I need to move the accessibility focus to certain element on the screen. In UIKit, we can simply do UIAccessibility.post(.screenChanged, element)
However, when I do that with a SwiftUI View, the app crashes with the following message in console
This class '__SwiftValue' is not a known serializable element and returning it as an accessibility element may lead to crashes
Any idea how we can move focus to certain elements on the screen in SwiftUI?
A workaround would be: Post a notification when the UIView appears:
.onAppear(perform: {
DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
UIAccessibility.post(notification: .screenChanged, argument: "New Screen")
}
})
As argument it would make sense to put in the text of the accessibility label of the desired view. The impaired user would just not know where the screenReader is focusing if the user could recognize the white surrounding of the screenReader focus.
To make things smooth the delay of 0.1 should be adapted while testing with different languages.
Related
Basic question: how can I prevent a SwiftUI subview to redraw when the parent redraws?
I am experiencing performance issues on my project because so many nested views are constantly redrawn. Now, so of them are redrawn without anything being changed. To debug my problem, I even tried to simplify the problem to its core:
struct StupidView: View {
init() {
print("redraw")
}
var body: some View {
ZStack{}
}
}
This empty view, of course, does not have any moving part that requires redrawing, but it gets redrawn every time its parent is redrawn.
I even tried to add a .id(1) to it with no results. Of course, my problem is with complex views whose useless redrawing slows down the app. How to not redraw parts of a view?
Initializing a View has no meaning of rendering!
It does not rendered but got initialized try this down code, in SwiftUI initializing a View is pretty normal thing! A View could get Initializied 100 times but it will rendered if it needs! if your View has complex Content that SwiftUI get confused we can help SwiftUI in this way that make our View Equatable, then SwiftUI will understand when really need to rendered!
struct StupidView: View {
init() {
print("initializing!")
}
var body: some View {
print("rendering!")
return ZStack{}
}
}
My problem is SecureField in SwiftUI doesn’t display characters input by the user for any time at all, it just directly shows the '•' symbol for each character as it's typed - whereas in UIKit, UITextField (with isSecureTextEntry = true) shows the latest character for a second before hiding it behind '•'.
UX testers at my company have requested I bring back the "old behaviour" - but this behaviour doesn't seem part of any public API.
Interestingly this goes for UITextField custom classes injected into SwiftUI using UIViewRepresentable too - they behave in the "SwiftUI way" described above. So there's some contextual behaviour modification going on in SwiftUI for all secure UITextField behaviour? I'd have to completely rewrite my SwiftUI form into a full UIViewController to get back the behaviour (modally pushed UIViewControllers with secure UITextFields do exhibit the desired behaviour.)
Is this a sort of sideline bug in SwiftUI? I see the same thing for SwiftUI in both iOS13 and 14. Anyone seen a workaround or solution?
-EDIT-
After #Asperi's great explanation below, I noticed that my UITextField custom classes injected into SwiftUI using UIViewRepresentable were forcing this behaviour by unnecessarily setting the text binding in the updateUIView call. Using a Coordinator only to deal with text logic fixed the problem for me when using this method.
The observed effect is due to immediate apply to bound string state and immediate react/rebuild of view.
To bring desired behavior beck we need to postpone somehow state update and thus give a chance for SecuredField/UITextField to update self without synchronisation with state.
Here is a demo of possible direction (it is not ideal, but a way to go). Tested with Xcode 12.1 / iOS 14.1.
struct DemoSecureFieldView: View {
#State private var password = "demo"
var textBinding: Binding<String> {
Binding(get: { password },
set: { value in
// more logic can be added to delay _only_ if new symbol added,
// and force apply if next symbol came fast
DispatchQueue.main.asyncAfter(deadline: .now() + 0.25) {
password = value
}
}
)
}
var body: some View {
VStack {
SecureField("Placeholder", text: textBinding)
.textFieldStyle(RoundedBorderTextFieldStyle())
.padding()
}.background(Color.pink)
}
}
I have the following code example:
struct ContentView: View {
#State var showText = true
var body: some View {
VStack {
if self.showText {
Text("Hello")
}
//else {
// EmptyView()
// }
}
}
}
When it runs I get the text showing as normal. However, if I set showText to false it still compiles and runs as normal even though the VStack contains nothing - it just doesn't show anything when run. If I uncomment the else clause the example also runs as expected. If I remove all the contents of the VStack however, the example won't compile as nothing is returned.
So my questions are:
Is SwiftUI silently adding an EmptyView when nothing is in the VStack when showText is false ?
Should I really be adding the else clause and return an EmptyView ?
The question isn't completely academic either as I have a use case where I would prefer the whole view to be more or less 'thrown away' rather than have EmptyViews in the hierarchy, though my understanding of SwiftUI is pretty limited at the moment so it may not matter.
VStack is a function builder so it expects to get some value back from the closure. In the case of the if it invokes the buildEither version of the function builder so that satisfies the condition that its not empty. See the function builder proposal. Any ways you should not worry about the EmptyViews. A SwiftUI.View is just a blue print to build the actual view (as apple calls it a cheap value on the stack). It is not the real view object in memory and on the graphics card, as with a UIView or CALayer. The rendering system is going to translate your EmptyView into a noop. SwiftUI.Views get created and discarded all the time and are designed to be cheap unlike UIViews, and the system diff's the SwiftUI.View tree and only applies the delta to the real views in graphics memory similarl to how Flutter, React, and Android Compose work.
So I'm making a button for a "New Note" in Swift UI similar to the Apple Notes app.
Right now my "New Button" is a "Navigation Link" like so:
NavigationLink(
destination: EditorView(makeNewNote())
) {
Text("New")
}
Unfortunately—this triggers my app to create a new note every time the view loaded. :(
:/
I've been looking for a way to initate a segue on button push but I'm not finding success on this yet.
When I tried a modal—I found myself having the same problem
Button("New") {
self.isNew = true
}.sheet(isPresented: $isNew, content: {
EditorView(makeNewNote())
})
I'm wondering what the best way to approach this would be.
Having no success :(
Edit:
I referred to this and the documentation but I haven’t found a way to segue via a button push which would be ideal. (The function dosent get triggered in the closure :)
https://www.hackingwithswift.com/quick-start/swiftui/how-to-push-a-new-view-onto-a-
Also...if you were curious what makeNewButton() does—it basically inserts a new Core Data object into my app’s managed context.
I'm not entirely sure, but it kinda sounds like to me your problem lies in your model. Because each time your View loads it calls the makeNewButton() function right?
Maybe you can fix the problem by displaying the "new note" view and having an extra "Save" button that only makes changes to your model once it's triggered.
Alternatively, you could use context.rollback() to discard changes. Also, check out this Project. It's Beta 4 but works just the same and imo is a good example how to use CoreData with SwiftUI. :)
Swift 3/iOS 10/Xcode 8
I have a view controller (pieChart) that contains a label, two buttons and an empty view (which will contain a pie chart). The label and two buttons are incorporated into a horizontal stack view, which lies above the pie chart view.
The above VC is embedded into one of four container views (The main screen of the app is comprised of these four container views) when the app starts up.
In pieChart, I have linked both buttons up to their respective IBActions and IBOutlets. When clicking on button 2, a modal segue should occur to another VC but this does not happen. Visibly, the button is registering the click - ie it changes colour when you click it. I have placed a print statement in the IBAction method for button 2 but this too does not display. No error messages are displayed in console either.
The only reasons for this occurring that I have found after several hours of hunting are:
sub views have been added to the button itself so the click event signal passes by the button to be received by the added sub views. This is not the case for me. Order is Main App Window > Container View > Embedded VC > Stack View > Button. InteractionEnabled is set to true for all.
Button lies partially outside containing view (it's height/width might be greater than its containing view). This is not the case for me. The stack view, label and both buttons share the same height and the width of the stack view is equal to the sum of the widths of the label and buttons plus the spacing between the label and buttons.
I have also tried adding an event handler programmatically with:
SelectAnalyisButtonOutlet.addTarget(self, action: #selector(SelectAnalysisButtonClicked), for: .touchUpInside)
but the same outcome occurs.
Are there any other reasons for the click events seemingly not registering?
EDIT 1
The pieChart VC mentioned above is one of several VC's that are swapped out of the same container view (called detailContainerView), depending on which button (all of which work just fine) is clicked in one of the OTHER container views (called TabBar).
I placed a button in each of two other VC's that get displayed in detailContainerView and hooked them each up to an IBAction. Each IBAction contains a print statement that fires when the button is clicked. At the moment then, these two VC's only consist of a label and the newly inserted buttons. None of the buttons worked when I ran the app.
I then set one of the VC's of detailContainerView as the Initial View Controller in the Attributes Inspector and re-ran the app. Suddenly the buttons now work! If I then hook the buttons up to a segue, the segues work too!
Something seems to change when I swap out the VC's in detailContainerView. The code I am using to swap the VC's out is as follows:
func SwapOutControllers(vc: UIViewController, vcName: String){
//REMOVE OLD VC
detailPaneVCReference?.willMove(toParentViewController: nil)
detailPaneVCReference?.view.removeFromSuperview()
detailPaneVCReference?.removeFromParentViewController()
var newVc: UIViewController?
switch vcName {
case "Biography":
newVc = vc as! Biography
case "Social Media":
newVc = vc as! SocialMedia
case "News Feed":
newVc = vc as! NewsFeeds
case "Stats":
newVc = vc as! StatsAboutParliament
case "Petitions":
newVc = vc as! Petitions
default:
print("Error: No VC Found!")
}
//ADD NEW VC
ParentVC?.addChildViewController(newVc!)
let width = detailContainerView?.frame.width
let height = detailContainerView?.frame.height
newVc?.view.frame = CGRect(x: 0, y: 0, width: width!, height: height!)
detailContainerView?.addSubview((newVc?.view)!)
newVc?.didMove(toParentViewController: ParentVC)
}
detailPaneVCReference is a reference to whichever VC is currently being displayed by detailContainerView. ParentVC is the VC that contains the four container views.
The VC that is removed from the ParentVC still exists in the debugging view hierarchy after it has been removed/swapped out - could this be somehow blocking the click event from reaching the event handler?
SOLUTION!
The source of my problem has been that the references I had made to each of the view controllers that get swapped in and out of detailContainerView were incorrectly declared as weak references. I deleted "weak" (eg "weak var x: UIViewController?" --> "var x: UIViewController?") from each of the declarations and voila!, the code now works as intended!
The source of my problem has been that the references I had made to each of the view controllers that get swapped in and out of detailContainerView were incorrectly declared as weak references. I deleted "weak" (eg "weak var x: UIViewController?" --> "var x: UIViewController?") from each of the declarations and voila!, the code now works as intended!