I've encountered the same issue and was able to track down the root cause.
The problem occurs if:
The project uses a library
The library contains an Objective C extension on a UIKit class with a load method that calls some other method
It doesn't seem to matter which method is called in load, anything seems to break previews.
I've shared an minimal example of the issue here:
https://www.icloud.com/iclouddrive/024UlszLOLDUPKFsKSllSK72g#FailedToLaunchApp
Steps to reproduce:
Open the PreviewLaunchExample.xcodeproj and try to show the Preview of the ContentView on any iOS 18 device. It will timeout with the error "Failed to launch app "PreviewLaunchExample.app" in reasonable time". The Preview does work when selecting a iOS 17.5 device, as others have reported in this thread.
Next, open Test.m in MyLibrary and comment out the line [self description]. Then test the Preview again. The Preview should work as expected.
Test setup: macOS 15.0, Xcode 16.0, OS 18 Simulator.
jasamer
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I have found a solution. The idea is to read the size of the scroll view and use it as the minimum size of the view inside.
extension View {
func readSize(onChange: @escaping (CGSize) -> Void) -> some View {
background(
GeometryReader { geometryProxy in
Color.clear
.preference(key: SizePreferenceKey.self, value: geometryProxy.size)
}
)
.onPreferenceChange(SizePreferenceKey.self, perform: onChange)
}
}
struct ExampleView: View {
@State var size: CGSize = .zero
var body: some View {
ScrollView([.horizontal, .vertical]) {
Text("Hello World!")
.frame(minWidth: size.width, minHeight: size.height, alignment: .topLeading)
}
.readSize(onChange: { size = $0 })
}
}
Somewhat ugly, but it works.