Xcode Previews

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Create an app UI and configure almost everything your users see using Xcode Previews.

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How to await inside SwiftUI a #Preview?
In order to setup a preview, I need to create a Book; to do that, I need to await a function – however, one cannot await inside a Preview: import SwiftUI struct BookView: View { let book: Book var body: some View { VStack { Image(book.thumbnail, scale: 1.0, label: Text(book.title)) } } } #Preview { let url = URL(filePath: "/Users/dan/Documents/Curs confirmare RO.pdf")! // 👇 here, `createBook` should be awaited; but how? let book = createBook(for: url, of: CGSize(width: 254, height: 254), scale: 1.0) BookView(book: book) }
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466
Mar ’25
Using @Namespace in #Preview Xcode 15 gives an error message
Greetings... I am trying to use @Namespace for my matchedGeometryEffect use case. prior to Xcode 15 beta the following code worked just fine: struct ChapterItem_Previews: PreviewProvider { @Namespace static var namespace static var previews: some View { ChapterItem(namespace: namespace, show: .constant(true)) } } However trying to do the same within the new Xcode 15 beta #Preview Macro #Preview { @Namespace var namespace ChapterItem(namespace: namespace, show: .constant(true)) } produces the following error message: Ambiguous use of 'Preview(_:traits:body:)' May I kindly get assistance on the proper way I can get this to work in Xcode 15 beta? Please be as detail as you can since I'm still new to swiftUI as well Thank You.
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2.3k
Mar ’25
Question about using @Previewable
This is an issue that occurred while using SwiftUI. Cannot find '$state' in scope The other view finds properties normally. May I know why the error is occurring? The following code is the full text of the code that causes problems. import SwiftUI @Observable class HomeState { var title: String = "Home" } struct HomeView: View { @Binding var state: HomeState var body: some View { Text(state.title) } } #Preview { @Previewable @State var state: HomeState = .init() HomeView(state: $state) /// Error: Cannot find '$state' in scope } The same error occurs when using the String type rather than the object. What did I do wrong?
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239
Mar ’25
Previews due to SwiftData Predicates in Xcode 16.3
My preview crashes whenever I compare my model's value to a constant's stored value. I use struct constants with a stored value as alternatives to enums, (IIRC ever since the beginning) enums never worked at all with .rawValue or computed properties. This crashes when it runs on Xcode 16.3 beta and iOS 18.4 in previews. It doesn't appear to crash in simulator. @Model class Media { @Attribute(.unique) var id: UUID = UUID() @Attribute var type: MediaType init(type: MediaType) { self.type = type } static var predicate: (Predicate<Media>) { let image = MediaType.image.value let predicate = #Predicate<Media> { media in media.type.value == image } return predicate } } struct MediaType: Codable, Equatable, Hashable { static let image: MediaType = .init(value: 0) static let video: MediaType = .init(value: 1) static let audio: MediaType = .init(value: 2) var value: Int } My application crashes with "Application crashed due to fatalError in Schema.swift at line 320." KeyPath \Media.<computed 0x000000034082a33c (MediaType)>.value points to a field (<computed 0x000000034082a33c (MediaType)>) that is unknown to Media and cannot be used. This appears to also occur if I am using a generic/any func and use protocols to access a property which is a simple String, such as id or name, despite it being a stored SwiftData attribute. I filed a bug report, but looking to hear workarounds.
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643
Mar ’25
Crash When Previewing w/ Struct Binding Reassignment In Constructor
Platform Specs: Xcode 16.2 Swift 6.0.3 iOS 18.2 + iOS Simulator 18.3.1 Issue: Refer to the following code: struct CustomView: View { @Binding var prop: CustomStruct init(prop p: Binding<CustomStruct>) { _prop = p } init(isPreview: Bool) { let p = CustomStruct() _prop = .constant(p) } var body: some View { VStack { Text("hi") } } } #Preview { CustomView(isPreview: true) .preferredColorScheme(.dark) } The first constructor is for normal app functionality (and previews/functions correctly when used with the rest of the app in the ContentView preview tab). The second constructor is for previewing only CustomView in its own preview tab. This constructor does not work when previewing in the same file, as shown above. It triggers an ambiguous crash, stating that the diagnostic log (which obviously provides no clear information) should be checked. I have isolated the issue to be in the Binding reassignment in the second constructor. Replacing CustomStruct with anything but another struct, like an enum or primitive, fixes the issue. Note: This bug only occurs when previewing (either through the #Preview macro or PreviewProvider struct).
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290
Mar ’25
Simple console display test - preview not working as expected
Just learning Swift and SwiftUI, having fun in Xcode. I have the following custom view defined, but when I try to test it, the information doesn't get updated as I expect. When I use the button defined INSIDE the custom view, the update works as expected. When I use the button defined in the Preview body, it doesn't. The "lines" variable of the custom view appears not to be updated in that case. I know I'm missing something fundamental here about either view state binding or the preview environment, but I'm stumped. Any ideas? import SwiftUI struct ConsoleView: View { var maxLines : Int = 26 private enum someIDs { case textID} @State private var numLines : Int = 0 @State var lines = "a\nb\nc\n" var body: some View { VStack(alignment: .leading, spacing:0 ) { ScrollViewReader { proxy in ScrollView { Button("Scroll to Bottom") { withAnimation { proxy.scrollTo(someIDs.textID, anchor: .bottom) } } Text(lines) .id(someIDs.textID) .multilineTextAlignment(.leading) .frame(maxWidth: .infinity, alignment: .bottomLeading) .padding() .onChange ( of: lines) { withAnimation { proxy.scrollTo( someIDs.textID, anchor: .bottom) } } } Button("Add more") { writeln("More") //writeln(response) } } } } private func clipIfNeeded () { if (numLines>=maxLines) { if let i = lines.firstIndex(of: "\n") { lines = String(lines.suffix( from: lines.index(after:i))) } } } func writeln ( _ newText : String) { print("adding '\(newText)' to lines") //clipIfNeeded() write( newText ) write("\n") numLines += 1 print(lines) } func write ( _ newText : String) { lines += newText } } #Preview { VStack() { var myConsole = ConsoleView(lines: "x\ny\nz\n") myConsole Button("Add stuff") { myConsole.writeln("Stuff") } } }
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360
Feb ’25
Gathering Required Information for Troubleshooting Xcode Previews or Swift Previews Issues
Hi, You're here because your project has issues related to Xcode Previews or Swift Previews. The issue you're experiencing may be the result of any of the following: An error in your SwiftUI app, Xcode previews, or on-device previews. A configuration error in your Xcode project, including any third-party dependencies or packages. A system issue in the operating system, SwiftUI, or in Xcode Previews. Based on your request, I need more information about your SwiftUI app when rendering Xcode Previews or on-device previews. Specifically, I’ll need the diagnostics Swift Previews generates to make sure I understand the error encountered by the preview system. Please create a report in Feedback Assistant to share the details requested in the instructions below. For issues with macOS, Mac Catalyst, on-device iOS, or on-device visionOS previews, perform the following steps to gather diagnostics: Download and install the Swift Previews logging profile for your device. Reproduce the error while previewing on device, taking note of the timestamp when the error occurred. Attach the Previews diagnostics, sysdiagnose from your Mac, a sysdiagnose from the previewing iOS or visionOS device. For issues with Xcode Previews, perform the following steps to gather diagnostics: Download and install the Swift Previews logging profile for your device. Reproduce the error in Xcode Previews, if you haven’t already done so. If an error banner appears in the canvas, click the "Diagnostics" button within the banner, then go to Step 5; otherwise, continue to Step 4. If the error banner is missing, navigate to the menu in Xcode: Editor > Canvas > Diagnostics In the presented sheet, click the "Generate Report" button. Attach a zip file containing the diagnostic report to your bug report (it will be named something like previews-diagnostics-0123456789.zip). Submitting your feedback Before you submit to Feedback Assistant, please confirm the following information is included in your feedback: with the Swift Previews logging profile installed, attach the sysdiagnose logs gathered after reproducing the issue the Previews diagnostics generated by Xcode timestamp identifying when the issue was reproduced focused sample Xcode project that reproduces the issue (if applicable) screenshots or videos of the error (optional) Please include all requested information to prevent delays in my investigation. After your submission to Feedback Assistant is complete, please respond to your original Forums post with the Feedback ID. Once received, I can begin my investigation and determine if this issue is caused by an error within your SwiftUI app, a configuration issue within your Xcode project, or an underlying issue in the operating system, SwiftUI, in Xcode Previews, or on-device previews. Cheers, Paris X Pinkney |  WWDR | DTS Engineer
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393
Feb ’25
Xcode 16 no longer sets ENABLE_PREVIEWS=YES for preview builds
Up until now, it was possible to check in build scripts via the ENABLE_PREVIEWS environment variable whether a build for a SwiftUI preview is being executed. In addition, it was also possible to conditionally compile code for SwiftUI or exclude it from compilation using this variable. This no longer works with Xcode 16 and the new SwiftUI Preview compilation! There is still the option to switch to the old system with the "Use Legacy Previews Execution" setting, but as stated in the release notes, this option will be removed at some point. Which brings us back to the old problem of not being able to exclude build scripts from preview builds and not being able to prevent certain code from being compiled / add special code for SwiftUI previews. This is a terrible situation, especially for more complex projects in which precisely the points mentioned are important for the build process. I seriously hope Apple provides us with another environment variable for SwiftUI preview builds that we can use.
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6.3k
Feb ’25
Xcode Preview Crashes: "xcpreviewagent crashed because Alamofire.framework is missing"
Question: I have created a workspace containing a SwiftUI app and two frameworks: B Framework: Handles UI components C Framework: Handles service classes I added a Podfile to manage dependencies. My Podfile is structured as follows: inhibit_all_warnings! workspace 'ABC.xcworkspace' def shared_pods # Shared pods here pod 'Alamofire' end target 'A' do use_frameworks! project 'A/A.xcodeproj' shared_pods end target 'B' do use_frameworks! project 'B/B.xcodeproj' shared_pods end target 'C' do use_frameworks! project 'C/C.xcodeproj' shared_pods end post_install do |installer| installer.pods_project.targets.each do |target| target.build_configurations.each do |config| config.build_settings['IPHONEOS_DEPLOYMENT_TARGET'] = '13.0' end end end After installing pods and building the project, everything works fine except for Xcode’s SwiftUI Preview, which crashes with the following error: xcpreviewagent crashed because Alamofire.framework is missing Question: How can I resolve this issue and make SwiftUI Previews work without Xcode crashing?
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409
Feb ’25
Cannot preview in this file, failed to launch
I am not able to use SwiftUI Preview Here is the report I get while trying to see the issue: Here is the report of the issue: And here is the call and code preview: import SwiftUI struct ContentView: View { var body: some View { VStack { Image(systemName: "globe") .imageScale(.large) .foregroundStyle(.tint) Text("Hello, world!") } .padding() } } #Preview { ContentView() } Please update.
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784
Jan ’25
Preview won't load on Mac-OS/Multiplatform Swift-App
Hey, I wanted to create a Mac-OS application. Normally I only code iPhone apps. But as soon as I want to display anything on the preview, it loads, just as normal, and then the throbber/progress indicator disappears and the preview canvas stays gray like it used to be before. I also don't get any error messages. Only one time after trying different things I got one message saying: "Could not launch Preview Shell." and "Could not create FBSOpenApplicationService." I also searched for a few solutions and tried some but none of them seemed to work. In the DiagnosticReports were some files of the time but I didn't seem to find anything helpful in there and they don't appear when I reopen my project or switch from PreviewMode "My Mac" to "iPhone 16 Pro". When I launch the app on a simulator it works perfectly fine but this is quite annoying. Thanks for trying to help me!
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358
Jan ’25
Unable to display SwiftUI View Previews in a Static Framework target
Hello, I am currently encountering an issue where SwiftUI View Previews cannot be displayed when the View is defined in a Static Framework target. This issue only occurs under specific conditions. Environment Xcode: 16.2 Scheme Structure: MainApp Test Target: TestHogeFeature Test Setting: Gather coverage (Code coverage collection) enabled(all) Target Structure: MainApp (Application target) Dependencies: [HogeFeature, Core] HogeFeature (Static Framework target) Dependencies: [Core] Core (Framework target) Dependencies: None TestHogeFeature (Unit test target) Dependencies: [HogeFeature] Summary I am currently working on a SwiftUI-based project and have encountered an issue where Previews fail to display under specific conditions. Below are the details: Issue In the MainApp scheme, when the code coverage collection setting (Gather coverage for) is enabled, Previews for SwiftUI Views within the HogeFeature (Static Framework) target fail to display correctly. However, the issue is resolved by taking one of the following actions: Change HogeFeature from a Static Framework to a Dynamic Framework. Remove the build setting MACH_O_TYPE: staticlib Disable the Gather coverage setting in the MainApp scheme. I have attached the actual error log from the failed Preview. preview error log Questions Why does this issue occur only when using a Static Framework with code coverage enabled? Is there any way to resolve this issue while maintaining the current configuration (Static Framework with code coverage enabled)? I would appreciate any advice or insights regarding the cause and potential solutions.
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468
Jan ’25
Why are asynchronous tasks not executed in Xcode Canvas, and why do they only work in the simulator?
Hi everyone, I'm new to Xcode and iOS development. I've encountered an issue where asynchronous tasks seem to not execute in Xcode Canvas, but they work fine in the simulator. Can anyone explain why this might be happening or what I could do to fix it? Thank you for your help! struct PartnerProfileView: View { @State private var showSheet: Bool = true let partnerName: String var body: some View { ZStack(alignment: .bottom) { Color("EFEFF4_0F2534") ScrollView(showsIndicators: false) { headerSection() infoSection() .padding(.bottom, 5) sectionTitle("Other Skills") skillsGrid() sectionTitle("···") dynamicsSection() } .frame(maxWidth: .infinity, maxHeight: .infinity) CustomTabBar() } .navigationBarHidden(true) .ignoresSafeArea(edges: .all) .onAppear { print("PartnerProfileView received") Task { await BottomCustomPopup().present() } } .onChange(of: showSheet) { oldState, newValue in print("oldState \(oldState)") print("newValue \(newValue)") } } } //@MainActor struct BottomCustomPopup: BottomPopup { var body: some View { HStack(spacing: 0) { Text("Hello World") Spacer() Button(action: { Task { await dismissLastPopup() }}) { Text("Dismiss") } } .padding(.vertical, 20) .padding(.leading, 24) .padding(.trailing, 16) } }
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355
Jan ’25
Preview and bundle for modular app target
I have a dummy project that is set up in the following way: one Xcode project two frameworks, UI and Feature, Feature embeds UI-framework three app targets, two that are SwiftUI lifecycle and one UIKit lifecycle all app targets import the Feature framework all app targets have same setup for asset catalogue The point of this setup is to be able to switch between app target scheme and see preview changes accordingly. That works 100% with anything coming from the asset catalogue and even localization catalogues. The dummy project exists as a proof of concept for the main project (8 years old, all Swift) I am working on. However, the same setup does not work in the main project. I am suspecting it has to do with how the project is initialised and bundles. I print out the bundles to see which bundles are registered. Dummy project will print out the bundle based on app target, the main bundle being based on the selected scheme. The main project will have the previews.com.apple.PreviewAgent.iOS as main bundle.
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397
Jan ’25
Xcode 15 preview loads indefinitely
I've recently started learning how to make IOS apps, but when trying to load the preview, it just shows the loading animation indefinitely. I am running xcode 15.2 (because my mac is a bit old and doesn't run the latest version) I have tried using version 15.1 but it still doesn't work, only works when I go down to version 14.3.1, but that changes the swift code.
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Dec ’24