Revealed on: September 7, 2022
UPDATE FOR XCODE 14.1: This difficulty seems to have been partially fastened in Xcode 14.1. Some occurences of the warning are fastened, others aren’t. On this submit I am gathering conditions me and others run into and observe whether or not they’re fastened or not. If in case you have one other pattern that you just suppose is analogous, please ship a pattern of your code on Twitter as a Github Gist.
Pricey reader, in case you’ve discovered this web page you are in all probability encountering the error from the submit title. Let me begin by saying this submit does not give you a fast repair. As a substitute, it serves to point out you the occasion the place I bumped into this difficulty in Xcode 14, and why I consider this difficulty is a bug and never an precise difficulty. I’ve final examined this with Xcode 14.0’s Launch Candidate. I’ve filed suggestions with Apple, the suggestions quantity is
FB11278036in case you need to duplicate my difficulty.
A few of the SwiftUI code that I have been utilizing nice for a very long time now has lately began developing with this purple warning.
Initially I believed that there was an opportunity that I used to be, in reality, doing one thing bizarre all alongside and I began chipping away at my mission till I had one thing that was sufficiently small to solely cowl a couple of strains, however nonetheless complicated sufficient to symbolize the actual world.
On this submit I’ve collected some instance of the place I and different encounter this difficulty, together with whether or not it has been fastened or not.
[Fixed] Purple warnings when updating an @Revealed var from a Button in a Listing.
In my case, the problem occurred with the next code:
class SampleObject: ObservableObject {
@Revealed var publishedProp = 1337
func mutate() {
publishedProp = Int.random(in: 0...50)
}
}
struct CellView: View {
@ObservedObject var dataSource: SampleObject
var physique: some View {
VStack {
Button(motion: {
dataSource.mutate()
}, label: {
Textual content("Replace property")
})
Textual content("(dataSource.publishedProp)")
}
}
}
struct ContentView: View {
@StateObject var dataSource = SampleObject()
var physique: some View {
Listing {
CellView(dataSource: dataSource)
}
}
}This code actually does nothing outrageous or bizarre. A faucet on a button will merely mutate an @Revealed property, and I count on the listing to replace. Nothing fancy. Nonetheless, this code nonetheless throws up the purple warning. Compiling this identical mission in Xcode 13.4.1 works nice, and older Xcode 14 betas additionally do not complain.
At this level, it looks as if this may be a bug in Listing particularly as a result of altering the listing to a VStack or LazyVStack in a ScrollView doesn’t give me the identical warning. This tells me that there’s nothing essentially improper with the setup above.
One other factor that appears to work round this warning is to alter the kind of button that triggers the motion. For instance, utilizing a bordered button as proven under additionally runs with out the warning:
Button(motion: {
dataSource.mutate()
}, label: {
Textual content("Replace property")
}).buttonStyle(.bordered)Or if you’d like your button to appear like the default button model on iOS, you need to use borderless:
Button(motion: {
dataSource.mutate()
}, label: {
Textual content("Replace property")
}).buttonStyle(.borderless)It type of appears to be like like something besides a default Button in a Listing is ok.
For these causes, I sadly can’t provide you with a correct repair for this difficulty. The issues I discussed are all workarounds IMO as a result of the unique code ought to work. All I can say is please file a suggestions ticket with Apple so we will hopefully get this fastened, documented, or in any other case defined. I will be requesting a code degree assist ticket from Apple to see if an Apple engineer will help me determine this out.
Animating a map’s place in SwiftUI
A Map in SwiftUI is offered utilizing the next code:
struct ContentView: View {
@State var currentMapRegion = MKCoordinateRegion(middle: CLLocationCoordinate2D(latitude: 10.0, longitude: 0.0), span: MKCoordinateSpan(latitudeDelta: 100, longitudeDelta: 100))
var physique: some View {
VStack {
Map(coordinateRegion: $currentMapRegion, annotationItems: allFriends) { good friend in
MapAnnotation(coordinate: CLLocationCoordinate2D(latitude: 0, longitude: 0)) {
Circle()
.body(width: 20, top: 20)
.foregroundColor(.pink)
}
}
}
.ignoresSafeArea()
}
}Discover how the Map takes a Binding for its coordinateRegion. Which means that each time the map modifications what we’re taking a look at, our @State can replace and the opposite method round. We will assign a brand new MKCoordinateRegion to our @State property and the Map will replace to point out the brand new location. It does this with out animating the change. So as an instance we do need to animate to a brand new place. For instance, by doing the next:
var physique: some View {
VStack {
Map(coordinateRegion: $currentMapRegion, annotationItems: allFriends) { good friend in
MapAnnotation(coordinate: CLLocationCoordinate2D(latitude: good friend.cityLatitude ?? 0, longitude: good friend.cityLongitude ?? 0)) {
Circle()
.body(width: 20, top: 20)
.foregroundColor(.pink)
}
}
}
.ignoresSafeArea()
.onAppear {
DispatchQueue.essential.asyncAfter(deadline: .now() + 3) {
withAnimation {
currentMapRegion = MKCoordinateRegion(middle: CLLocationCoordinate2D(latitude: 80, longitude: 80),
span: MKCoordinateSpan(latitudeDelta: 100, longitudeDelta: 100))
}
}
}
}This code applies some delay after which finally strikes the map to a brand new place. The animation is also triggered by a Button or actually the rest; how we set off the animation is not the purpose.
When the animation runs, we see heaps and plenty of warnings within the console (187 for me…) and so they all say [SwiftUI] Publishing modifications from inside view updates shouldn't be allowed, this may trigger undefined habits..
We’re clearly simply updating our currentMapRegion simply as soon as, and placing print statements within the onAppear tells us that the onAppear and the withAnimation block are all known as precisely as soon as.
I suspected that the Map itself was updating its binding to animate from one place to the subsequent so I modified the Map setup code just a little:
Map(coordinateRegion: Binding(get: {
self.currentMapRegion
}, set: { newValue, _ in
print("(Date()) assigning new worth (newValue)")
self.currentMapRegion = newValue
}), annotationItems: allFriends) { good friend in
MapAnnotation(coordinate: CLLocationCoordinate2D(latitude: good friend.cityLatitude ?? 0, longitude: good friend.cityLongitude ?? 0)) {
Circle()
.body(width: 20, top: 20)
.foregroundColor(.pink)
}
}As a substitute of straight binding to the currentMapRegion property, I made a customized occasion of Binding that enables me to intercept any write operations to see what number of happen and why. Working the code with this in place, yields an fascinating consequence:
2022-10-26 08:38:39 +0000 assigning new worth MKCoordinateRegion(middle: __C.CLLocationCoordinate2D(latitude: 62.973218679210305, longitude: 79.83448028564462), span: __C.MKCoordinateSpan(latitudeDelta: 89.49072082474844, longitudeDelta: 89.0964063502501))
2022-10-26 10:38:39.169480+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates shouldn't be allowed, this may trigger undefined habits.
2022-10-26 10:38:39.169692+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates shouldn't be allowed, this may trigger undefined habits.
2022-10-26 10:38:39.169874+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates shouldn't be allowed, this may trigger undefined habits.
2022-10-26 08:38:39 +0000 assigning new worth MKCoordinateRegion(middle: __C.CLLocationCoordinate2D(latitude: 63.02444217894995, longitude: 79.96021270751967), span: __C.MKCoordinateSpan(latitudeDelta: 89.39019889305074, longitudeDelta: 89.09640635025013))
2022-10-26 10:38:39.186402+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates shouldn't be allowed, this may trigger undefined habits.
2022-10-26 10:38:39.186603+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates shouldn't be allowed, this may trigger undefined habits.
2022-10-26 10:38:39.186785+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates shouldn't be allowed, this may trigger undefined habits.
2022-10-26 08:38:39 +0000 assigning new worth MKCoordinateRegion(middle: __C.CLLocationCoordinate2D(latitude: 63.04063284402105, longitude: 80.00000000000011), span: __C.MKCoordinateSpan(latitudeDelta: 89.35838016069978, longitudeDelta: 89.0964063502501))
2022-10-26 10:38:39.200000+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates shouldn't be allowed, this may trigger undefined habits.
2022-10-26 10:38:39.200369+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates shouldn't be allowed, this may trigger undefined habits.
2022-10-26 10:38:39.200681+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates shouldn't be allowed, this may trigger undefined habits.That is only a small a part of the output in fact however we will clearly see that the print from the customized Binding is executed in between warnings.
I can solely conclude that this must be some difficulty in Map that we can’t remedy ourselves. You would possibly be capable of tweak the customized binding a bunch to throttle how typically it truly updates the underlying @State however I am undecided that is what we should always need…
In the event you’re seeing this difficulty too, you’ll be able to reference FB11720091 in suggestions that you just file with Apple.
Large because of Tim Isenman for sending me this pattern.
