Whereas testing on simulators, I’ve hit a problem the place ViewThatFits seems to have a threading challenge. This will trigger warnings or a crash.
The surroundings is the next:
- Xcode 26.0 beta 5
- Swift 6 with strict concurrency checking
- minimal deployment goal iOS 17.0
- debug construct configuration
- iPhone 16 simulator operating iOS 18.5 (causes crash)
- iPhone 15 simulator operating iOS 17.5 (causes warnings)
The next code can be utilized to breed the issue when operating with the next textual content dimension:
struct ContentView: View {
let item1 = "The fast brown fox jumps over the lazy canine."
let item2 = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua."
@State non-public var isExpanded = false
enum LayoutHint {
case regular
case spaceIsTight
case scrolling
}
non-public func itemList(gadgets: [String], trace: LayoutHint) -> some View {
VStack(alignment: .main, spacing: 9) {
ForEach(Array(gadgets.enumerated()), id: .offset) { _, textual content in
Textual content(textual content)
.font(.footnote)
}
}
.body(maxWidth: .infinity, alignment: .main)
.fixedSize(horizontal: false, vertical: true)
}
non-public func expandedExplanation(gadgets: [String]) -> some View {
ViewThatFits(in: .vertical) {
// If any of those 3 views are commented out, it really works
itemList(gadgets: gadgets, trace: .regular)
itemList(gadgets: gadgets, trace: .spaceIsTight)
ScrollView {
itemList(gadgets: gadgets, trace: .scrolling)
}
}
}
non-public var chevronUp: some View {
Picture(systemName: "chevron.compact.up")
.imageScale(.medium)
.font(.title)
.fontWeight(.semibold)
.foregroundStyle(.grey)
// If vertical padding is added, it really works
// .padding(.vertical, 10)
.body(maxWidth: .infinity)
}
non-public var expandedContent: some View {
VStack(alignment: .main, spacing: 20) {
expandedExplanation(gadgets: [item1, item2])
// If chevronUp is commented out, it really works
chevronUp
}
.padding()
}
non-public var collapsedContent: some View {
Textual content("Present expanded")
.foregroundStyle(Shade(.hyperlink))
.padding()
.body(maxWidth: .infinity)
}
var physique: some View {
ZStack(alignment: .high) {
if isExpanded {
expandedContent
} else {
collapsedContent
}
}
.clipped()
.contentShape(.rect)
.background {
UnevenRoundedRectangle(
topLeadingRadius: 0,
bottomLeadingRadius: 20,
bottomTrailingRadius: 20,
topTrailingRadius: 0
)
.fill(Shade(.systemGray6))
.ignoresSafeArea(edges: .high)
}
.onTapGesture {
withAnimation(.easeInOut(period: 0.25)) {
isExpanded.toggle()
}
}
.body(maxHeight: .infinity, alignment: .high)
}
}
Right here is the way it ought to look when the highest part is expanded (notice the textual content dimension):
The crash that occurs when operating on the iPhone 16 simulator with iOS 18.5 is as follows:
#0 0x0000000102506e28 in _dispatch_assert_queue_fail () #1 0x000000010253c388 in dispatch_assert_queue$V2.chilly.1 () #2 0x0000000102506db0 in dispatch_assert_queue () #3 0x0000000249df246c in swift_task_isCurrentExecutorWithFlagsImpl () #4 0x0000000102e80504 in closure #1 in closure #1 in ContentView.itemList(gadgets:trace:) () #5 0x0000000102e807d4 in thunk for @escaping @callee_guaranteed (@unowned Int, @assured String) -> (@owned Textual content) () #6 0x00000001d4c8cd24 in closure #1 () -> τ_0_2 in SwiftUI.ForEachState.merchandise(at: τ_0_0.Index, offset: Swift.Int) -> SwiftUI.ForEachState.Merchandise () #7 0x00000001d4c94dac in partial apply forwarder for closure #1 () -> τ_0_2 in SwiftUI.ForEachState.merchandise(at: τ_0_0.Index, offset: Swift.Int) -> SwiftUI.ForEachState.Merchandise () #8 0x00000001d4a7004c in closure #1 (Swift.UnsafeMutablePointer>) throws -> τ_0_0 in SwiftUI._withObservation(do: () throws -> τ_0_0) throws -> (worth: τ_0_0, accessList: Swift.Optionally available) () #9 0x00000001d473a6d8 in partial apply forwarder for closure #1 (Swift.UnsafeMutablePointer>) throws -> τ_0_0 in SwiftUI._withObservation(do: () throws -> τ_0_0) throws -> (worth: τ_0_0, accessList: Swift.Optionally available) () #10 0x00000001d48c9288 in withUnsafePointer () #11 0x00000001d4c8c160 in merchandise () #12 0x00000001d4c8e24c in forEachItem () #13 0x00000001d4c94b38 in perform signature specialization of SwiftUI.ForEachList.applyNodes(from: inout Swift.Int, model: SwiftUI._ViewList_IteratorStyle, checklist: Swift.Optionally available>, rework: inout SwiftUI._ViewList_SublistTransform, to: (inout Swift.Int, SwiftUI._ViewList_IteratorStyle, SwiftUI._ViewList_Node, inout SwiftUI._ViewList_SublistTransform) -> Swift.Bool) -> Swift.Bool () #14 0x00000001d4c92ec8 in protocol witness for SwiftUI.ViewList.applyNodes(from: inout Swift.Int, model: SwiftUI._ViewList_IteratorStyle, checklist: Swift.Optionally available>, rework: inout SwiftUI._ViewList_SublistTransform, to: (inout Swift.Int, SwiftUI._ViewList_IteratorStyle, SwiftUI._ViewList_Node, inout SwiftUI._ViewList_SublistTransform) -> Swift.Bool) -> Swift.Bool in conformance SwiftUI.ForEachList : SwiftUI.ViewList in SwiftUI () #15 0x00000001d49a8374 in applySublists () #16 0x00000001d49a501c in applySublists () #17 0x00000001d460d09c in generic specialization of SwiftUI.DynamicContainerInfo.updateItems(disableTransitions: Swift.Bool) -> (modified: Swift.Bool, hasDepth: Swift.Bool) () #18 0x00000001d460c258 in generic specialization of SwiftUI.DynamicContainerInfo.updateValue() -> () () #19 0x00000001d462b764 in generic specialization > of implicit closure #1 (Swift.UnsafeMutableRawPointer, __C.AGAttribute) -> () in closure #1 () -> (Swift.UnsafeMutableRawPointer, __C.AGAttribute) -> () in closure #1 (Swift.UnsafePointer) -> AttributeGraph.Attribute in AttributeGraph.Attribute.init(τ_1_0) -> AttributeGraph.Attribute () #20 0x00000001c00ca438 in AG::Graph::UpdateStack::replace () #21 0x00000001c00cac04 in AG::Graph::update_attribute () #22 0x00000001c00d24dc in AG::Graph::input_value_ref_slow () #23 0x00000001c00e8054 in AGGraphGetValue () #24 0x00000001d496010c in SwiftUI.DynamicLayoutComputer.containerInfo.getter : Swift.Optionally available () #25 0x00000001d4960248 in updateValue () #26 0x00000001d4947d58 in partial apply forwarder for implicit closure #1 (Swift.UnsafeMutableRawPointer, __C.AGAttribute) -> () in closure #1 () -> (Swift.UnsafeMutableRawPointer, __C.AGAttribute) -> () in closure #1 (Swift.UnsafePointer) -> AttributeGraph.Attribute in AttributeGraph.Attribute.init(τ_1_0) -> AttributeGraph.Attribute () #27 0x00000001c00ca438 in AG::Graph::UpdateStack::replace () #28 0x00000001c00cac04 in AG::Graph::update_attribute () #29 0x00000001c00d22f0 in AG::Graph::input_value_ref_slow () #30 0x00000001c00e7e14 in AGGraphGetInputValue () #31 0x00000001d47d1904 in dimension () #32 0x00000001d4aab49c in sizeThatFits () #33 0x00000001d4aabe74 in protocol witness for SwiftUI.UnaryLayout.sizeThatFits(in: SwiftUI._ProposedSize, context: SwiftUI.SizeAndSpacingContext, little one: SwiftUI.LayoutProxy) -> __C.CGSize in conformance SwiftUI._FlexFrameLayout : SwiftUI.UnaryLayout in SwiftUI () #34 0x00000001d4934fcc in merged SwiftUI.UnaryLayoutEngine.sizeThatFits(SwiftUI._ProposedSize) -> __C.CGSize () #35 0x00000001d4934cf4 in protocol witness for SwiftUI.LayoutEngine.sizeThatFits(SwiftUI._ProposedSize) -> __C.CGSize in conformance SwiftUI.UnaryLayoutEngine : SwiftUI.LayoutEngine in SwiftUI () #36 0x00000001d4b700ac in sizeThatFits () #37 0x00000001d47d1970 in dimension () #38 0x00000001d4664b3c in protocol witness for SwiftUI.UnaryLayout.sizeThatFits(in: SwiftUI._ProposedSize, context: SwiftUI.SizeAndSpacingContext, little one: SwiftUI.LayoutProxy) -> __C.CGSize in conformance SwiftUI._FixedSizeLayout : SwiftUI.UnaryLayout in SwiftUI () #39 0x00000001d4934fcc in merged SwiftUI.UnaryLayoutEngine.sizeThatFits(SwiftUI._ProposedSize) -> __C.CGSize () #40 0x00000001d4934cf4 in protocol witness for SwiftUI.LayoutEngine.sizeThatFits(SwiftUI._ProposedSize) -> __C.CGSize in conformance SwiftUI.UnaryLayoutEngine : SwiftUI.LayoutEngine in SwiftUI () #41 0x00000001d4b700ac in sizeThatFits () #42 0x00000001d4b6ee60 in sizeThatFits () #43 0x00000001d3b4e35c in closure #1 (SwiftUI._ViewOutputs, Swift.Bool) -> Swift.Bool in closure #1 () -> () in SwiftUI.SizeFittingLayoutComputer.Engine.explicitAlignment(_: SwiftUI.AlignmentKey, at: SwiftUI.ViewSize) -> Swift.Optionally available () #44 0x00000001d3b4cfec in closure #1 (SwiftUI._ViewList_Sublist) -> Swift.Bool in SwiftUI.SizeFittingState.applyChildren(selectLast: Swift.Bool, to: (SwiftUI._ViewOutputs, Swift.Bool) -> Swift.Bool) -> () () #45 0x00000001d49a7640 in applySublists () #46 0x00000001d49b09e8 in merged partial apply forwarder for closure #1 (inout Swift.Int, SwiftUI._ViewList_IteratorStyle, SwiftUI._ViewList_Node, inout SwiftUI._ViewList_SublistTransform) -> Swift.Bool in SwiftUI._ViewList_Node.applySublists(from: inout Swift.Int, model: SwiftUI._ViewList_IteratorStyle, rework: inout SwiftUI._ViewList_SublistTransform, to: (SwiftUI._ViewList_Sublist) -> Swift.Bool) -> Swift.Bool () #47 0x00000001d49abddc in applyNodes () #48 0x00000001d49a8374 in applySublists () #49 0x00000001d49a501c in applySublists () #50 0x00000001d3b4c190 in applyChildren () #51 0x00000001d3b4e144 in closure #1 () -> () in SwiftUI.SizeFittingLayoutComputer.Engine.explicitAlignment(_: SwiftUI.AlignmentKey, at: SwiftUI.ViewSize) -> Swift.Optionally available () #52 0x00000001c00cafb0 in AG::Graph::with_update () #53 0x00000001d3b4e524 in protocol witness for SwiftUI.LayoutEngine.explicitAlignment(_: SwiftUI.AlignmentKey, at: SwiftUI.ViewSize) -> Swift.Optionally available in conformance SwiftUI.SizeFittingLayoutComputer.Engine : SwiftUI.LayoutEngine in SwiftUI () #54 0x00000001d4b70194 in explicitAlignment () #55 0x00000001d4c16cfc in perform signature specialization Swift.Optionally available in SwiftUI.StackLayout.(UnmanagedImplementation in _00690F480F8D293143B214DBE6D72CD0).placeChildren(in: SwiftUI.ProposedViewSize) -> (), Argument Varieties : [Swift.Optional]> of SwiftUI.StackLayout.UnmanagedImplementation.sizeChildrenGenerallyWithConcreteMajorProposal(in: SwiftUI.ProposedViewSize, minorProposalForChild: (SwiftUI.StackLayout.Little one) -> Swift.Optionally available) -> () () #56 0x00000001d4c1779c in perform signature specialization Swift.Optionally available in SwiftUI.StackLayout.(UnmanagedImplementation in _00690F480F8D293143B214DBE6D72CD0).placeChildren(in: SwiftUI.ProposedViewSize) -> (), Argument Varieties : [Swift.Optional]> of SwiftUI.StackLayout.UnmanagedImplementation.placeChildren1(in: SwiftUI.ProposedViewSize, minorProposalForChild: (SwiftUI.StackLayout.Little one) -> Swift.Optionally available) -> () () #57 0x00000001d4c15fb4 in placeChildren () #58 0x00000001d4c15c84 in explicitAlignment () #59 0x00000001d4c14664 in explicitAlignment () #60 0x00000001d47a46a8 in merged protocol witness for SwiftUI.Format.explicitAlignment(of: SwiftUI.HorizontalAlignment, in: __C.CGRect, proposal: SwiftUI.ProposedViewSize, subviews: SwiftUI.LayoutSubviews, cache: inout τ_0_0.Cache) -> Swift.Optionally available in conformance SwiftUI._VStackLayout : SwiftUI.Format in SwiftUI () #61 0x00000001d496875c in closure #1 (Swift.UnsafeMutablePointer) -> Swift.Optionally available in closure #1 (Swift.UnsafeMutablePointer>) -> Swift.Optionally available in SwiftUI.ViewLayoutEngine.explicitAlignment(_: SwiftUI.AlignmentKey, at: SwiftUI.ViewSize) -> Swift.Optionally available () #62 0x00000001d49684c4 in closure #1 (Swift.UnsafeMutablePointer>) -> Swift.Optionally available in SwiftUI.ViewLayoutEngine.explicitAlignment(_: SwiftUI.AlignmentKey, at: SwiftUI.ViewSize) -> Swift.Optionally available () #63 0x00000001d496ab24 in partial apply forwarder for closure #1 (Swift.UnsafeMutablePointer>) -> Swift.Optionally available in SwiftUI.ViewLayoutEngine.explicitAlignment(_: SwiftUI.AlignmentKey, at: SwiftUI.ViewSize) -> Swift.Optionally available () #64 0x00000001d48c9288 in withUnsafePointer () #65 0x00000001d496837c in explicitAlignment () #66 0x00000001d4968df0 in protocol witness for SwiftUI.LayoutEngine.explicitAlignment(_: SwiftUI.AlignmentKey, at: SwiftUI.ViewSize) -> Swift.Optionally available in conformance SwiftUI.ViewLayoutEngine : SwiftUI.LayoutEngine in SwiftUI () #67 0x00000001d4b70194 in explicitAlignment () #68 0x00000001d47d26f0 in explicitAlignment () #69 0x00000001d4934c68 in explicitAlignment () #70 0x00000001d4934d08 in protocol witness for SwiftUI.LayoutEngine.explicitAlignment(_: SwiftUI.AlignmentKey, at: SwiftUI.ViewSize) -> Swift.Optionally available in conformance SwiftUI.UnaryLayoutEngine : SwiftUI.LayoutEngine in SwiftUI () #71 0x00000001d4b70194 in explicitAlignment () #72 0x00000001d4663040 in SwiftUI.ViewDimensions.subscript.getter : (SwiftUI.AlignmentKey) -> CoreGraphics.CGFloat () #73 0x00000001d4569c74 in perform signature specialization __C.CGPoint in SwiftUI._ZStackLayout.placeSubviews(in: __C.CGRect, proposal: SwiftUI.ProposedViewSize, subviews: SwiftUI.LayoutSubviews, cache: inout ()) -> (), Argument Varieties : [SwiftUI._ZStackLayout]> of generic specialization , SwiftUI.ViewDimensions>, __C.CGPoint> of Swift.Sequence.cut back(τ_1_0, (τ_1_0, τ_0_0.Aspect) throws -> τ_1_0) throws -> τ_1_0 () #74 0x00000001d458d844 in perform signature specialization of SwiftUI._ZStackLayout.placeSubviews(in: __C.CGRect, proposal: SwiftUI.ProposedViewSize, subviews: SwiftUI.LayoutSubviews, cache: inout ()) -> () () #75 0x00000001d4967e0c in closure #1 (Swift.UnsafeMutablePointer) -> () in SwiftUI.ViewLayoutEngine.childGeometries(at: SwiftUI.ViewSize, origin: __C.CGPoint) -> Swift.Array () #76 0x00000001d4967bb8 in childGeometries () #77 0x00000001d4968aa4 in static SwiftUI.ViewLayoutEngine.defaultAlignment(_: SwiftUI.AlignmentKey, dimension: SwiftUI.ViewSize, information: Swift.UnsafeMutableRawPointer) -> Swift.Optionally available () #78 0x00000001d4968e10 in protocol witness for static SwiftUI.DefaultAlignmentFunction.defaultAlignment(_: SwiftUI.AlignmentKey, dimension: SwiftUI.ViewSize, information: Swift.UnsafeMutableRawPointer) -> Swift.Optionally available in conformance SwiftUI.ViewLayoutEngine : SwiftUI.DefaultAlignmentFunction in SwiftUI () #79 0x00000001d495287c in merged protocol witness for SwiftUI.Format.explicitAlignment(of: SwiftUI.HorizontalAlignment, in: __C.CGRect, proposal: SwiftUI.ProposedViewSize, subviews: SwiftUI.LayoutSubviews, cache: inout τ_0_0.Cache) -> Swift.Optionally available in conformance SwiftUI._ZStackLayout : SwiftUI.Format in SwiftUI () #80 0x00000001d496875c in closure #1 (Swift.UnsafeMutablePointer) -> Swift.Optionally available in closure #1 (Swift.UnsafeMutablePointer>) -> Swift.Optionally available in SwiftUI.ViewLayoutEngine.explicitAlignment(_: SwiftUI.AlignmentKey, at: SwiftUI.ViewSize) -> Swift.Optionally available () #81 0x00000001d49684c4 in closure #1 (Swift.UnsafeMutablePointer>) -> Swift.Optionally available in SwiftUI.ViewLayoutEngine.explicitAlignment(_: SwiftUI.AlignmentKey, at: SwiftUI.ViewSize) -> Swift.Optionally available () #82 0x00000001d496ab24 in partial apply forwarder for closure #1 (Swift.UnsafeMutablePointer>) -> Swift.Optionally available in SwiftUI.ViewLayoutEngine.explicitAlignment(_: SwiftUI.AlignmentKey, at: SwiftUI.ViewSize) -> Swift.Optionally available () #83 0x00000001d48c9288 in withUnsafePointer () #84 0x00000001d496837c in explicitAlignment () #85 0x00000001d4968df0 in protocol witness for SwiftUI.LayoutEngine.explicitAlignment(_: SwiftUI.AlignmentKey, at: SwiftUI.ViewSize) -> Swift.Optionally available in conformance SwiftUI.ViewLayoutEngine : SwiftUI.LayoutEngine in SwiftUI () #86 0x00000001d4b70194 in explicitAlignment () #87 0x00000001d4663040 in SwiftUI.ViewDimensions.subscript.getter : (SwiftUI.AlignmentKey) -> CoreGraphics.CGFloat () #88 0x00000001d4aaa9f0 in generic specialization of SwiftUI.FrameLayoutCommon.commonPlacement(of: SwiftUI.LayoutProxy, in: SwiftUI.PlacementContext, childProposal: SwiftUI._ProposedSize) -> SwiftUI._Placement () #89 0x00000001d49336cc in generic specialization of SwiftUI.UnaryLayoutEngine.childPlacement(at: SwiftUI.ViewSize) -> SwiftUI._Placement () #90 0x00000001d4947910 in partial apply forwarder for generic specialization of closure #1 (inout SwiftUI.UnaryLayoutEngine) -> SwiftUI._Placement in SwiftUI.UnaryChildGeometry.worth.getter : SwiftUI.ViewGeometry () #91 0x00000001d48c33f0 in partial apply forwarder for generic specialization , SwiftUI._Placement> of closure #1 (inout τ_0_0) -> τ_0_1 in SwiftUI.LayoutComputer.withMutableEngine(kind: τ_0_0.Kind, do: (inout τ_0_0) -> τ_0_1) -> τ_0_1 () #92 0x00000001d4b70d10 in partial apply forwarder for closure #1 (Swift.UnsafeMutablePointer) -> τ_1_1 in SwiftUI.LayoutEngineBox.mutateEngine(as: τ_1_0.Kind, do: (inout τ_1_0) -> τ_1_1) -> τ_1_1 () #93 0x00000001d48c9288 in withUnsafePointer () #94 0x00000001d4b6fe08 in mutateEngine () #95 0x00000001d49318d4 in generic specialization of SwiftUI.UnaryChildGeometry.worth.getter : SwiftUI.ViewGeometry () #96 0x00000001d49413a4 in merged generic specialization > of implicit closure #1 (Swift.UnsafeMutableRawPointer, __C.AGAttribute) -> () in closure #1 () -> (Swift.UnsafeMutableRawPointer, __C.AGAttribute) -> () in closure #1 (Swift.UnsafePointer) -> AttributeGraph.Attribute in AttributeGraph.Attribute.init(τ_1_0) -> AttributeGraph.Attribute () #97 0x00000001c00ca438 in AG::Graph::UpdateStack::replace () #98 0x00000001c00cac04 in AG::Graph::update_attribute () #99 0x00000001c00d80b4 in AG::Subgraph::replace () #100 0x00000001d4d6f118 in SwiftUI.ViewGraph.updateOutputs(async: Swift.Bool) -> () () #101 0x00000001d4d6f618 in closure #2 () -> () in SwiftUI.ViewGraph.updateOutputsAsync(at: SwiftUI.Time) -> Swift.Optionally available () #102 0x00000001c00e70f8 in AGGraphWithMainThreadHandler () #103 0x00000001d4d69a90 in updateOutputsAsync () #104 0x00000001d4d643c4 in renderAsync () #105 0x00000001d3b436d4 in displayLinkTimer () #106 0x00000001d3b43eb4 in SwiftUI.DisplayLink.displayLinkTimer(__C.CADisplayLink) -> () () #107 0x00000001d3b444c0 in @objc SwiftUI.DisplayLink.displayLinkTimer(__C.CADisplayLink) -> () () #108 0x000000018b3e2e44 in CA::Show::DisplayLinkItem::dispatch_ () #109 0x000000018b3def44 in CA::Show::DisplayLink::dispatch_items () #110 0x000000018b4e7a40 in display_timer_callback () #111 0x00000001803ed914 in __CFMachPortPerform () #112 0x0000000180429a6c in __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ () #113 0x0000000180429084 in __CFRunLoopDoSource1 () #114 0x000000018042397c in __CFRunLoopRun () #115 0x0000000180422cec in CFRunLoopRunSpecific () #116 0x0000000180f0e38c in -[NSRunLoop(NSRunLoop) runMode:beforeDate:] () #117 0x0000000180f0e55c in -[NSRunLoop(NSRunLoop) run] () #118 0x00000001d3b45830 in perform signature specialization of static SwiftUI.DisplayLink.asyncThread(arg: Swift.Optionally available) -> () () #119 0x00000001d3b44520 in @objc static SwiftUI.DisplayLink.asyncThread(arg: Swift.Optionally available) -> () () #120 0x0000000180f35148 in __NSThread__start__ () #121 0x0000000102cee5f0 in _pthread_start ()
The warning that’s seen when operating on the iPhone 15 simulator with iOS 17.5 is as follows:
warning: information race detected: @MainActor perform at StackOverflow/ContentView.swift:52 was not referred to as on the principle thread
Line 52 is the ForEach contained in the perform itemList.
It appears to me that this have to be a SwiftUI bug, particularly since it is just underneath sure circumstances. For instance, the problem will not be seen when any of the next modifications are made:
- a distinct textual content dimension is used
- the second textual content merchandise is shorter (1 line as a substitute of three)
- any 1 of the three views inside
ViewthatFitsis commented out - vertical padding is added to the chevron
- the chevron is faraway from view.
These modifications should not fixing the issue, they’re simply stopping it from occurring for the setup described. So I would like a extra dependable repair. Specifically, I’m questioning if there could be a method to stop the issue with some sort of annotation or actor directive within the code?
How can the code be fastened in order that the problems should not seen when operating as described?