How to make a view gone in swiftui - swift

I was trying to hide view but noticed that view.hidden() will only hide the view but but the space remains.
I also tried some of the suggestions on this link Dynamically hiding view in SwiftUI
But it didn't really work for me, albeit it was a starting point.
Find below what I finally did.

Here's an approach without an extension.
struct ContentView: View {
#State var hidden = false
#State var text = ""
var body: some View {
NavigationView {
List {
Section {
Toggle("Hide", isOn: $hidden.animation(Animation.easeInOut))
}
if !hidden {
Section {
TextField("Pin", text: $text)
}
}
}
}
}
}

I created an extension function as below
extension View {
#ViewBuilder func hiddenConditionally(isHidden: Binding<Bool>) -> some View {
isHidden.wrappedValue ? self : self.hidden() as? Self
}
}
and you can call it as below
TextField("Pin", text: $pin)
.hiddenConditionally(isHidden: $showPinField)

Related

SwiftUI macOS NavigationView - onChange(of: Bool) action tried to update multiple times per frame

I'm seeing onChange(of: Bool) action tried to update multiple times per frame warnings when clicking on NavigationLinks in the sidebar for a SwiftUI macOS App.
Here's what I currently have:
import SwiftUI
#main
struct BazbarApp: App {
#StateObject private var modelData = ModelData()
var body: some Scene {
WindowGroup {
ContentView()
.environmentObject(modelData)
}
}
}
class ModelData: ObservableObject {
#Published var myLinks = [URL(string: "https://google.com")!, URL(string: "https://apple.com")!, URL(string: "https://amazon.com")!]
}
struct ContentView: View {
#EnvironmentObject var modelData: ModelData
#State private var selected: URL?
var body: some View {
NavigationView {
List(selection: $selected) {
Section(header: Text("Bookmarks")) {
ForEach(modelData.myLinks, id: \.self) { url in
NavigationLink(destination: DetailView(selected: $selected) ) {
Text(url.absoluteString)
}
.tag(url)
}
}
}
.onDeleteCommand {
if let selected = selected {
modelData.myLinks.remove(at: modelData.myLinks.firstIndex(of: selected)!)
}
selected = nil
}
Text("Choose a link")
}
}
}
struct DetailView: View {
#Binding var selected: URL?
var body: some View {
if let selected = selected {
Text("Currently selected: \(selected)")
}
else {
Text("Choose a link")
}
}
}
When I alternate clicking on the second and third links in the sidebar, I eventually start seeing the aforementioned warnings in my console.
Here's a gif of what I'm referring to:
Interestingly, the warning does not appear when alternating clicks between the first and second link.
Does anyone know how to fix this?
I'm using macOS 12.2.1 & Xcode 13.2.1.
Thanks in advance
I think the issue is that both the List(selection:) and the NavigationLink are trying to update the state variable selected at once. A List(selection:) and a NavigationLink can both handle the task of navigation. The solution is to abandon one of them. You can use either to handle navigation.
Since List look good, I suggest sticking with that. The NavigationLink can then be removed. The second view under NavigationView is displayed on the right, so why not use DetailView(selected:) there. You already made the selected parameter a binding variable, so the view will update if that var changes.
struct ContentView: View {
#EnvironmentObject var modelData: ModelData
#State private var selected: URL?
var body: some View {
NavigationView {
List(selection: $selected) {
Section(header: Text("Bookmarks")) {
ForEach(modelData.myLinks, id: \.self) { url in
Text(url.absoluteString)
.tag(url)
}
}
}
.onDeleteCommand {
if let selected = selected {
modelData.myLinks.remove(at: modelData.myLinks.firstIndex(of: selected)!)
}
selected = nil
}
DetailView(selected: $selected)
}
}
}
I can recreate this problem with the simplest example I can think of so my guess is it's an internal bug in NavigationView.
struct ContentView: View {
var body: some View {
NavigationView {
List {
NavigationLink("A", destination: Text("A"))
NavigationLink("B", destination: Text("B"))
NavigationLink("C", destination: Text("C"))
}
}
}
}

AnyView blocks View updates

I have a simple view:
This view is wrapped by another view that has an observed object.
Such code doesn't update the view:
struct SomeView: View {
#ObservedObject var viewModel: ViewModel
var body: some View {
let text = viewModel.text
return ForEach(0..<1) { AnyView(text) }
}
}
but it works:
return ForEach(0..<1) { text }
Is it bug? Can I use AnyView for ForEach view?
Oh, when I asked a question I found a solution:
You should use ForEach ForEach(0..<1, id: \.self) { AnyView(text) }

Why does modifying the label of a NavigationLink change which View is displayed in SwiftUI?

I have an #EnvironmentObject called word (of type Word) whose identifier property I'm using for the label of a NavigationLink in SwiftUI. For the DetailView that is linked to the NavigationLink, all I have put is this:
struct DetailView: View {
#EnvironmentObject var word: Word
var body: some View {
VStack {
Text(word.identifier)
Button(action: {
self.word.identifier += "a"
}) {
Text("Click to add an 'a' to Word's identifier")
}
}
}
}
The ContentView that leads to this DetailView looks like this (I've simplified my actual code to isolate the problem).
struct ContentView: View {
#EnvironmentObject var word: Word
var body: some View {
NavigationView {
NavigationLink(destination: DetailView()) {
Text(word.identifier)
}
}
}
}
When I tap the button on the DetailView, I'd expect it to update the DetailView with a new word.identifier that has an extra "a" appended onto it. When I tap it, however, it takes me back to the ContentView, albeit with an updated word.identifier. I can't seem to find a way to stay on my DetailView when the word.identifier being used by the ContentView's NavigationLink is modified. Also, I am running Xcode 11.3.1 and am currently unable to update, so if this is has been patched, please let me know.
Here is workaround solution
struct DetailView: View {
#EnvironmentObject var word: Word
#State private var identifier: String = ""
var body: some View {
VStack {
Text(self.identifier)
Button(action: {
self.identifier += "a"
}) {
Text("Click to add an 'a' to Word's identifier")
}
}
.onAppear {
self.identifier = self.word.identifier
}
.onDisappear {
self.word.identifier = self.identifier
}
}
}
This works as expected on iOS 13.4, assuming Word is something like:
class Word : ObservableObject {
#Published var identifier = "foo"
}

Value from #State variable does not change

I have created a View that provides a convinient save button and a save method. Both can then be used inside a parent view.
The idea is to provide these so that the navigation bar items can be customized, but keep the original implementation.
Inside the view there is one Textfield which is bound to a #State variable. If the save method is called from within the same view everthing works as expected. If the parent view calls the save method on the child view, the changes to the #State variable are not applied.
Is this a bug in SwiftUI, or am I am missing something? I've created a simple playbook implementation that demonstrates the issue.
Thank you for your help.
import SwiftUI
import PlaygroundSupport
struct ContentView: View {
// Create the child view to make the save button available inside this view
var child = Child()
var body: some View {
NavigationView {
NavigationLink(
destination: child.navigationBarItems(
// Set the trailing button to the one from the child view.
// This is required as this view might be inside a modal
// sheet, and we need to add the cancel button as a leading
// button:
// leading: self.cancelButton
trailing: child.saveButton
)
) {
Text("Open")
}
}
}
}
struct Child: View {
// Store the value from the textfield
#State private var value = "default"
// Make this button available inside this view, and inside the parent view.
// This makes sure the visibility of this button is always the same.
var saveButton: some View {
Button(action: save) {
Text("Save")
}
}
var body: some View {
VStack {
// Simple textfield to allow a string to change.
TextField("Value", text: $value)
// Just for the playground to change the value easily.
// Usually it would be chnaged through the keyboard input.
Button(action: {
self.value = "new value"
}) {
Text("Update")
}
}
}
func save() {
// This always displays the default value of the state variable.
// Even after the Update button was used and the value did change inside
// the textfield.
print("\(value)")
}
}
PlaygroundPage.current.setLiveView(ContentView())
I think a more SwiftUi way of doing it:
import SwiftUI
import PlaygroundSupport
struct ContentView: View {
var body: some View {
return NavigationView {
// tell the child view where to render it's navigation item
// Instead of configuring navigation items.
NavigationLink(destination: Child(navigationSide: .left)) {
Text("Open")
}
}
}
}
struct Child: View {
enum NavigationSide { case left, right }
// If you really want to encapsulate all state in this view then #State
// is a good choice.
// If the parent view needs to read it, too, #Binding would be your friend here
#State private var value: String = "default"
// no need for #State as it's never changed from here.
var navigationSide = NavigationSide.right
// wrap in AnyView here to make ternary in ui code easier readable.
var saveButton: AnyView {
AnyView(Button(action: save) {
Text("Save")
})
}
var emptyAnyView: AnyView { AnyView(EmptyView()) }
var body: some View {
VStack {
TextField("Value", text: $value)
Button(action: {
self.value = "new value"
}) {
Text("Update")
}
}
.navigationBarItems(leading: navigationSide == .left ? saveButton : emptyAnyView,
trailing: navigationSide == .right ? saveButton : emptyAnyView)
}
func save() {
print("\(value)")
}
}
TextField will only update your value binding when the return button is pressed. To get text changes that occur during editing, set up an observed object on Child with didSet. This was the playground I altered used from your example.
struct ContentView: View {
var child = Child()
var body: some View {
NavigationView {
NavigationLink(
destination: child.navigationBarItems(
trailing: child.saveButton
)
) {
Text("Open")
}
}
}
}
class TextChanges: ObservableObject {
var completion: (() -> ())?
#Published var text = "default" {
didSet {
print(text)
}
}
}
struct Child: View {
#ObservedObject var textChanges = TextChanges()
var saveButton: some View {
Button(action: save) {
Text("Save")
}
}
var body: some View {
VStack {
TextField("Value", text: $textChanges.text).multilineTextAlignment(.center)
Button(action: {
print(self.textChanges.text)
}) {
Text("Update")
}
}
}
func save() {
print("\(textChanges.text)")
}
}
PlaygroundPage.current.setLiveView(ContentView())
Inside Child: value is mutable because it's wrapped with #State.
Inside ContentView: child is immutable because it's not wrapped with #State.
Your issue can be fixed with this line: #State var child = Child()
Good luck.
Child view needs to keep its state as a #Binding. This works:
import SwiftUI
import PlaygroundSupport
struct ContentView: View {
#State var v = "default"
var body: some View {
let child = Child(value: $v)
return NavigationView {
NavigationLink(
destination: child.navigationBarItems(trailing: child.saveButton)
) {
Text("Open")
}
}
}
}
struct Child: View {
#Binding var value: String
var saveButton: some View {
Button(action: save) {
Text("Save")
}
}
var body: some View {
VStack {
TextField("Value", text: $value)
Button(action: {
self.value = "new value"
}) {
Text("Update")
}
}
}
func save() {
print("\(value)")
}
}
PlaygroundPage.current.setLiveView(ContentView())
Based on this commend from #nine-stones (thank you!) I implemented a more SwiftUI way so solve my problem. It does not allow the customization of the navigation items as I planned, but that was not the problem that needed to be solved. I wanted to use the Child view in a navigation link, as well as inside a modal sheet. The problem was how to perform custom cancel actions. This is why I removed the button implementation and replaced it with a cancelAction closure. Now I can display the child view wherever and however I want.
One thing I still do not know why SwiftUI is not applying the child context to the button inside the saveButton method.
Still, here is the code, maybe it helps someone in the future.
import SwiftUI
import PlaygroundSupport
struct ContentView: View {
#Environment(\.presentationMode) var presentationMode
var body: some View {
NavigationView {
NavigationLink(
destination: Child(
// Instead of defining the buttons here, I send an optional
// cancel action to the child. This will make it possible
// to use the child view on navigation links, as well as in
// modal dialogs.
cancelAction: {
self.presentationMode.wrappedValue.dismiss()
}
)
) {
Text("Open")
}
}
}
}
struct Child: View {
// Store the value from the textfield
#State private var value = "default"
#Environment(\.presentationMode) var presentationMode
var cancelAction: (() -> Void)?
// Make this button available inside this view, and inside the parent view.
// This makes sure the visibility of this button is always the same.
var saveButton: some View {
Button(action: save) {
Text("Save")
}
}
var body: some View {
VStack {
// Simple textfield to allow a string to change.
TextField("Value", text: $value)
// Just for the playground to change the value easily.
// Usually it would be chnaged through the keyboard input.
Button(action: {
self.value = "new value"
}) {
Text("Update")
}
}
.navigationBarItems(
leading: self.cancelAction != nil ? Button(action: self.cancelAction!, label: {
Text("Cancel")
}) : nil,
trailing: self.saveButton
)
}
func save() {
// This always displays the default value of the state variable.
// Even after the Update button was used and the value did change inside
// the textfield.
print("\(value)")
}
}
PlaygroundPage.current.setLiveView(ContentView())

SwiftUI: Animate Cells within a Form

I am trying to animate my Form or rather the cells within it. My problem is that the following code give me a nice insertion animation but for the removal the cell is suddenly removed after am ugly looking delay.
import SwiftUI
struct ContentView: View {
#State var toggledValue = false
#State var pickedValue = 0
var body: some View {
NavigationView {
Form {
Section {
Toggle(isOn: $toggledValue) {
Text("Toggled Value")
}
if toggledValue {
Picker(selection: $pickedValue, label: Text("Picked Value")) {
ForEach((0...5).identified(by: \.self)) {
Text("Pick Value \($0)").tag($0)
}
}
}
}
Section {
Text("Some Text")
}
}
.navigationBarTitle("Navigation Bar Title")
}
}
}
What I tried so far is to to wrap the Toggle in a withAnimation closure but this does not change anything. What makes me wondering is that the same code using List instead of Form gives me the expected Animation. Is that a bug or am I overseeing something?
This will probably work (tested in iOS 16 in a similar situation):
Add #State private var isShowingPicker = false
Replace if toggledValue by if isShowingPicker
Under .navigationBarTitle(...) add:
onChange(of: toggledValue)
{ newValue in
withAnimation { isShowingPicker = newValue }
}