I'm looking for an event in the life-cycle of a view in SwiftUI, that is equivalent to viewWillAppear().
Yes, I know there is an ".OnAppear" in SwiftUI, but that is like viewDidAppear.
Is there a workaround to do get that specific execution time before view is loaded?
Try this modifier:
.onReceive(NotificationCenter.default.publisher(for: UIApplication.willEnterForegroundNotification)) { _ in
// your code
}
Related
I have question about wrapping custom UIViewControllers into SwiftUI view using UIViewControllerRepresentable. Does anyone have issue with UITextFields in such case?
I have situation that sometimes this textfield works normally when wrapped and otherwise they just work for a while and stopped working after editinig text for about 10sec or hiding/showing keyboard, or they doesn't work at all.
Situation seems to be very odd.
Ok it was the problem with
override var canBecomeFirstResponder: Bool { true }
on UIViewController
https://developer.apple.com/documentation/uikit/uiresponder/1621130-canbecomefirstresponder
In UIKit we can use GCEventViewController to intercept the game controllers from propagating Home button presses to the responders (and have them quit our app) by setting controllerUserInteractionEnabled = false
SwiftUI Apps do not use ViewControllers, so, except for resurrecting one to embed the whole app in it, we can't use the above solution to avoid the player leaving out game / app by accident by pressing the wrong button (not can we use buttonB)
Does anyone know a solution to this conundrum? Did Apple already implement a new way to intercept high-level events so we can deal with them internally?
Thanks!
You have to have a focusable view (like a button) and then you can use onExitCommand in the containing view to simply ignore the exit event, or do something different.
struct ContentView: View {
var body: some View {
VStack {
Button("Hello, world!") {
}
}.onExitCommand {
// Do nothing
}
}
}
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)
}
}
In UIKit-based application we can have custom navigation transitions using UIViewControllerAnimatedTransitioning protocol.
Is there an equivalent in SwiftUI?
I know we can already animate between removing and adding views.
But how do we do this when we push and pop to the navigation stack?
There isn't anything like this available in SwiftUI's APIs so far afaik. Make sure to open an enhancement request with Apple.
Implementing "navigation" on your own is a terrible idea, as you basically give all the accessibility and facility support afforded by UINavigationController.
Instead, here is a suggestion:
Either by means of a custom SwiftUI view or modifier, wrap the NavigationView with a UIViewControllerRepresentable wrapper, which in turn sets up a UIHostingController subclass, which waits for addChild(_:) to be called, which will be the navigation controller added as a child of the hosting controller. From here, if your animations are "static" (e.g. do not require any subview to subview transition), you can accomplish this here by implementing the navigation controller delegate, and providing the animation controller.
If you do need more evolved transitions (such as Photos.app's photo transition), you can create a custom UIViewRepresentable wrapper, which will serve as markers for "from" views and "to" views, you can then use those discover in UIKit, and e.g. can snapshot and animate in transitions.
Proposed API can look like this:
struct ContentView1: View {
var body: some View {
NavigationLink(destination: DetailView()) {
Image("small").customSourceTarget()
}.navigationBarTitle("Navigation")
}
}
struct ContentView2: View {
var body: some View {
Image("large").customTransitionTarget()
}
}
NavigationView {
ContentView1()
}.customAnimatable()
I'm building an Apple Watch app, and there is code I want to run every time the app is brought to the foreground.
Previously, if I wanted to do this in a watchOS with a WKInterfaceController, I would put this code in didAppear().
In SwiftUI, there is onAppear(), but when I call that on watchOS it only seems to be called the first time the app loads up, so it behaves like WKInterfaceController.willActivate() instead. The app has just a single view.
If onAppear() is the equivalent of WKInterfaceController.willActivate(), is there a different SwiftUI function that is the equivalent of WKInterfaceController.didAppear()?
Here's my current example code:
import SwiftUI
struct ContentView: View {
var body: some View {
Text("Hello World").font(.footnote)
.onAppear {
print("onAppear called")
}
}
}
In the meantime, I am going to experiment with triggering what I need to do within the ExtensionDelegate, but I'm just trying to learn my way around SwiftUI on WatchOS, so knowing the answer to this would be helpful in the future.