Printed on: September 7, 2022
UPDATE FOR XCODE 14.1: This subject seems to have been partially fastened in Xcode 14.1. Some occurences of the warning are fastened, others aren’t. On this publish I am amassing conditions me and others run into and observe whether or not they’re fastened or not. In case you have one other pattern that you simply suppose is comparable, please ship a pattern of your code on Twitter as a Github Gist.
Expensive reader, when you’ve discovered this web page you are in all probability encountering the error from the publish title. Let me begin by saying this publish does not give you a fast repair. As an alternative, it serves to point out you the occasion the place I bumped into this subject in Xcode 14, and why I imagine this subject is a bug and never an precise subject. 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 subject.
A number of the SwiftUI code that I have been utilizing high-quality for a very long time now has just lately began developing with this purple warning.
Initially I assumed 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 just a few traces, however nonetheless advanced sufficient to signify the actual world.
On this publish I’ve collected some instance of the place I and different encounter this subject, together with whether or not it has been fastened or not.
[Fixed] Purple warnings when updating an @Printed var from a Button in a Checklist.
In my case, the problem occurred with the next code:
class SampleObject: ObservableObject {
@Printed 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 {
Checklist {
CellView(dataSource: dataSource)
}
}
}This code actually does nothing outrageous or bizarre. A faucet on a button will merely mutate an @Printed property, and I anticipate the checklist to replace. Nothing fancy. Nevertheless, this code nonetheless throws up the purple warning. Compiling this identical mission in Xcode 13.4.1 works high-quality, and older Xcode 14 betas additionally do not complain.
At this level, it looks like this is perhaps a bug in Checklist particularly as a result of altering the checklist to a VStack or LazyVStack in a ScrollView doesn’t give me the identical warning. This tells me that there’s nothing basically unsuitable 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 beneath additionally runs with out the warning:
Button(motion: {
dataSource.mutate()
}, label: {
Textual content("Replace property")
}).buttonStyle(.bordered)Or in order for you your button to seem like the default button fashion on iOS, you need to use borderless:
Button(motion: {
dataSource.mutate()
}, label: {
Textual content("Replace property")
}).buttonStyle(.borderless)It form of appears like something besides a default Button in a Checklist is ok.
For these causes, I sadly can not offer you a correct repair for this subject. 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 stage help ticket from Apple to see if an Apple engineer might help me determine this out.
Animating a map’s place in SwiftUI
A Map in SwiftUI is introduced utilizing the next code:
struct ContentView: View {
@State var currentMapRegion = MKCoordinateRegion(heart: CLLocationCoordinate2D(latitude: 10.0, longitude: 0.0), span: MKCoordinateSpan(latitudeDelta: 100, longitudeDelta: 100))
var physique: some View {
VStack {
Map(coordinateRegion: $currentMapRegion, annotationItems: allFriends) { buddy 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 every time the map modifications what we’re taking a look at, our @State can replace and the opposite approach 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 to illustrate 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) { buddy in
MapAnnotation(coordinate: CLLocationCoordinate2D(latitude: buddy.cityLatitude ?? 0, longitude: buddy.cityLongitude ?? 0)) {
Circle()
.body(width: 20, top: 20)
.foregroundColor(.pink)
}
}
}
.ignoresSafeArea()
.onAppear {
DispatchQueue.most important.asyncAfter(deadline: .now() + 3) {
withAnimation {
currentMapRegion = MKCoordinateRegion(heart: 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 may be triggered by a Button or actually anything; how we set off the animation is not the purpose.
When the animation runs, we see heaps and many warnings within the console (187 for me…) and so they all say [SwiftUI] Publishing modifications from inside view updates will not be allowed, this can 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) { buddy in
MapAnnotation(coordinate: CLLocationCoordinate2D(latitude: buddy.cityLatitude ?? 0, longitude: buddy.cityLongitude ?? 0)) {
Circle()
.body(width: 20, top: 20)
.foregroundColor(.pink)
}
}As an alternative of immediately 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 attention-grabbing outcome:
2022-10-26 08:38:39 +0000 assigning new worth MKCoordinateRegion(heart: __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 will not be allowed, this can trigger undefined habits.
2022-10-26 10:38:39.169692+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates will not be allowed, this can trigger undefined habits.
2022-10-26 10:38:39.169874+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates will not be allowed, this can trigger undefined habits.
2022-10-26 08:38:39 +0000 assigning new worth MKCoordinateRegion(heart: __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 will not be allowed, this can trigger undefined habits.
2022-10-26 10:38:39.186603+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates will not be allowed, this can trigger undefined habits.
2022-10-26 10:38:39.186785+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates will not be allowed, this can trigger undefined habits.
2022-10-26 08:38:39 +0000 assigning new worth MKCoordinateRegion(heart: __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 will not be allowed, this can trigger undefined habits.
2022-10-26 10:38:39.200369+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates will not be allowed, this can trigger undefined habits.
2022-10-26 10:38:39.200681+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates will not be allowed, this can 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 subject in Map that we can not remedy ourselves. You would possibly be capable of tweak the customized binding a bunch to throttle how usually it really updates the underlying @State however I am unsure that is what we must always need…
Should you’re seeing this subject too, you’ll be able to reference FB11720091 in suggestions that you simply file with Apple.
Large due to Tim Isenman for sending me this pattern.