Related
I'm trying to build an app (macOS, but would be the same for iOS) that creates a number of grids, the outcome of which is to be shown in a second screen. For this, I'm sharing data across these screens, and I'm running into an issue here, I hope someone can help or point me in the right direction. I'll share a simplified version of the code below (working in Xcode 14.0.1)
The code creates a dictionary that can be shown in a grid, on which calculations can be done. The idea is then to add this grid, with some descriptive variables, into another dictionary
The building blocks of the grid are cells
Import Foundation
struct Cell: Comparable, Equatable, Identifiable, Hashable {
static func == (lhs: Cell, rhs: Cell) -> Bool {
lhs.randomVarOne == rhs.randomVarOne
}
var randomVarOne: Double
var randomVarTwo: Bool
// other vars omitted here
var id: Int { randomVarOne }
static func < (lhs: Cell, rhs: Cell) -> Bool {
return lhs.randomVarOne < rhs.randomVarOne
}
}
this is also where there are a bunch of funcs to calculate next neighbor cells in the grid etc
then the grid is defined in a class:
class Info: ObservableObject, Hashable {
static func == (lhs: Info, rhs: Info) -> Bool {
lhs.grid == rhs.grid
}
func hash(into hasher: inout Hasher) {
hasher.combine(grid)
}
#Published var grid = [Cell]()
var arrayTotal = 900
#Published var toBeUsedForTheGridCalculations: Double = 0.0
var toBeUsedToSetTheVarAbove: Double = 0.0
var rowTotalDouble: Double {sqrt(Double(arrayTotal)) }
var rowTotal: Int {
Int(rowTotalDouble) != 0 ? Int(rowTotalDouble) : 10 }
The class includes a func to create and populate the grid with Cells and add these Cells to the grid var. It also includes the formulas to do the calculations on the grid using a user input. The class did not seem to need an initializer.
This is the Scenario struct:
struct Scenario: Comparable, Equatable, Identifiable, Hashable {
static func == (lhs: Scenario, rhs: Scenario) -> Bool {
lhs.scenarioNumber == rhs.scenarioNumber
}
func hash(into hasher: inout Hasher) {
hasher.combine(scenarioNumber)
}
var scenarioNumber: Int
var date: Date
var thisIsOneSnapshot = [Info]()
var id: Int { scenarioNumber }
static func < (lhs: Scenario, rhs: Scenario) -> Bool {
return lhs.scenarioNumber < rhs.scenarioNumber
}
}
added hashable since it uses the Info class as an input.
Then there is the class showing the output overview
class OutputOverview: ObservableObject {
#Published var snapshot = [Scenario]()
// the class includes a formula of how to add the collection of cells (grid) and the additional variables to the snapshot dictionary. Again no initializer was necessary.
Now to go to the ContentView.
struct ContentView: View {
#Environment(\.openURL) var openURL
var scenarioNumberInput: Int = 0
var timeStampAssigned: Date = Date.now
#ObservedObject private var currentGrid: Info = Info()
#ObservedObject private var scenarios: Combinations = Combinations()
var usedForTheCalculations: Double = 0.0
var rows =
[
GridItem(.flexible()),
// whole list of GridItems, I do not know how to calculate these:
// var rows = Array(repeating: GridItem(.flexible()), count: currentGrid.rowTotal)
//gives error "Cannot use instance member 'currentGrid' within property initializer;
// property iunitializers run before 'self' is available
]
var body: some View {
GeometryReader { geometry in
VStack {
ScrollView {
LazyHGrid(rows: rows, spacing: 0) {
ForEach(0..<currentGrid.grid.count, id :\.self) { w in
let temp = currentGrid.grid[w].varThatAffectsFontColor
let temp2 = currentGrid.grid[w].varThatAffectsBackground
Text("\(currentGrid.grid[w].randomVarOne, specifier: "%.2f")")
.frame(width: 25, height: 25)
.border(.black)
.font(.system(size: 7))
.foregroundColor(Color(wordName: temp))
.background(Color(wordName: temp2))
}
}
.padding(.top)
}
VStack{
HStack {
Button("Start") {
}
// then some buttons to do the calculations
Button("Add to collection"){
scenarios.addScenario(numbering: scenarioNumberInput, timeStamp:
Date.now, collection: currentGrid.grid)
} // this should add the newly recalculated grid to the dictionary
Button("Go to Results") {
guard let url = URL(string: "myapp://scenario") else { return }
openURL(url)
} // to go to the screen showing the scenarios
Then the second View, the ScenarioView:
struct ScenarioView: View {
#State var selectedScenario = 1
#ObservedObject private var scenarios: OutputOverview
var pickerNumbers = [ 1, 2, 3, 4 , 5]
// this is to be linked to the number of scenarios completed,this code is not done yet.
var rows =
[
GridItem(.flexible()),
GridItem(.flexible()),
// similar list of GridItems here....
var body: some View {
Form {
Section {
Picker("Select a scenario", selection: $selectedScenario) {
ForEach(pickerNumbers, id: \.self) {
Text("\($0)")
}
}
}
Section {
ScrollView {
if let idx = scenarios.snapshot.firstIndex(where:
{$0.scenarioNumber == selectedScenario}) {
LazyHGrid(rows: rows, spacing: 0) {
ForEach(0..<scenarios.snapshot[idx].thisIsOneSnapshot.count,
id :\.self) { w in
let temp =
scenarios.snapshot[idx].thisIsOneSnapshot[w].varThatAffectsFontColor
let temp2 =
scenarios.snapshot[idx].thisIsOneSnapshot[w].varThatAffectsBackground
Text("\(scenarios.snapshot[idx].thisIsOneSnapshot[w].randomVarOne, specifier: "%.2f")")
.frame(width: 25, height: 25)
.border(.black)
.font(.system(size: 7))
.foregroundColor(Color(wordName: temp))
.background(Color(wordName: temp2))
}
}
}
}
}
}
}
}
Now while the above does not (for the moment..) give me error messages, I am not able to run the PreviewProvider in the second View. The main problem is in #main:
import SwiftUI
#main
struct ThisIsTheNameOfMyApp: App {
var body: some Scene {
WindowGroup {
ContentView()
}
.handlesExternalEvents(matching: ["main"])
WindowGroup("Scenarios") {
ScenarioView()
// error messages here: 'ScenarioView' initializer is inaccessible due to "private"
// protection level - I don't know what is set to private in ScenarioView that could
// cause this
// second error message: missing argument for parameter 'scenarios' in call
}
.handlesExternalEvents(matching: ["scenario"])
}
}
I am at a loss on how to solve these 2 error messages and would be very grateful for any tips or guidance. Apologies if this question is very long, I scanned many other forum questions and could not find any good answers.
I have tried adding pro forma data in #main as follows
#main
struct FloodModelScenarioViewerApp: App {
#State var scenarios = Scenario(scenarioNumber: 1, date: Date.now)
var body: some Scene {
WindowGroup {
ContentView()
}
.handlesExternalEvents(matching: ["main"])
WindowGroup("Scenarios") {
ScenarioView(scenarios: scenarios)
}
.handlesExternalEvents(matching: ["scenario"])
}
}
This still gives 2 error messages:
same issue with regards to ScenarioView initialiser being inaccessible due to being 'private'
Cannot convert value of type 'Scenario' to expected argument type 'OutputOverview'
Just remove the private from
#ObservedObject private var scenarios: OutputOverview
The value is coming from he parent so the parent needs access. So put
#StateObject private var scenarios: OutputOverview = .init()
in FloodModelScenarioViewerApp
#StateObject is for initializing ObservableObjects and #ObservedObject is for passing them around.
I don't know if your code will work after you read this question, and that's because there are many things to correct, but you can start with these:
In Cell, you shouldn't use an id that is a variable, this may cause inconsistent behavior. Use something like:
let id = UUID()
When you initialize ContentView, you can't use currentGrid inside a variable because currentGrid will not be available before all variables are initialized. Meaning, you are trying to initialize rows before currentGrid actually exists. You can try using the .onAppear modifier:
var rows = [GridItem]()
var body: some View {
GeometryReader { geometry in
// ... view code in here
}
.onAppear {
var rows = Array(repeating: GridItem(.flexible()), count: currentGrid.rowTotal)
}
}
This creates the view and, before showing it, the grid is set to its proper value.
The message 'ScenarioView' initializer is inaccessible due to "private" protection level seems clear: you must provide a value to to the variable scenarios (it doesn't have a default value) but it's marked as private. Remove private.
#ObservedObject var scenarios: OutputOverview
Then, remember to pass a value of type OutputOverview for the variable when you call the view:
ScenarioView(scenarios: aVariableOfTypeOutputOverview)
The type mismatch error you get inside the #main code is also clear - you have defined a variable of type Scenario:
#State var scenarios = Scenario(scenarioNumber: 1, date: Date.now)
but ScenarioView requires another type:
#ObservedObject private var scenarios: OutputOverview
One of them needs change for your code to work.
Sorry if that title is not clear enough but I didn't know how to sum it up in one sentence.
I have a webservice that returns an ArrayList of objects named Father.
The Father object is structured like this:
class Father {
ArrayList<Child> children;
}
I have another webservice that returns me the detail of the object Child.
How can I concat the first call that returns me the arraylist of Father and the multiple calls for the multiple objects Child ?
So far I can make the calls separately, like this:
Call for ArrayList of Father
myRepository.getFathers().subscribeOn(Schedulers.io())
.observeOn(Schedulers.io()).subscribeWith(new DisposableSingleObserver<List<Father>>() {
})
multiple call for ArrayList of Child
childListObservable
.subscribeOn(Schedulers.io())
.observeOn(Schedulers.io())
.flatMap((Function<List<Child>, ObservableSource<Child>>) Observable::fromIterable)
.flatMap((Function<Child, ObservableSource<Child>>) this::getChildDetailObservable)
.subscribeWith(new DisposableObserver<Child>() {
// do whatever action after the result of each Child
}))
Prerequisite
Gradle
implementation("io.reactivex.rxjava2:rxjava:2.2.10")
testImplementation("io.mockk:mockk:1.10.0")
testImplementation("org.assertj:assertj-core:3.11.1")
testImplementation("org.junit.jupiter:junit-jupiter-api:5.3.1")
testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.3.1")
Classes / Interfaces
interface Api {
fun getFather(): Single<List<Father>>
fun childDetailInfo(child: Child): Single<ChildDetailInfo>
}
interface Store {
fun store(father: Father): Completable
fun store(child: ChildDetailInfo): Completable
}
class ApiImpl : Api {
override fun getFather(): Single<List<Father>> {
val child = Child("1")
val child1 = Child("2")
return Single.just(listOf(Father(listOf(child, child1)), Father(listOf(child))))
}
override fun childDetailInfo(child: Child): Single<ChildDetailInfo> {
return Single.just(ChildDetailInfo(child.name))
}
}
data class Father(val childes: List<Child>)
data class Child(val name: String)
data class ChildDetailInfo(val name: String)
Solution
val fathersStore = api.getFather()
.flatMapObservable {
Observable.fromIterable(it)
}.flatMapCompletable {
val detailInfos = it.childes.map { child ->
api.childDetailInfo(child)
.flatMapCompletable { detail -> store.store(detail) }
}
store.store(it)
.andThen(Completable.concat(detailInfos))
}
On each emit of a List of fathers, the list is flatten. The next opreator (flatMapCompletable) will take an Father. The completable will get the details of each Child with Api#childDetailInfo. The result is build by calling the API one by one. There is no concurrency happening wegen "concat". When the father is stored sucessfully, the childs will be stored as-well, when retrieved successfully. If one of the API-calls fails (e.g. network) everything fails, because the onError will be propgated to the subscriber.
Test
#Test
fun so62299778() {
val api = ApiImpl()
val store = mockk<Store>()
every { store.store(any<Father>()) } returns Completable.complete()
every { store.store(any<ChildDetailInfo>()) } returns Completable.complete()
val fathersStore = api.getFather()
.flatMapObservable {
Observable.fromIterable(it)
}.flatMapCompletable {
val detailInfos = it.childes.map { child ->
api.childDetailInfo(child)
.flatMapCompletable { detail -> store.store(detail) }
}
store.store(it)
.andThen(Completable.concat(detailInfos))
}
fathersStore.test()
.assertComplete()
verify { store.store(eq(Father(listOf(Child("1"), Child("2"))))) }
verify { store.store(eq(Father(listOf(Child("1"))))) }
verify(atLeast = 2) { store.store(eq(ChildDetailInfo("1"))) }
verify(atLeast = 1) { store.store(eq(ChildDetailInfo("2"))) }
}
Please provide next time some classes/ interfaces. When your question contains all vital information, you will get an answer quicker.
TL;DR
Can't seem to use binding to tell wrapped AVPlayer to stop — why not? The "one weird trick" from Vlad works for me, without state & binding, but why?
See Also
My question is something like this one but that poster wanted to wrap an AVPlayerViewController and I want to control playback programmatically.
This guy also wondered when updateUIView() was called.
What happens (Console logs shown below.)
With code as shown here,
The user taps "Go to Movie"
MovieView appears and the vid plays
This is because updateUIView(_:context:) is being called
The user taps "Go back Home"
HomeView reappears
Playback halts
Again updateUIView is being called.
See Console Log 1
But... remove the ### line, and
Playback continues even when the home view returns
updateUIView is called on arrival but not departure
See Console log 2
If you uncomment the %%% code (and comment out what precedes it)
You get code I thought was logically and idiomatically correct SwiftUI...
...but "it doesn't work". I.e. the vid plays on arrival but continues on departure.
See Console log 3
The code
I do use an #EnvironmentObject so there is some sharing of state going on.
Main content view (nothing controversial here):
struct HomeView: View {
#EnvironmentObject var router: ViewRouter
var body: some View {
ZStack() { // +++ Weird trick ### fails if this is Group(). Wtf?
if router.page == .home {
Button(action: { self.router.page = .movie }) {
Text("Go to Movie")
}
} else if router.page == .movie {
MovieView()
}
}
}
}
which uses one of these (still routine declarative SwiftUI):
struct MovieView: View {
#EnvironmentObject var router: ViewRouter
// #State private var isPlaying: Bool = false // %%%
var body: some View {
VStack() {
PlayerView()
// PlayerView(isPlaying: $isPlaying) // %%%
Button(action: { self.router.page = .home }) {
Text("Go back Home")
}
}.onAppear {
print("> onAppear()")
self.router.isPlayingAV = true
// self.isPlaying = true // %%%
print("< onAppear()")
}.onDisappear {
print("> onDisappear()")
self.router.isPlayingAV = false
// self.isPlaying = false // %%%
print("< onDisappear()")
}
}
}
Now we get into the AVKit-specific stuff. I use the approach described by Chris Mash.
The aforementioned PlayerView, the wrappER:
struct PlayerView: UIViewRepresentable {
#EnvironmentObject var router: ViewRouter
// #Binding var isPlaying: Bool // %%%
private var myUrl : URL? { Bundle.main.url(forResource: "myVid", withExtension: "mp4") }
func makeUIView(context: Context) -> PlayerView {
PlayerUIView(frame: .zero , url : myUrl)
}
// ### This one weird trick makes OS call updateUIView when view is disappearing.
class DummyClass { } ; let x = DummyClass()
func updateUIView(_ v: PlayerView, context: UIViewRepresentableContext<PlayerView>) {
print("> updateUIView()")
print(" router.isPlayingAV = \(router.isPlayingAV)")
// print(" isPlaying = \(isPlaying)") // %%%
// This does work. But *only* with the Dummy code ### included.
// See also +++ comment in HomeView
if router.isPlayingAV { v.player?.pause() }
else { v.player?.play() }
// This logic looks reversed, but is correct.
// If it's the other way around, vid never plays. Try it!
// if isPlaying { v?.player?.play() } // %%%
// else { v?.player?.pause() } // %%%
print("< updateUIView()")
}
}
And the wrappED UIView:
class PlayerUIView: UIView {
private let playerLayer = AVPlayerLayer()
var player: AVPlayer?
init(frame: CGRect, url: URL?) {
super.init(frame: frame)
guard let u = url else { return }
self.player = AVPlayer(url: u)
self.playerLayer.player = player
self.layer.addSublayer(playerLayer)
}
override func layoutSubviews() {
super.layoutSubviews()
playerLayer.frame = bounds
}
required init?(coder: NSCoder) { fatalError("not implemented") }
}
And of course the view router, based on the Blckbirds example
class ViewRouter : ObservableObject {
let objectWillChange = PassthroughSubject<ViewRouter, Never>()
enum Page { case home, movie }
var page = Page.home { didSet { objectWillChange.send(self) } }
// Claim: App will never play more than one vid at a time.
var isPlayingAV = false // No didSet necessary.
}
Console Logs
Console log 1 (playing stops as desired)
> updateUIView() // First call
router.isPlayingAV = false // Vid is not playing => play it.
< updateUIView()
> onAppear()
< onAppear()
> updateUIView() // Second call
router.isPlayingAV = true // Vid is playing => pause it.
< updateUIView()
> onDisappear() // After the fact, we clear
< onDisappear() // the isPlayingAV flag.
Console log 2 (weird trick disabled; playing continues)
> updateUIView() // First call
router.isPlayingAV = false
< updateUIView()
> onAppear()
< onAppear()
// No second call.
> onDisappear()
< onDisappear()
Console log 3 (attempt to use state & binding; playing continues)
> updateUIView()
isPlaying = false
< updateUIView()
> onAppear()
< onAppear()
> updateUIView()
isPlaying = true
< updateUIView()
> updateUIView()
isPlaying = true
< updateUIView()
> onDisappear()
< onDisappear()
Well... on
}.onDisappear {
print("> onDisappear()")
self.router.isPlayingAV = false
print("< onDisappear()")
}
this is called after view is removed (it is like didRemoveFromSuperview, not will...), so I don't see anything bad/wrong/unexpected in that subviews (or even it itself) is not updated (in this case updateUIView)... I would rather surprise if it would be so (why update view, which is not in view hierarchy?!).
So this
class DummyClass { } ; let x = DummyClass()
is rather some wild bug, or ... bug. Forget about it and never use such stuff in releasing products.
OK, one would now ask, how to do with this? The main issue I see here is design-originated, specifically tight-coupling of model and view in PlayerUIView and, as a result, impossibility to manage workflow. AVPlayer here is not part of view - it is model and depending on its states AVPlayerLayer draws content. Thus the solution is to tear apart those entities and manage separately: views by views, models by models.
Here is a demo of modified & simplified approach, which behaves as expected (w/o weird stuff and w/o Group/ZStack limitations), and it can be easily extended or improved (in model/viewmodel layer)
Tested with Xcode 11.2 / iOS 13.2
Complete module code (can be copy-pasted in ContentView.swift in project from template)
import SwiftUI
import Combine
import AVKit
struct MovieView: View {
#EnvironmentObject var router: ViewRouter
// just for demo, but can be interchangable/modifiable
let playerModel = PlayerViewModel(url: Bundle.main.url(forResource: "myVid", withExtension: "mp4")!)
var body: some View {
VStack() {
PlayerView(viewModel: playerModel)
Button(action: { self.router.page = .home }) {
Text("Go back Home")
}
}.onAppear {
self.playerModel.player?.play() // << changes state of player, ie model
}.onDisappear {
self.playerModel.player?.pause() // << changes state of player, ie model
}
}
}
class PlayerViewModel: ObservableObject {
#Published var player: AVPlayer? // can be changable depending on modified URL, etc.
init(url: URL) {
self.player = AVPlayer(url: url)
}
}
struct PlayerView: UIViewRepresentable { // just thing wrapper, as intended
var viewModel: PlayerViewModel
func makeUIView(context: Context) -> PlayerUIView {
PlayerUIView(frame: .zero , player: viewModel.player) // if needed viewModel can be passed completely
}
func updateUIView(_ v: PlayerUIView, context: UIViewRepresentableContext<PlayerView>) {
}
}
class ViewRouter : ObservableObject {
enum Page { case home, movie }
#Published var page = Page.home // used native publisher
}
class PlayerUIView: UIView {
private let playerLayer = AVPlayerLayer()
var player: AVPlayer?
init(frame: CGRect, player: AVPlayer?) { // player is a model so inject it here
super.init(frame: frame)
self.player = player
self.playerLayer.player = player
self.layer.addSublayer(playerLayer)
}
override func layoutSubviews() {
super.layoutSubviews()
playerLayer.frame = bounds
}
required init?(coder: NSCoder) { fatalError("not implemented") }
}
struct ContentView: View {
#EnvironmentObject var router: ViewRouter
var body: some View {
Group {
if router.page == .home {
Button(action: { self.router.page = .movie }) {
Text("Go to Movie")
}
} else if router.page == .movie {
MovieView()
}
}
}
}
I'm populating a List with a Realm Result set.
When navigating from this list it opens a new view then automatically closes that view.
Using a struct presents no issue.
Why would the second view automatically close?
I have a screen recording but cant post here.
import SwiftUI
import Combine
struct TestStruct:Identifiable{
let id = UUID()
let firstname: String
}
extension TestStruct {
static func all() -> [TestStruct]{
return[
TestStruct(firstname: "Joe"),
TestStruct(firstname: "Jane"),
TestStruct(firstname: "Johns")
]
}
}
struct TestListView: View {
let realmList = Horoscope.getHoroscopes() //Fetches from Realm
let structList = TestStruct.all()
var body: some View {
NavigationView{
// This owrks
// List(structList) { item in
// MyItemRow(itemTxt: item.firstname)
// }
//This automatically closes the view
List(realmList) { item in
MyItemRow(itemTxt: item.firstname)
}
.navigationBarTitle("Charts", displayMode: .automatic)
.navigationBarItems(trailing: EditButton())
}
}
}
struct MyItemRow: View {
var itemTxt:String
var body: some View {
NavigationLink(destination: Text("Test")) {
Text(itemTxt)
}
}
}
struct TestListView_Previews: PreviewProvider {
static var previews: some View {
TestListView()
}
}
I think the answer can be found here
In short, do not generate the id of the collection on which the ForEach iterates. It would detect a change and navigate back.
Realm object has an auto generated id property with each reference, try replacing it with a consistent id
The following solution worked for me.
The code with an issue (specifying id: \.self is the root cause since it uses the hash calculated from all objects the Stream object consists of, including the data that lies in a subarray).
...
List(streams, id: \.self) { stream in
...
The code with no issues:
...
List(streams, id: \._id) { stream in
// or even List(streams) { stream in
...
The streams is a #ObservedResults(Stream.self) var streams and the object scheme is:
final class Stream: Object, ObjectKeyIdentifiable {
#Persisted(primaryKey: true) var _id: ObjectId
#Persisted var title: String
#Persisted var subtitle: String?
#Persisted var topics = RealmSwift.List<Topic>()
// tags, etc.
}
The issue happened when I added new topic at the topics list in the first stack of the navigationView.
In Objective-C, I would normally use something like this:
static NSString *kViewTransformChanged = #"view transform changed";
// or
static const void *kViewTransformChanged = &kViewTransformChanged;
[clearContentView addObserver:self
forKeyPath:#"transform"
options:NSKeyValueObservingOptionNew
context:&kViewTransformChanged];
I have two overloaded methods to choose from to add an observer for KVO with the only difference being the context argument:
clearContentView.addObserver(observer: NSObject?, forKeyPath: String?, options: NSKeyValueObservingOptions, context: CMutableVoidPointer)
clearContentView.addObserver(observer: NSObject?, forKeyPath: String?, options: NSKeyValueObservingOptions, kvoContext: KVOContext)
With Swift not using pointers, I'm not sure how to dereference a pointer to use the first method.
If I create my own KVOContext constant for use with the second method, I wind up with it asking for this:
let test:KVOContext = KVOContext.fromVoidContext(context: CMutableVoidPointer)
EDIT: What is the difference between CMutableVoidPointer and KVOContext? Can someone give me an example how how to use them both and when I would use one over the other?
EDIT #2: A dev at Apple just posted this to the forums: KVOContext is going away; using a global reference as your context is the way to go right now.
There is now a technique officially recommended in the documentation, which is to create a private mutable variable and use its address as the context.
(Updated for Swift 3 on 2017-01-09)
// Set up non-zero-sized storage. We don't intend to mutate this variable,
// but it needs to be `var` so we can pass its address in as UnsafeMutablePointer.
private static var myContext = 0
// NOTE: `static` is not necessary if you want it to be a global variable
observee.addObserver(self, forKeyPath: …, options: [], context: &MyClass.myContext)
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey: Any]?, context: UnsafeMutableRawPointer?) {
if context == &myContext {
…
}
else {
super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)
}
}
Now that KVOContext is gone in Xcode 6 beta 3, you can do the following. Define a global (i.e. not a class property) like so:
let myContext = UnsafePointer<()>()
Add an observer:
observee.addObserver(observer, forKeyPath: …, options: nil, context: myContext)
In the observer:
override func observeValueForKeyPath(keyPath: String!, ofObject object: AnyObject!, change: [NSObject : AnyObject]!, context: UnsafePointer<()>) {
if context == myContext {
…
} else {
super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
}
}
Swift 4 - observing contentSize change on UITableViewController popover to fix incorrect size
I had been searching for an answer to change to a block based KVO because I was getting a swiftlint warning and it took me piecing quite a few different answers together to get to the right solution. Swiftlint warning:
Block Based KVO Violation: Prefer the new block based KVO API with keypaths when using Swift 3.2 or later. (block_based_kvo).
My use case was to present a popover controller attached to a button in a Nav bar in a view controller and then resize the popover once it's showing - otherwise it would be too big and not fitting the contents of the popover. The popover itself was a UITableViewController that contained static cells, and it was displayed via a Storyboard segue with style popover.
To setup the block based observer, you need the following code inside your popover UITableViewController:
// class level variable to store the statusObserver
private var statusObserver: NSKeyValueObservation?
// Create the observer inside viewWillAppear
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
statusObserver = tableView.observe(\UITableView.contentSize,
changeHandler: { [ weak self ] (theTableView, _) in self?.popoverPresentationController?.presentedViewController.preferredContentSize = theTableView.contentSize
})
}
// Don't forget to remove the observer when the popover is dismissed.
override func viewDidDisappear(_ animated: Bool) {
if let observer = statusObserver {
observer.invalidate()
statusObserver = nil
}
super.viewDidDisappear(animated)
}
I didn't need the previous value when the observer was triggered, so left out the options: [.new, .old] when creating the observer.
Update for Swift 4
Context is not required for block-based observer function and existing #keyPath() syntax is replaced with smart keypath to achieve swift type safety.
class EventOvserverDemo {
var statusObserver:NSKeyValueObservation?
var objectToObserve:UIView?
func registerAddObserver() -> Void {
statusObserver = objectToObserve?.observe(\UIView.tag, options: [.new, .old], changeHandler: {[weak self] (player, change) in
if let tag = change.newValue {
// observed changed value and do the task here on change.
}
})
}
func unregisterObserver() -> Void {
if let sObserver = statusObserver {
sObserver.invalidate()
statusObserver = nil
}
}
}
Complete example using Swift:
//
// AppDelegate.swift
// Photos-MediaFramework-swift
//
// Created by Phurg on 11/11/16.
//
// Displays URLs for all photos in Photos Library
//
// #see http://stackoverflow.com/questions/30144547/programmatic-access-to-the-photos-library-on-mac-os-x-photokit-photos-framewo
//
import Cocoa
import MediaLibrary
// For KVO: https://developer.apple.com/library/content/documentation/Swift/Conceptual/BuildingCocoaApps/AdoptingCocoaDesignPatterns.html#//apple_ref/doc/uid/TP40014216-CH7-ID12
private var mediaLibraryLoaded = 1
private var rootMediaGroupLoaded = 2
private var mediaObjectsLoaded = 3
#NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
#IBOutlet weak var window: NSWindow!
var mediaLibrary : MLMediaLibrary!
var allPhotosAlbum : MLMediaGroup!
func applicationDidFinishLaunching(_ aNotification: Notification) {
NSLog("applicationDidFinishLaunching:");
let options:[String:Any] = [
MLMediaLoadSourceTypesKey: MLMediaSourceType.image.rawValue, // Can't be Swift enum
MLMediaLoadIncludeSourcesKey: [MLMediaSourcePhotosIdentifier], // Array
]
self.mediaLibrary = MLMediaLibrary(options:options)
NSLog("applicationDidFinishLaunching: mediaLibrary=%#", self.mediaLibrary);
self.mediaLibrary.addObserver(self, forKeyPath:"mediaSources", options:[], context:&mediaLibraryLoaded)
NSLog("applicationDidFinishLaunching: added mediaSources observer");
// Force load
self.mediaLibrary.mediaSources?[MLMediaSourcePhotosIdentifier]
NSLog("applicationDidFinishLaunching: done");
}
override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
NSLog("observeValue: keyPath=%#", keyPath!)
let mediaSource:MLMediaSource = self.mediaLibrary.mediaSources![MLMediaSourcePhotosIdentifier]!
if (context == &mediaLibraryLoaded) {
NSLog("observeValue: mediaLibraryLoaded")
mediaSource.addObserver(self, forKeyPath:"rootMediaGroup", options:[], context:&rootMediaGroupLoaded)
// Force load
mediaSource.rootMediaGroup
} else if (context == &rootMediaGroupLoaded) {
NSLog("observeValue: rootMediaGroupLoaded")
let albums:MLMediaGroup = mediaSource.mediaGroup(forIdentifier:"TopLevelAlbums")!
for album in albums.childGroups! {
let albumIdentifier:String = album.attributes["identifier"] as! String
if (albumIdentifier == "allPhotosAlbum") {
self.allPhotosAlbum = album
album.addObserver(self, forKeyPath:"mediaObjects", options:[], context:&mediaObjectsLoaded)
// Force load
album.mediaObjects
}
}
} else if (context == &mediaObjectsLoaded) {
NSLog("observeValue: mediaObjectsLoaded")
let mediaObjects:[MLMediaObject] = self.allPhotosAlbum.mediaObjects!
for mediaObject in mediaObjects {
let url:URL? = mediaObject.url
// URL does not extend NSObject, so can't be passed to NSLog; use string interpolation
NSLog("%#", "\(url)")
}
}
}
}