How do I use UndoManager (previously NSUndoManager) in Swift?
Here's an Objective-C example I've tried to replicate:
[[undoManager prepareWithInvocationTarget:self] myArgumentlessMethod];
Swift, however, seems to not have NSInvocation, which (seemingly) means I can't call methods on the undoManager that it doesn't implement.
I've tried the object-based version in Swift, but it seems to crash my Playground:
undoManager.registerUndoWithTarget(self, selector: Selector("myMethod"), object: nil)
However it seems to crash, even with my object accepts an argument of type AnyObject?
What's the best way to do this in Swift? Is there a way to avoid sending an unnecessary object with the object-based registration?
OS X 10.11+ / iOS 9+ Update
(Works the same in Swift 3 as well)
OS X 10.11 and iOS 9 introduce a new NSUndoManager function:
public func registerUndoWithTarget<TargetType>(target: TargetType, handler: TargetType -> ())
Example
Imagine a view controller (self in this example, of type MyViewController) and a Person model object with a stored property name.
func setName(name: String, forPerson person: Person) {
// Register undo
undoManager?.registerUndoWithTarget(self, handler: { [oldName = person.name] (MyViewController) -> (target) in
target.setName(oldName, forPerson: person)
})
// Perform change
person.name = name
// ...
}
Caveat
If you're finding your undo isn't (ie, it executes but nothing appears to have happened, as if the undo operation ran but it's still showing the value you wanted to undo from), consider carefully what the value (the old name in the example above) actually is at the time the undo handler closure is executed.
Any old values to which you want to revert (like oldName in this example) must be captured as such in a capture list. That is, if the closure's single line in the example above were instead:
target.setName(person.name, forPerson: person)
...undo wouldn't work because by the time the undo handler closure is executed, person.name is set to the new name, which means when the user performs an undo, your app (in the simple case above) appears to do nothing since it's setting the name to its current value, which of course isn't undoing anything.
The capture list ([oldName = person.name]) ahead of the signature ((MyViewController) -> ()) declares oldName to reference person.name as it is when the closure is declared, not when it's executed.
More Information About Capture Lists
For more information about capture lists, there's a great article by Erica Sadun titled Swift: Capturing references in closures. It's also worth paying attention to the retain cycle issues she mentions. Also, though she doesn't mention it in her article, inline declaration in the capture list as I use it above comes from the Expressions section of the Swift Programming Language book for Swift 2.0.
Other Ways
Of course, a more verbose way to do it would be to let oldName = person.name ahead of your call to registerUndoWithTarget(_:handler:), then oldName is automatically captured in scope. I find the capture list approach easier to read, since it's right there with the handler.
I also completely failed to get registerWithInvocationTarget() to play nice with non-NSObject types (like a Swift enum) as arguments. In the latter case, remember that not only should the invocation target inherit from NSObject, but the arguments to the function you call on that invocation target should as well. Or at least be types that bridge to Cocoa types (like String and NSString or Int and NSNumber, etc.). But there were also problems with the invocation target not being retained that I just couldn't solve. Besides, using a closure as a completion handler is far more Swiftly.
In Closing (Get it?)
Figuring all this out took me several hours of barely-controlled rage (and probably some concern on the part of my Apple Watch about my heart rate - "tap-tap! dude... been listening to your heart and you might want to meditate or something"). I hope my pain and sacrifice helps. :-)
Update 2: Swift in Xcode 6.1 has made undoManager an optional so you call prepareWithInvocationTarget() like this:
undoManager?.prepareWithInvocationTarget(myTarget).insertSomething(someObject, atIndex: index)
Update: Swift in Xcode6 beta5 simplified use of undo manager's prepareWithInvocationTarget().
undoManager.prepareWithInvocationTarget(myTarget).insertSomething(someObject, atIndex: index)
Below was what was needed in beta4:
The NSInvocation based undo manager API can still be used, although it wasn't obvious at first how to call it. I worked out how to call it successfully using the following:
let undoTarget = undoManager.prepareWithInvocationTarget(myTarget) as MyTargetClass?
undoTarget?.insertSomething(someObject, atIndex: index)
Specifically, you need to cast the result of prepareWithInvocationTarget() to the target type, although remember to make it optional or you get a crash (on beta4 anyway). Then you can call your typed optional with the invocation you want to record on the undo stack.
Also make sure your invocation target type inherits from NSObject.
I tried this in a Playground and it works flawlessly:
class UndoResponder: NSObject {
#objc func myMethod() {
print("Undone")
}
}
var undoResponder = UndoResponder()
var undoManager = UndoManager()
undoManager.registerUndo(withTarget: undoResponder, selector: #selector(UndoResponder.myMethod), object: nil)
undoManager.undo()
I tried for 2 days to get Joshua Nozzi's answer to work in Swift 3, but no matter what I did the values were not captured.
See: NSUndoManager: capturing reference types possible?
I gave up and just managed it myself by keeping track of changes in undo and redo stacks. So, given a person object I would do something like
protocol Undoable {
func undo()
func redo()
}
class Person: Undoable {
var name: String {
willSet {
self.undoStack.append(self.name)
}
}
var undoStack: [String] = []
var redoStack: [String] = []
init(name: String) {
self.name = name
}
func undo() {
if self.undoStack.isEmpty { return }
self.redoStack.append(self.name)
self.name = self.undoStack.removeLast()
}
func redo() {
if self.redoStack.isEmpty { return }
self.undoStack.append(self.name)
self.name = self.redoStack.removeLast()
}
}
Then to call it, I don't worry about passing arguments or capturing values since the undo/redo state is managed by the object itself. So say you have a ViewController that is managing your Person objects, you just call registerUndo and pass nil
undoManager?.registerUndo(withTarget: self, selector:#selector(undo), object: nil)
I think it would be Swiftiest if NSUndoManager accepted a closure as an undo registration. This extension will help:
private class SwiftUndoPerformer: NSObject {
let closure: Void -> Void
init(closure: Void -> Void) {
self.closure = closure
}
#objc func performWithSelf(retainedSelf: SwiftUndoPerformer) {
closure()
}
}
extension NSUndoManager {
func registerUndo(closure: Void -> Void) {
let performer = SwiftUndoPerformer(closure: closure)
registerUndoWithTarget(performer, selector: Selector("performWithSelf:"), object: performer)
//(Passes unnecessary object to get undo manager to retain SwiftUndoPerformer)
}
}
Then you can Swift-ly register any closure:
undoManager.registerUndo {
self.myMethod()
}
setValue forKey does the trick for me on OS X if one needs to support 10.10. I couldn't set it directly cause prepareWithInvocationTarget returns a proxy object.
#objc
enum ImageScaling : Int, CustomStringConvertible {
case FitInSquare
case None
var description : String {
switch self {
case .FitInSquare: return "FitInSquare"
case .None: return "None"
}
}
}
private var _scaling : ImageScaling = .FitInSquare
dynamic var scaling : ImageScaling {
get {
return _scaling
}
set(newValue) {
guard (_scaling != newValue) else { return }
undoManager?.prepareWithInvocationTarget(self).setValue(_scaling.rawValue, forKey: "scaling")
undoManager?.setActionName("Change Scaling")
document?.beginChanges()
_scaling = newValue
document?.endChanges()
}
}
I too have done a bit of reading and came up with the following: I have 2 tableViews, source by a dictionary and array controller for playlists and its items respectively, which I'm adding to the Helium 3 project on GitHub (not there yet); here's a preview:
dynamic var playlists = Dictionary<String, Any>()
dynamic var playCache = Dictionary<String, Any>()
// MARK:- Undo keys to watch for undo: dictionary(list) and play item
var listIvars : [String] {
get {
return ["key", "value"]
}
}
var itemIvars : [String] {
get {
return ["name", "temp", "time", "rank", "rect", "label", "hover", "alpha", "trans"]
}
}
internal func observe(_ item: AnyObject, keyArray keys: [String], observing state: Bool) {
switch state {
case true:
for keyPath in keys {
item.addObserver(self, forKeyPath: keyPath, options: [.old,.new], context: nil)
}
break
case false:
for keyPath in keys {
item.removeObserver(self, forKeyPath: keyPath)
}
}
}
// Start or forget observing any changes
internal func observing(_ state: Bool) {
for dict in playlists {
let items: [PlayItem] = dict.value as! [PlayItem]
self.observe(dict as AnyObject, keyArray: listIvars, observing: state)
for item in items {
self.observe(item, keyArray: itemIvars, observing: state)
}
}
}
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
if let undo = self.undoManager {
let oldValue = change?[NSKeyValueChangeKey(rawValue: "old")]
let newValue = change?[NSKeyValueChangeKey(rawValue: "new")]
undo.registerUndo(withTarget: self, handler: {[oldVals = ["key": keyPath!, "old": oldValue as Any] as [String : Any]] (PlaylistViewController) -> () in
(object as AnyObject).setValue(oldVals["old"], forKey: oldVals["key"] as! String)
if !undo.isUndoing {
undo.setActionName(String.init(format: "Edit %#", keyPath!))
}
})
Swift.print(String.init(format: "%# %# -> %#", keyPath!, oldValue as! CVarArg, newValue as! CVarArg))
}
}
override func viewWillAppear() {
// Start observing any changes
observing(true)
}
override func viewDidDisappear() {
// Stop observing any changes
observing(false)
}
// "List" items are controller objects - NSDictionaryControllerKeyValuePair
internal func addList(_ item: NSDictionaryControllerKeyValuePair, atIndex index: Int) {
if let undo = self.undoManager {
undo.registerUndo(withTarget: self, handler: {[oldVals = ["item": item, "index": index] as [String : Any]] (PlaylistViewController) -> () in
self.removeList(oldVals["item"] as! NSDictionaryControllerKeyValuePair, atIndex: oldVals["index"] as! Int)
if !undo.isUndoing {
undo.setActionName("Add PlayList")
}
})
}
observe(item, keyArray: listIvars, observing: true)
playlistArrayController.insert(item, atArrangedObjectIndex: index)
DispatchQueue.main.async {
self.playlistTableView.scrollRowToVisible(index)
}
}
internal func removeList(_ item: NSDictionaryControllerKeyValuePair, atIndex index: Int) {
if let undo = self.undoManager {
undo.prepare(withInvocationTarget: self.addList(item, atIndex: index))
if !undo.isUndoing {
undo.setActionName("Remove PlayList")
}
}
if let undo = self.undoManager {
undo.registerUndo(withTarget: self, handler: {[oldVals = ["item": item, "index": index] as [String : Any]] (PlaylistViewController) -> () in
self.addList(oldVals["item"] as! NSDictionaryControllerKeyValuePair, atIndex: oldVals["index"] as! Int)
if !undo.isUndoing {
undo.setActionName("Remove PlayList")
}
})
}
observe(item, keyArray: listIvars, observing: false)
playlistArrayController.removeObject(item)
DispatchQueue.main.async {
self.playlistTableView.scrollRowToVisible(index)
}
}
"List" items are NSDictionaryControllerKeyValuePair for the NSDictionaryController.
The "item" handling is a bit more complicated but this should get you going. Each time a list or item is added/removed the proper the add|remove method is called. Then you start observing as new items appear and forget as they're removed, this also observes each object's ivars for changes.
Enjoy.
My current take on this:
protocol Undoable {
func inverted() -> Self
}
class Store<State, Action : Undoable> {
let undoManager : UndoManager
let state : State
let reducer : (inout State, Action) -> Void
//...init...
func send(_ action: Action) {
reducer(&state, action)
undoManager.registerUndo(withTarget: self){target in
target.send(action.inverted())
}
}
}
Works great if you're able to get the correct UndoManager. In SwiftUI, this seems to be tricky though, the one in the Environment does not seem to always be the one associated with command+z or Edit -> Undo (I even tried passing it as an argument to send from each View!), and even making it a computed property like below didn't solve my problem:
var undoManager : UndoManager? {
NSApplication.shared.keyWindow.undoManager
}
Edit: my bad, passing it as a function argument works just fine. Just not from sheets apparently, because they're in their own NSWindow... One has to pass the proper UndoManager down then. If the sheet has a deeply nested view hierarchy, one should pass it through a custom EnvironmentValue.
Related
Let's say I have a Swift class that stores a completion block, and does a few asynchronous tasks.
I want that block to be called by whichever of the tasks finishes first, but only that one - I don't want it to be called again when the second task finishes.
How can I implement this in a clean way?
As long as you don't need this to be thread safe, you can solve this problem with a fairly straightforward #propertyWrapper.
#propertyWrapper
struct ReadableOnce<T> {
var wrappedValue: T? {
mutating get {
defer { self._value = nil }
return self._value
}
set {
self._value = newValue
}
}
private var _value: T? = nil
}
Mark the completion block var with #ReadableOnce, and it will be destroyed after the first time it's value is read.
Something like this:
class MyClass {
#ReadableOnce private var completion: ((Error?) -> Void)?
init(completion: #escaping ((Error?) -> Void)) {
self.completion = completion
}
public func doSomething() {
// These could all be invoked from different places, like your separate tasks' asynchronous callbacks
self.completion?(error) // This triggers the callback, then the property wrapper sets it to nil.
self.completion?(error) // This does nothing
self.completion?(error) // This does nothing
}
}
I wrote up more of a detailed discussion of this here but the key thing to be aware of is that reading the value sets it to nil, even if you don't invoke the closure! This might be surprising to someone who isn't familiar with the clever property wrapper you've written.
There is already a standard expression of onceness. Unfortunately the standard Objective-C is unavailable in Swift (GCD dispatch_once), but the standard Swift technique works fine, namely a property with a lazy define-and-call initializer.
Exactly how you do this depends on the level at which you want onceness to be enforced. In this example it's at the level of the class instance:
class MyClass {
// private part
private let completion : (() -> ())
private lazy var once : Void = {
self.completion()
}()
private func doCompletionOnce() {
_ = self.once
}
// public-facing part
init(completion:#escaping () -> ()) {
self.completion = completion
}
func doCompletion() {
self.doCompletionOnce()
}
}
And here we'll test it:
let c = MyClass() {
print("howdy")
}
c.doCompletion() // howdy
c.doCompletion()
let cc = MyClass() {
print("howdy2")
}
cc.doCompletion() // howdy2
cc.doCompletion()
If you promote the private stuff to the level of the class (using a static once property), the completion can be performed only once in the lifetime of the entire program.
I don't clear about these two, Nowadays the world is shifting to the closure types. But I'm not clearly understanding this. Can someone explain me with a real-time example?
So a real life example of both would be something like this:
protocol TestDelegateClassDelegate: class {
func iAmDone()
}
class TestDelegateClass {
weak var delegate: TestDelegateClassDelegate?
func doStuff() {
DispatchQueue.main.asyncAfter(deadline: .now() + 3.0) {
self.delegate?.iAmDone()
}
}
}
class TestClosureClass {
var completion: (() -> Void)?
func doStuff() {
DispatchQueue.main.asyncAfter(deadline: .now() + 3.0) {
self.completion?()
}
}
}
class ViewController: UIViewController, TestDelegateClassDelegate {
func iAmDone() {
print("TestDelegateClassDelegate is done")
}
override func viewDidLoad() {
super.viewDidLoad()
let testingDelegate = TestDelegateClass()
testingDelegate.delegate = self
testingDelegate.doStuff()
let testingClosure = TestClosureClass()
testingClosure.completion = {
print("TestClosureClass is done")
}
testingClosure.doStuff()
}
}
Here we have 2 classes TestDelegateClass and TestClosureClass. Each of them have a method doStuff which waits for 3 seconds and then reports back to whoever is listening where one uses delegate procedure and the other one uses closure procedure.
Although they do nothing but wait you can easily imagine that they for instance upload an image to server and notify when they are done. So for instance you might want to have an activity indicator running while uploading is in progress and stop it when done. It would look like so:
class ViewController: UIViewController, TestDelegateClassDelegate {
#IBOutlet private var activityIndicator: UIActivityIndicatorView?
func iAmDone() {
print("TestDelegateClassDelegate is done")
activityIndicator?.stopAnimating()
}
override func viewDidLoad() {
super.viewDidLoad()
activityIndicator?.startAnimating()
let testingDelegate = TestDelegateClass()
testingDelegate.delegate = self
testingDelegate.doStuff()
activityIndicator?.startAnimating()
let testingClosure = TestClosureClass()
testingClosure.completion = {
self.activityIndicator?.stopAnimating()
print("TestClosureClass is done")
}
testingClosure.doStuff()
}
}
Naturally you would only use one of the two procedures.
You can see there is a huge difference in code. To do a delegate procedure you need to create a protocol, in this case TestDelegateClassDelegate. A protocol is what defines the interface of a listener. And since an iAmDone method is defined it must be defined in ViewController as well as long as it is defined as TestDelegateClassDelegate. Otherwise it will not compile. So anything declared as TestDelegateClassDelegate will have that method and any class can call it. In our case we have weak var delegate: TestDelegateClassDelegate?. That is why we can call delegate?.iAmDone() without caring what delegate actually is. For instance we can create another class:
class SomeClass: TestDelegateClassDelegate {
func iAmDone() {
print("Something cool happened")
}
init() {
let testingDelegate = TestDelegateClass()
testingDelegate.delegate = self
testingDelegate.doStuff()
}
}
So a good example for instance is an UITableView that uses a delegate and dataSource (both are delegates, just properties are named differently). And table view will call the methods of whatever class you set to those properties without needing to know what that class is as long as it corresponds to the given protocols.
Same could be achieved with closures. A table view could have been defined using properties giving closures like:
tableView.onNumberOfRows { section in
return 4
}
But that would most likely lead into one big mess of a code. Also closures would in this case be giving many programmers headaches due to potential memory leaks. It is not that closures are less safe or anything, they just do a lot of code you can't see which may produce retain cycles. In this specific case a most likely leak would be:
tableView.onNumberOfRows { section in
return self.dataModel.count
}
and a fix to it is simply doing
tableView.onNumberOfRows { [weak self] section in
return self?.dataModel.count ?? 0
}
which now looks overcomplicated.
I will not go into depths of closures but in the end when you have repeated call to callbacks (like in case of table view) you will need a weak link either at delegate or in closure. But when the closure is called only once (like uploading an image) there is no need for a weak link in closures (in most but not all cases).
In retrospective use closures as much as possible but avoid or use caution as soon as a closure is used as a property (which is ironically the example I gave). But you would rather do just this:
func doSomethingWithClosure(_ completion: #escaping (() -> Void)) {
DispatchQueue.main.asyncAfter(deadline: .now() + 3.0) {
completion()
}
}
And use it as
doSomethingWithClosure {
self.activityIndicator?.stopAnimating()
print("TestClosureClass is done")
}
This has now removed all potential risks. I hope this clears a thing or two for you.
In Swift/obj-c the term delegate is used to refer to a protocol that responds to specific selectors.
Thing about it just like calling a method on an object.
E.g.
protocol CalculatorDelegate : class { // : class so it can be made 'weak'
func onCalculation(result: Int) -> Void
}
Now if we have a Calculator class, to use the delegate we'd do something like
class Calculator() {
weak var delegate: CalculatorDelegate?
func calculate(_ a: Int, _ b: Int) -> Int {
let result = a + b
self.delegate?.onCalculation(result: result)
return result
}
}
Then in some other class (e.g. in iOS - a View Controller) we might do:
class MyClass : CalculatorDelegate {
func onCalculation(result: Int) {
print("Delegate method on calculation called with result \(result)")
}
func someButtonPress() {
let calculator = Calculator()
calculator.delegate = self
calculator.calculate(42, 66)
}
}
So you can see how the setup is quite elaborate.
Now closures are simply blocks of code that can be called in other places, so you could change all of the code like so:
class Calculator2() {
weak var delegate: CalculatorDelegate?
func calculate(_ a: Int, _ b: Int, onCalculation: (#escaping (Int) -> Void) -> Int)?) {
let result = a + b
onCalculation?(result)
return result
}
}
class MyClass {
func someButtonPress() {
let calculator = Calculator2()
calculator.calculate(42, 66, onCalculation: { (result: Int) in
print("Closure invoked with \(result)")
})
}
}
However, with closures you need to be aware that it is a lot easier to shoot yourself in the foot by capturing variables (e.g. self) strongly, which will lead to memory leaks even under ARC regime.
Closures are first-class objects so that they can be nested and passed around
Simply,
In swift, functions are primitive data types like int, double or character that is why you can pass a function in the function parameter. In swift mechanism simplify in closures syntax like lambda expression in other languages.
E.g. If you want to call rest API through URSSession or Alamofire and return response data then you should use completionHandler(it's closure).
Void closure : - {(paramter:DataType)->Void}
Return closure : - {(paramter:DataType)->DataType}
e.g. (int, int) -> (int)
https://docs.swift.org/swift-book/LanguageGuide/Closures.html
I have Singleton class to which i have used to observe a property and trigger next action.
Singleton Class:
public class BridgeDispatcher: NSObject {
open var shouldRespondToBridgeEvent = SafePublishSubject<[String: Any]>()
open var shouldPop = SafePublishSubject<Void>()
open var shouldUpdate = SafePublishSubject<Void>()
public let disposeBag = DisposeBag()
open static let sharedInstance: BridgeDispatcher = BridgeDispatcher()
override init() {
super.init()
shouldRespondToBridgeEvent.observeNext { event in
if let type = event["type"] as? String {
switch type {
case "ShouldUpdate":
self.onShiftBlockDidUpdateHeight.next()
case "shouldPop":
self.onPopCurrentViewController.next(())
default:
print("Event not supported")
}
}
}.dispose(in: self.disposeBag)
}
}
Above method will trigger by calling:
BridgeDispatcher.sharedInstance.shouldRespondToBridgeEvent.next(body)
Register for onPopCurrentViewController:
BridgeDispatcher.sharedInstance.onPopCurrentViewController.observeNext { doSomething() }.dispose(in: BridgeDispatcher.sharedInstance.disposeBag)
On my application, BridgeDispatcher.sharedInstance.onPopCurrentViewController.observeNext{} method will be called multiple times due to the business logic, due to this doSomething() method will trigger multiple times when calling BridgeDispatcher.sharedInstance.shouldRespondToBridgeEvent.next(body).
Is this issue with my singleton design pattern or observeNext calling multiple times. (BridgeDispatcher.sharedInstance.onPopCurrentViewController.observeNext{} )
Need help.
I have used .updateSignal on ObservableComponent.
valueToUpdate.updateSignal.compactMap { (arg0) -> String? in
let (value, _, validationFailure) = arg0
return validationFailure == nil ? value?.value : nil
}
.removeDuplicates()
.debounce(for: 1.0)
.observeNext { [unowned self] _ in
self.doYourWork()
}
.dispose(in: self.bag)
It attempts to deal with the multiple calls in two ways: first by discarding any duplicate events, so if the duration hasn’t changed, then no call is made. Second, by debouncing the signal so if the user makes a bunch of changes we only call the method when they’re done making changes.
Motivation is to get a trigger for recalculation upon changes on values of Entity.
My quick solution cited below works, but it has drawbacks. It is inefficient.
In actual App, there are tens of entities. Changes on any of them will cause unnecessary notifications. Those could be avoided, if possible.
In this example, the only EmployeeMO is interested. No other entity needs to be observed.
What is your thoughts?
let n = NotificationCenter.default
n.addObserver(self, selector: #selector(mocDidChange(notification:)),
name: NSNotification.Name.NSManagedObjectContextObjectsDidChange,
object: managedObjectContext)
#objc func mocDidChange(notification n: Notification) {
if n.isRelatedTo(as: EmployeeMO.self) {
// do recalculation
}
}
And an extension to check if the notification is related to a given managed object:
extension Notification {
public func isRelatedTo<T>(as t: T.Type) -> Bool where T: NSManagedObject {
typealias S = Set<T>
let d = userInfo as! [String : Any]
return d[NSInsertedObjectsKey] is S ||
d[NSUpdatedObjectsKey] is S ||
d[NSDeletedObjectsKey] is S ||
d[NSRefreshedObjectsKey] is S ||
d[NSInvalidatedObjectsKey] is S
}
}
Xcode 9 Beta, Swift 4
Thanks.
The is a built in object that does exactly this already - NSFetchedResultsController. It is designed to work with a tableview or collectionView, but can work fine without one. It is lightweight enough that it is safe to use for just one object.
Thanks to #jon, now my source code has been greatly improved.
class myBaseArrayController: NSArrayController, NSFetchedResultsControllerDelegate {
// https://developer.apple.com/documentation/coredata/nsfetchedresultscontroller
var frc: NSFetchedResultsController<NSManagedObject>?
func setupObserver() {
frc = NSFetchedResultsController(fetchRequest: defaultFetchRequest() as! NSFetchRequest<NSManagedObject>,
managedObjectContext: managedObjectContext!,
sectionNameKeyPath: nil, cacheName: nil)
frc?.delegate = self
do {
try frc?.performFetch()
}
catch {
fatalError("...")
}
}
}
Every ArrayController for its corresponding entity simply implements controllerDidChangeContent().
class myOneOfThemArrayController: myBaseArrayController {
func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
print("controllerDidChangeContent: \(controller.fetchRequest.entityName)")
// do some work
}
}
No more comparison to find which is what for. :-)
Given an instance of a class, how can I observe a property change?
For e.g., I'm building an SDK that initializes a host app's chat view to provide more functionality with a simple inplementation that looks like:
sdk.initialize(chatView)
In that initializing function, I need to track the host app's chat-view's hidden property so that the SDK's view matches.
A simple KVO example for observing hidden:
class SDKViewController : UIViewController {
private var context = 0
private var observingView: UIView?
func initialize(view: UIView) {
removeObservations()
observingView = view
// start observing changes to hidden property of UIView
observingView?.addObserver(self, forKeyPath: "hidden", options: [.New], context: &context)
}
override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
if let newValue = change?[NSKeyValueChangeNewKey] as? Bool where context == &self.context {
print("hidden changed: \(newValue)")
}
}
// this is called by deinit
// it should also be called if they can deregister the view from your SDK
func removeObservations() {
if let view = observingView {
view.removeObserver(self, forKeyPath: "hidden")
observingView = nil
}
}
deinit {
removeObservations()
}
}
This is making some assumptions about your configuration, but if you allow initialization of many views, you can adjust easily.
Also, a lot of this is more concise if you use KVOController by Facebook, which is not in Swift.
Edit: Just to note, hidden does work with KVO.
Edit #2: Updated YourSDKClass to SDKViewController (NSObject -> UIViewController)
Here is an example using protocols
protocol MyClassDelegate:class {
func myClassValueDidChange(newValue:Int)
}
class MyClass {
weak var delegate:MyClassDelegate?
var value = 0 {
didSet {
delegate?.myClassValueDidChange(value)
}
}
}
class ViewController:UIViewController,MyClassDelegate {
let myClass = MyClass()
override func viewDidLoad() {
super.viewDidLoad()
myClass.delegate = self
}
func myClassValueDidChange(newValue:Int) {
//Do something
}
}
You can use Key Value Observing (KVO) to monitor changes to general properties on classes, which includes the hidden property on UIView instances. This is done using addObserver:forKeyPath:options:context: defined in the NSKeyValueObserving protocol.
Note that you can also hide a view by removing it from its superview or by setting its alpha to zero.