Explore the various UI frameworks available for building app interfaces. Discuss the use cases for different frameworks, share best practices, and get help with specific framework-related questions.

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LazyHstack in SwiftUI not supporting varying height views
In SwiftUI I want to create a list with LazyVstack and each row item in the LazyVstack is a LazyHstack of horizontally scrollable list of images with some description with line limit of 3 and width of every item is fixed to 100 but height of every item is variable as per description text content. But in any of the rows if the first item has image description of 1 line and the remaining items in the same row has image description of 3 lines then the LazyHStack is truncating all the image descriptions in the same row to one line making all the items in that row of same height. Why LazyHStack is not supporting items of varying height ? Expected behaviour should be that height of every LazyHStack should automatically adjust as per item content height. But it seems SwiftUI is not supporting LazyHstack with items of varying height. Will SwiftUI ever support this feature?
Topic: UI Frameworks SubTopic: SwiftUI
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260
Feb ’25
high internal cpu usage
Hi, I am developing a new SwiftUI app. Running under OSX, I see very high cpu usage (I am generating lots of gpu based updates which shouldn't affect the cpu). I have used the profiler to ensure my swift property updates are minimal, yet the cpu usage is high coming from SwiftUI. It seems the high cpu usage is coming from NSAppearance, specifically, CUICopyMeasurements - for a single button??? But the swift updates don't show any buttons being updating
Topic: UI Frameworks SubTopic: SwiftUI
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270
Feb ’25
Magnification Gesture conflicts with UIPageViewController scroll gesture
The Problem I am trying to implement a pinch-to-zoom feature on images within a UIPageViewController. However, often times when trying to pinch to zoom, the magnification gesture gets overridden by the scrolling gesture built into the UIPageViewController. I'm not sure how to get around this. The Apple Photos app seems to allow pinch to zoom on photos inside a full-page scrolling view without any issue, so I believe it should be possible. Versions: iOS 17.2.1 - iOS 18.2.1, Swift (SwiftUI), Xcode 15.1 Steps to Reproduce Run this sample Xcode project on a physical device: https://drive.google.com/file/d/1tB1QyY6QPEp-WLzdHxgDdkM45xCAELLr/view?usp=share_link Try pinching to zoom on the image. After a few goes at it, you'll likely find that one time it will scroll instead of pinching to zoom. It might take up to a dozen pinches to experience this issue. What I've Tried Making the magnification gesture a high priority gesture. Having only one page in the paging view controller. Subclassing UIScrollView and conforming to the UIGestureRecognizerDelegate in that subclass, as explained here: https://stackoverflow.com/a/51070947/12218938 Using the iOS 17 ScrollView instead. Unfortunately it has the same issue but even worse! It's possible that since this is a native SwiftUI view, people might have solutions to this, but from a brief search I couldn't find any. If you set the data source to nil (which indicates that there are no other pages for the paging view controller to scroll to), it does work, but it's not a workable solution since the time you'd want to set the data source to nil is when the user pinches the screen, but you can't know when the user pinches the screen if the gesture doesn't work! Other Ideas/Workarounds We could have some "zoom" mode that temporarily cancels the ability to scroll while zooming. But this seems like not too nice/intuitive of a solution. If there is no paging view that Apple provides which could be made compatible with a pinch-to-zoom gesture, it's possible we would have to make a completely custom paging view. But that would be a lot of work I presume, so it's probably not something we would have time for right now.
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Jan ’25
Detect change to apps Screen Time Access
I'm creating an app which gamifies Screen Time reduction. I'm running into an issue with apples Screen Time setting where the user can disable my apps "Screen Time access" and get around losing the game. Is there a way to detect when this setting is disabled for my app? I've tried using AuthorizationCenter.shared.authorizationStatus but this didn't do the trick. Does anyone have an ideas?
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Feb ’25
UIDocumentPickerViewController
I'm upgrading my app from minVersion iOS 11 to iOS 12. My compiler says that UIDocumentMenuViewController with UIDocumentPickerViewController is deprecated, they recommend to use directly the last one. So I change the code. fileprivate func openDocumentPicker() { let documentPicker = UIDocumentPickerViewController( documentTypes: [ "com.adobe.pdf", "org.openxmlformats.wordprocessingml.document", // DOCX "com.microsoft.word.doc" // DOC ], in: .import ) documentPicker.delegate = self view.window?.rootViewController?.present(documentPicker, animated: true, completion: nil) } When I open the picker in iOS 17.2 simulator and under it is well shown, like a page sheet. But in iOS 18.0 and up at first it opens like a page sheet with no content but then it is displayed as a transparent window with no content. Is there any issue with this component and iOS 18? If I open the picker through UIDocumentMenuViewControllerDelegate in an iphone with iOS 18.2 it is well shown. Image in iOS 18.2 with the snippet The same snippet in iOS 17.2 (and expected in older ones)
Topic: UI Frameworks SubTopic: UIKit Tags:
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350
Jan ’25
XCode breakpoint possible for "Publishing changes from within view updates is not allowed, this will cause undefined behavior."?
Dear Sirs, I'm searching for the most straightforward way to identify the root of a "Publishing changes from within view updates is not allowed, this will cause undefined behavior." warning. It is a complex SwiftUI project and I think there should be a better way than just try and error with disabling/removing and enabling/adding different screen elements to check if the warning still is shown. I tried to set a symbolic breakpoint for "os_log" in my XCode project and indeed this is triggered right before the warning appears but the callstack doesn't give me a direct hint to the part of my code which causes this warning. What would be the most direct way and is there something like an exception handler in such cases? Thanks and best regards, Johannes
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Jan ’25
SwiftUI glitch with coloreffect shader & orientation change
Hi, I have the following swiftUI code: Image(uiImage: image) .resizable() .aspectRatio(contentMode: .fit) .colorEffect(ShaderLibrary.AlphaConvert()) and the following shader: [[ stitchable ]] half4 AlphaConvert(float2 position, half4 currentColor) { return half4(currentColor.r>0.5,currentColor.r<=0.5,0,(currentColor.r>0.5)); } I am loading a full-res image from my photo library (24MP)... The image initially displays fine, with portions of the image red, and the rest black (due to alpha blending)... However, after rotating the device, I get an image that is a combination of red&green... Note, that the green pixels from the shader have alpha 0, hence, should never be seen. Is there something special that needs to be done on orientation changes so that the shader works fine?
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Dec ’24
Using AsyncStream vs @Observable macro in SwiftUI (AVCam Sample Code)
I want to understand the utility of using AsyncStream when iOS 17 introduced @Observable macro where we can directly observe changes in the value of any variable in the model(& observation tracking can happen even outside SwiftUI view). So if I am observing a continuous stream of values, such as download progress of a file using AsyncStream in a SwiftUI view, the same can be observed in the same SwiftUI view using onChange(of:initial) of download progress (stored as a property in model object). I am looking for benefits, drawbacks, & limitations of both approaches. Specifically, my question is with regards to AVCam sample code by Apple where they observe few states as follows. This is done in CameraModel class which is attached to SwiftUI view. // MARK: - Internal state observations // Set up camera's state observations. private func observeState() { Task { // Await new thumbnails that the media library generates when saving a file. for await thumbnail in mediaLibrary.thumbnails.compactMap({ $0 }) { self.thumbnail = thumbnail } } Task { // Await new capture activity values from the capture service. for await activity in await captureService.$captureActivity.values { if activity.willCapture { // Flash the screen to indicate capture is starting. flashScreen() } else { // Forward the activity to the UI. captureActivity = activity } } } Task { // Await updates to the capabilities that the capture service advertises. for await capabilities in await captureService.$captureCapabilities.values { isHDRVideoSupported = capabilities.isHDRSupported cameraState.isVideoHDRSupported = capabilities.isHDRSupported } } Task { // Await updates to a person's interaction with the Camera Control HUD. for await isShowingFullscreenControls in await captureService.$isShowingFullscreenControls.values { withAnimation { // Prefer showing a minimized UI when capture controls enter a fullscreen appearance. prefersMinimizedUI = isShowingFullscreenControls } } } } If we see the structure CaptureCapabilities, it is a small structure with two Bool members. These changes could have been directly observed by a SwiftUI view. I wonder if there is a specific advantage or reason to use AsyncStream here & continuously iterate over changes in a for loop. /// A structure that represents the capture capabilities of `CaptureService` in /// its current configuration. struct CaptureCapabilities { let isLivePhotoCaptureSupported: Bool let isHDRSupported: Bool init(isLivePhotoCaptureSupported: Bool = false, isHDRSupported: Bool = false) { self.isLivePhotoCaptureSupported = isLivePhotoCaptureSupported self.isHDRSupported = isHDRSupported } static let unknown = CaptureCapabilities() }
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376
Dec ’24
NSDocumentController subclass with remembered document options
Hi all, I am trying to allow users of my app to select extra options when opening documents, and to remember those options when re-opening documents at launch. So far best idea I have is: Subclass NSDocumentController to provide an NSOpenPanel.accessoryView with the options Create a URL bookmark for each opened file and keep a mapping of bookmarks to options On launch and when the recent documents list changes, prune the stored mappings to match only the recent items Has anyone done this before, or know of a better approach? Thank you.
Topic: UI Frameworks SubTopic: AppKit
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280
Feb ’25
NSTextField Delegates Not Triggering After Refactoring NSView to NSViewController in macOS App
I'm developing a macOS application and facing an issue with NSTextField delegates after refactoring my code. Here's the situation: I have an NSWindowController. Inside the NSWindowController, there's a container NSView named containerView. On top of containerView, I added a custom NSView subclass named MyDetailsView. MyDetailsView has two NSTextField instances, and their delegates are properly set. The delegate methods like controlTextDidChange(_:) were getting called as expected. Due to some additional requirements, I refactored MyDetailsView into MyDetailsViewController, a subclass of NSViewController. I created a corresponding .xib file for MyDetailsViewController. Updated the code to load and add MyDetailsViewController's view (view property) to containerView. Verified that the NSTextField delegates are still being set, and the fields are displayed correctly in the UI. However, after this refactor, the NSTextField delegate methods (e.g., controlTextDidChange(_:)) are no longer being triggered. **What I've Tried: ** Verified that the delegates for the NSTextField instances are correctly set after the refactor. Ensured that the MyDetailsViewController's view is added to containerView. Question: What could be causing the NSTextField delegate methods to stop working after refactoring from NSView to NSViewController? @IBOutlet weak var customeView: NSView! var myDetailsViewController: MyDetailsViewController! var myDetailsView: MyDetailsView! var isViewController: Bool = true override func windowDidLoad() { super.windowDidLoad() if isViewController { myDetailsViewController = MyDetailsViewController(nibName: "MyDetailsViewController", bundle: nil) self.customeView.addSubview(myDetailsViewController.view) } else { myDetailsView = MyDetailsView.createFromNib() self.customeView.addSubview(myDetailsView!) } } override func showWindow(_ sender: Any?) { super.showWindow(nil) window?.makeKeyAndOrderFront(nil) } override var windowNibName: NSNib.Name? { return NSNib.Name("MyWindowController") }} class MyDetailsViewController: NSViewController { @IBOutlet weak var textField: NSTextField! override func viewDidLoad() { super.viewDidLoad() // Do view setup here. } } extension MyDetailsViewController: NSTextDelegate { func controlTextDidChange(_ obj: Notification) { guard let textField = obj.object as? NSTextField else { return } print("The value is ----> (MyDetailsViewController) \(textField.stringValue)") } } TextField delegate is set in XIB.
Topic: UI Frameworks SubTopic: AppKit Tags:
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394
Dec ’24
Page Freeze Caused by Gesture
When pushing a page in the navigation, changing the state of interactivePopGestureRecognizer causes the page to freeze. Just like this: #import "ViewController.h" @interface ViewController () @end @implementation ViewController - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. CGFloat red = (arc4random_uniform(256) / 255.0); CGFloat green = (arc4random_uniform(256) / 255.0); CGFloat blue = (arc4random_uniform(256) / 255.0); CGFloat alpha = 1.0; // self.view.backgroundColor = [UIColor colorWithRed:red green:green blue:blue alpha:alpha]; UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom]; btn.frame = CGRectMake(0, 0, 100, 44); btn.backgroundColor = [UIColor redColor]; btn.center = self.view.center; [btn setTitle:@"push click" forState:UIControlStateNormal]; [btn addTarget:self action:@selector(click:) forControlEvents:UIControlEventTouchUpInside]; [self.view addSubview:btn]; } - (void)click:(id)sender { [self.navigationController pushViewController:[ViewController new] animated:YES]; } - (void)viewWillAppear:(BOOL)animated{ [super viewWillAppear:animated]; self.navigationController.interactivePopGestureRecognizer.enabled = NO; } - (void)viewDidAppear:(BOOL)animated{ [super viewDidAppear:animated]; self.navigationController.interactivePopGestureRecognizer.enabled = YES; } @end
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328
Feb ’25
How to return a UIMenu for read-only UITextView
I have a UITextView being added at runtime to a UIImageView as the result of doing text recognition. It's set to be editable = NO and selectable = YES. When I set the text and select it, it asks the delegate for the menu to display via: textView:editMenuForTextInRange:suggestedActions: The suggested items contains many UIAction and UICommand objects that have private methods or do not have the destructive attribute set, yet they are destructive. Some of these are: promptForReplace: transliterateChinese: _insertDrawing: _showTextFormattingOptions: I need to return a menu that has only non-destructive commands in it. First, why isn't UITextView sending only non-destructive suggested commands when its editable is NO? Second, how can I filter the array of suggested commands when it's impossible to know if they're destructive (as some are missing that attribute)? In addition to that, even non-destructive commands are causing an unrecognized selector exception, such as the Speak command, which it is sending to my view controller instead of to the UITextView, which is the only thing that knows what the text is that it should speak.
Topic: UI Frameworks SubTopic: UIKit
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176
Feb ’25
SwiftUI infinite rendering loop when using a custom Binding to a dictionary-based store
I’m building a SwiftUI app where the struct AppGroup is identified by a UUID and stored in a dictionary. My Task model has appGroupId: UUID?. In TaskDetailView, I create a custom Binding<AppGroup> from the store, then navigate to AppGroupDetailView. However, when I tap the NavigationLink, the console spams logs, CPU hits 100%, and it never stabilizes. Relevant Code AppGroupStore (simplified) class AppGroupStore: ObservableObject { @Published var appGroupsDict: [UUID: AppGroup] = [:] func updateAppGroup(_ id: UUID, appGroup: AppGroup) { appGroupsDict[id] = appGroup } // Returns a binding so views can directly read/write the AppGroup by id func getBinding(withId id: UUID?) -> Binding<AppGroup> { Binding( get: { if let id = id { return self.appGroupsDict[id] ?? .empty } return .empty }, set: { newValue in print("New value set for \(newValue.name)") self.updateAppGroup(newValue.id, appGroup: newValue) } ) } // ... } AppGroup is a simple struct: struct AppGroup: Identifiable, Codable { let id: UUID var name: String var apps: [String] static let empty = AppGroup(id: UUID(), name: "Empty", apps: []) } TaskDetailView (main part) struct TaskDetailView: View { @Binding var task: ToDoTask // has task.appGroupId: UUID? @EnvironmentObject var appGroupStore: AppGroupStore var body: some View { let appGroup = appGroupStore.getBinding(withId: task.appGroupId) print("Task load") // prints infinitely, CPU 100% return List { // ... NavigationLink(destination: AppGroupDetailView(appGroup: appGroup)) { Text(appGroup.wrappedValue.name) } } .navigationTitle(task.name) } } AppGroupDetailView (simplified) struct AppGroupDetailView: View { @Binding var appGroup: AppGroup // ... var body: some View { List { ForEach(appGroup.apps, id: \.self) { app in Text(app) } } .navigationTitle(appGroup.name) } } Symptoms: Tapping the NavigationLink leads to infinite “Task load” logs and 100% CPU usage. The set closure (“New value set for...”) is never called, so it’s not repeatedly writing. If I replace the Binding<AppGroup> with a read-only approach (just accessing the dictionary), it does not get stuck. Question: What might cause SwiftUI to keep re-rendering the body indefinitely, even if my custom get closure doesn’t explicitly mutate the state? Are there known pitfalls when using a dictionary-based store and returning a Binding like this? Any help is much appreciated! Thanks in advance for your insights!
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239
Jan ’25
How do I make a UIViewRepresentable beneath SwiftUI elements ignore touches to these elements?
Hello, and an early "Merry Christmas" to all, I'm building a SwiftUI app, and one of my Views is a fullscreen UIViewRepresentable (SpriteView) beneath a SwiftUI interface. Whenever the user interacts with any SwiftUI element, the UIView registers a hit in touchesBegan(). For example, my UIView has logic for pinching (not implemented via UIGestureRecognizer), so whenever the user holds down a SwiftUI element while touching the UIView, that counts as two touches to the UIView which invokes the pinching logic. Things I've tried to block SwiftUI from passing the gesture down to the UIView: Adding opaque elements beneath control elements Adding gestures to the elements above Adding gesture masks to the gestures above Converting eligible elements to Buttons (since those seem immune) Adding SpriteViews beneath those elements to absorb gestures So far nothing has worked. As long as the UIView is beneath SwiftUI elements, any interactions with those elements will be registered as a hit. The obvious solution is to track each SwiftUI element's size and coordinates with respect to the UIView's coordinate space, then use exclusion areas, but this is both a pain and expensive, and I find it hard to believe this is the best fix for such a seemingly basic problem. I'm probably overlooking something basic, so any suggestions will be greatly appreciated
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434
Dec ’24
Publishing changes from within view updates is not allowed - SwiftUI with ARKit
Hello, I’m encountering the error "Publishing changes from within view updates is not allowed, this will cause undefined behavior". while developing an app using SwiftUI and ARKit. I have a ObjectTracking class where I update some @Published variables inside a function called processObjectAttributes after detecting objects. However, when I try to update these state variables in the View (like isPositionChecked, etc.), the error keeps appearing. Here is a simplified version of my code: class ObjectTracking: ObservableObject { @Published var isPositionChecked: Bool = false @Published var isSizeChecked: Bool = false @Published var isOrientationChecked: Bool = false func checkAttributes(objectAnchor: ARObjectAnchor, _ left: ARObjectAnchor.AttributeLocation, _ right: ARObjectAnchor.AttributeLocation? = nil, threshold: Float) -> Bool { let attributes = objectAnchor.attributes guard let leftValue = attributes[left]?.floatValue else { return false } let rightValue = right != nil ? attributes[right!]?.floatValue ?? 0 : 0 return leftValue > threshold && (right == nil || rightValue > threshold) } func isComplete(objectAnchor: ARObjectAnchor) -> Bool { isPositionChecked = checkAttributes(objectAnchor: objectAnchor, .positionLeft, .positionRight, threshold: 0.5) isSizeChecked = checkAttributes(objectAnchor: objectAnchor, .sizeLeft, .sizeRight, threshold: 0.3) isOrientationChecked = checkAttributes(objectAnchor: objectAnchor, .orientationLeft, .orientationRight, threshold: 0.3) return isPositionChecked && isSizeChecked && isOrientationChecked } func processObjectAttributes(objectAnchor: ARObjectAnchor) { currentObjectAnchor = objectAnchor } } In my View, I am using @ObservedObject to observe the state of these variables, but the error persists when I try to update them during view rendering. Could anyone help me understand why this error occurs and how to avoid it? I understand that state should not be updated during view rendering, but I can’t find a solution that works in this case. Thank you in advance for your help!
Topic: UI Frameworks SubTopic: SwiftUI Tags:
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336
Jan ’25