BAD_ACCESS at the line
dictionary[index] = newValue!
Here is a screenshot:
[EDIT] Here is the thread in the debug navigator:
I tried to update the dictionary without a subscript, like so:
CurrencyRateStore.sharedStore().dictionary[symbol] = fetchedRate.doubleValue
but without more success. Same if I use the function updateValue:forKey:
I didn't have the issue in Objective-C.
Thanks for your help !
[EDIT] Here is the whole class CurrencyRateStore:
class CurrencyRateStore {
// MARK: Singleton
class func sharedStore() -> CurrencyRateStore! {
struct Static {
static var instance: CurrencyRateStore?
static var token: dispatch_once_t = 0
}
dispatch_once(&Static.token) {
Static.instance = CurrencyRateStore()
}
return Static.instance!
}
// MARK: Properties
/** Dictionary of currency rates used by the portfolio, presented like [ EURUSD=X : 1.3624 ] */
var dictionary = [String : Double]()
/** Returns a sorted array of all the keys on the currency rates dictionary */
var allKeys: [String] {
var keysArray = Array(dictionary.keys)
keysArray.sort {$0 < $1}
return keysArray
}
init() {
if let currencyRateDictionary: AnyObject = NSKeyedUnarchiver.unarchiveObjectWithFile(currencyRateArchivePath) {
dictionary = currencyRateDictionary as [String : Double]
}
}
subscript(index: String) -> Double? {
get {
return dictionary[index]
}
set {
// FIXME: crashes when getting out of the app (Home button) and then relaunching it
// (ApplicationWillEnterForeground triggers updateStocks)
dictionary[index] = newValue!
println("CurrencyRateStore - updated rate for \(index) : \(newValue!)")
}
}
func deleteRateForKey(key: String) {
dictionary.removeValueForKey(key)
}
/** Removes all currency rates from the Currency rate store */
func deleteAllRates()
{
dictionary.removeAll()
}
// MARK: Archive items in CurrencyRateStore
var currencyRateArchivePath: String { // Archive path
var documentDirectories: Array = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
// Get the only document directory from that list
let documentDirectory: AnyObject = documentDirectories.first!
return documentDirectory.stringByAppendingPathComponent("currencyRates.archive")
}
func saveChanges()-> Bool
{
// return success or failure
return NSKeyedArchiver.archiveRootObject(dictionary, toFile: currencyRateArchivePath)
}
}
This looks to me like a concurrency issue. Swift dictionaries aren't thread safe, and using them from a singleton can lead to multiple reader/writer issues.
Edit: I am pretty sure this is the real answer, based on the given source/debugging dump. To correct what I wrote, specifically MUTABLE dictionaries and arrays (as well as NSMutableDictionary and NSMutableArray) aren't thread safe, and problems arise when using them within Singletons that are accessed from multiple threads, and that appears to be what the sample source code is doing, or enabling other parts of the code to do.
I don't have an Apple link discussing Swift collection class thread safety, but I"m pretty sure common knowledge. But the following tutorial on Grand Central Dispatch discusses the problem in depth and how to solve it using GCD.
http://www.raywenderlich.com/79149/grand-central-dispatch-tutorial-swift-part-1
The error, and the line itself:
dictionary[index] = newValue!
makes me think the problem is newValue being nil - and the error is caused by the forced unwrapping.
I would suggest to set a breakpoint and check its value, or otherwise print it before adding to the dict.
Moreover, it wouldn't be a bad idea to protect that statement with an optional binding:
if let value = newValue {
dictionary[index] = value
}
because if the value type is optional, it can be nil.
So in the end, I contacted Apple Technical Support.
They couldn't reproduce the issue.
I thought that maybe I don't need to save the currency rates, because during the quotes update, the function will check which currency rates it needs anyway, and repopulate the dictionary as needed.
So I deactivated the methods i created to save the CurrencyRateStore and to reload it again with NSKeyedUnarchiver.
Apparently, the crash is gone!