Printed on: September 7, 2022
UPDATE FOR XCODE 14.1: This challenge seems to have been partially mounted in Xcode 14.1. Some occurences of the warning are mounted, others aren’t. On this submit I am accumulating conditions me and others run into and monitor whether or not they’re mounted 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, 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 an alternative, it serves to point out you the occasion the place I bumped into this challenge in Xcode 14, and why I imagine this challenge is a bug and never an precise challenge. 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 wish to duplicate my challenge.
Among the SwiftUI code that I have been utilizing nice for a very long time now has not too long ago began developing with this purple warning.
Initially I assumed that there was an opportunity that I used to be, in truth, doing one thing bizarre all alongside and I began chipping away at my venture till I had one thing that was sufficiently small to solely cowl a couple of traces, however nonetheless advanced sufficient to symbolize the true world.
On this submit I’ve collected some instance of the place I and different encounter this challenge, together with whether or not it has been mounted or not.
[Fixed] Purple warnings when updating an @Printed var from a Button in a Record.
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 {
Record {
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. Nonetheless, this code nonetheless throws up the purple warning. Compiling this similar venture in Xcode 13.4.1 works nice, and older Xcode 14 betas additionally do not complain.
At this level, it looks like this is likely to be a bug in Record 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 incorrect 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 would like your button to appear to be the default button fashion on iOS, you should use borderless:
Button(motion: {
dataSource.mutate()
}, label: {
Textual content("Replace property")
}).buttonStyle(.borderless)It type of appears like something besides a default Button in a Record is okay.
For these causes, I sadly can not provide you with a correct repair for this challenge. 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 are able to hopefully get this mounted, documented, or in any other case defined. I will be requesting a code stage help ticket from Apple to see if an Apple engineer can assist 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(middle: CLLocationCoordinate2D(latitude: 10.0, longitude: 0.0), span: MKCoordinateSpan(latitudeDelta: 100, longitudeDelta: 100))
var physique: some View {
VStack {
Map(coordinateRegion: $currentMapRegion, annotationItems: allFriends) { pal in
MapAnnotation(coordinate: CLLocationCoordinate2D(latitude: 0, longitude: 0)) {
Circle()
.body(width: 20, peak: 20)
.foregroundColor(.purple)
}
}
}
.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 manner 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 wish to animate to a brand new place. For instance, by doing the next:
var physique: some View {
VStack {
Map(coordinateRegion: $currentMapRegion, annotationItems: allFriends) { pal in
MapAnnotation(coordinate: CLLocationCoordinate2D(latitude: pal.cityLatitude ?? 0, longitude: pal.cityLongitude ?? 0)) {
Circle()
.body(width: 20, peak: 20)
.foregroundColor(.purple)
}
}
}
.ignoresSafeArea()
.onAppear {
DispatchQueue.major.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 ultimately strikes the map to a brand new place. The animation may be triggered by a Button or actually the rest; how we set off the animation is not the purpose.
When the animation runs, we see tons and many warnings within the console (187 for me…) and so they all say [SwiftUI] Publishing modifications from inside view updates just isn't allowed, this can trigger undefined conduct..
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 a bit of:
Map(coordinateRegion: Binding(get: {
self.currentMapRegion
}, set: { newValue, _ in
print("(Date()) assigning new worth (newValue)")
self.currentMapRegion = newValue
}), annotationItems: allFriends) { pal in
MapAnnotation(coordinate: CLLocationCoordinate2D(latitude: pal.cityLatitude ?? 0, longitude: pal.cityLongitude ?? 0)) {
Circle()
.body(width: 20, peak: 20)
.foregroundColor(.purple)
}
}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 end result:
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 just isn't allowed, this can trigger undefined conduct.
2022-10-26 10:38:39.169692+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates just isn't allowed, this can trigger undefined conduct.
2022-10-26 10:38:39.169874+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates just isn't allowed, this can trigger undefined conduct.
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 just isn't allowed, this can trigger undefined conduct.
2022-10-26 10:38:39.186603+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates just isn't allowed, this can trigger undefined conduct.
2022-10-26 10:38:39.186785+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates just isn't allowed, this can trigger undefined conduct.
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 just isn't allowed, this can trigger undefined conduct.
2022-10-26 10:38:39.200369+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates just isn't allowed, this can trigger undefined conduct.
2022-10-26 10:38:39.200681+0200 MapBug[10097:899178] [SwiftUI] Publishing modifications from inside view updates just isn't allowed, this can trigger undefined conduct.That is only a small a part of the output in fact however we are able to clearly see that the print from the customized Binding is executed in between warnings.
I can solely conclude that this must be some challenge in Map that we can not remedy ourselves. You may have the ability to tweak the customized binding a bunch to throttle how typically it truly updates the underlying @State however I am unsure that is what we should always need…
If you happen to’re seeing this challenge too, you possibly can reference FB11720091 in suggestions that you simply file with Apple.
Large due to Tim Isenman for sending me this pattern.
