I am actually a beginner in SwiftUI. I want to know if there is a way to detect when the global position of a View is changing. For the moment I can get the global position of the view with GeometryReader, but I definitely can't detect when it is changing.
Thank you in advance for your help !
struct VideoView: View {
#State var player : AVPlayer // It is a video player
#State var isplaying = false
#State var showcontrols = false // Don't show controls
#State var value : Float = 0
var body: some View {
GeometryReader { geo in
VStack{
ZStack{
VideoPlayer(player: $player)
}
.frame(height: UIScreen.main.bounds.height)
}
.background(Color.black.edgesIgnoringSafeArea(.all))
#IF GLOBAL POSITION OF THIS VIEW IS CHANGING
if(geo.frame(in: .global).midY < 400){
self.player.play()
self.isplaying = true
}
}
#ENDIF
}
}
}
Related
I have the following code for a simple square to which I attach a MagnificationGesture to update its state with a pinch to zoom gesture.
import SwiftUI
struct ContentView2: View {
var scale: CGFloat = 1
var magnificationGesture: some Gesture {
MagnificationGesture()
.onChanged { value in
scale = value
}
}
var body: some View {
VStack {
Text("\(scale)")
Spacer()
Rectangle()
.fill(Color.red)
.scaleEffect(self.scale)
.gesture(
magnificationGesture
)
Spacer()
}
}
}
struct ContentView2_Previews: PreviewProvider {
static var previews: some View {
ContentView2()
}
}
However this simple view behaves weird. When I perform the gesture, the scale #State property is succesfully modified. However when I then do another gesture with my hands, the scale property is reset to its initial state, instead of starting from its current value.
Here is a video of what happens. For example, when the red view is very small, performing the gesture, I would expect that it stays small, instead of completely resetting.
How can I get the desired behaviour - that is - the scale property is not reset
I was able to get it working by adding a bit to the code. Check it out and let me know if this works for your use case:
import SwiftUI
struct ContentView2: View {
var magGesture = MagnificationGesture()
#State var magScale: CGFloat = 1
#State var progressingScale: CGFloat = 1
var magnificationGesture: some Gesture {
magGesture
.onChanged { progressingScale = $0 }
.onEnded {
magScale *= $0
progressingScale = 1
}
}
var body: some View {
VStack {
Text("\(magScale)")
Spacer()
Rectangle()
.fill(Color.red)
.scaleEffect(self.magScale * progressingScale)
.gesture(
magnificationGesture
)
Spacer()
}
}
}
struct ContentView2_Previews: PreviewProvider {
static var previews: some View {
ContentView2()
}
}
I solved it by adding another scale and only updating one of them at the end to keep track of the scale
Code
import SwiftUI
struct ContentView2: View {
#State var previousScale: CGFloat = 1
#State var newScale: CGFloat = 1
var magnificationGesture: some Gesture {
MagnificationGesture()
.onChanged { value in
newScale = previousScale * value
}
.onEnded { value in
previousScale *= value
}
}
var body: some View {
VStack {
Text("\(newScale)")
Spacer()
Rectangle()
.fill(Color.red)
.scaleEffect(newScale)
.gesture(
magnificationGesture
)
Spacer()
}
}
}
struct ContentView2_Previews: PreviewProvider {
static var previews: some View {
ContentView2()
}
}
I am trying to achieve drag and magnification gestures take in place simultaneously. With the code below, I was able to achieve transitioning dragging to magnifying, however, when I release one finger after magnification, the drag gesture is killed even though one finger is still on the rectangle. In the Photos app in iOS, you can magnify and release one finger then you can still drag an image. I have looked at Simultaneous MagnificationGesture and DragGesture with SwiftUI. Has this been fixed since then? If not, is there any way to achieve this by using UIViewRepresentable?
import SwiftUI
struct DragAndMagnificationGestures: View {
#State private var currentAmount = 0.0
#State private var finalAmount = 1.0
#State private var dragGestureOffset: CGSize = .zero
var body: some View {
VStack {
let combined = dragGesture.simultaneously(with: magnificationGesture)
Rectangle()
.frame(width: 200, height: 200)
.scaleEffect(finalAmount + currentAmount)
.offset(dragGestureOffset)
.gesture(combined)
}
}
}
struct MultiGesture_Previews: PreviewProvider {
static var previews: some View {
DragAndMagnificationGestures()
}
}
extension DragAndMagnificationGestures {
private var dragGesture: some Gesture {
DragGesture()
.onChanged { value in
if finalAmount != 0 {
withAnimation(.spring()) {
dragGestureOffset = value.translation
}
}
}
.onEnded({ value in
withAnimation(.spring()) {
dragGestureOffset = .zero
}
})
}
private var magnificationGesture: some Gesture {
MagnificationGesture()
.onChanged { amount in
currentAmount = amount - 1
}
.onEnded({ amount in
finalAmount += currentAmount
currentAmount = 0
})
}
}
i am learning swiftui now and I am newbie for stackoverflow, I find a question,this is my code. I want to change the #State nopubName in sink ,but it's not work,the print is always "Nimar", I don't know why
struct ContentView: View {
#State var nopubName: String = "Nimar"
private var cancellable: AnyCancellable?
var stringSubject = PassthroughSubject<String, Never>()
init() {
cancellable = stringSubject.sink(receiveValue: handleValue(_:))
}
func handleValue(_ value: String) {
print("handleValue: '\(value)'")
self.nopubName = value
print("in sink "+nopubName)
}
var body: some View {
VStack {
Text(self.nopubName)
.font(.title).bold()
.foregroundColor(.red)
Spacer()
Button("sink"){
stringSubject.send("World")
print(nopubName)
}
}
}
}
You should only access a state property from inside the view’s body, or from methods called by it.
https://developer.apple.com/documentation/swiftui/state
You can get that functionality working in an ObservableObject and update an #Published To keep the UI updated
https://developer.apple.com/documentation/swiftui/managing-model-data-in-your-app
You don't need to use Combine, If you are within the View, you can change the value of #State variables directly
struct ContentView: View {
#State var nopubName: String = "Nimar"
var body: some View {
VStack {
Text(self.nopubName)
.font(.title).bold()
.foregroundColor(.red)
Spacer()
Button("sink"){
nopubName = "World"
}
}
}
}
Revised Example
Based on the thoughtful response from #pawello2222 I received in the comments below I have revised an example to demonstrate the issue I am wrestling with.
In order to demonstrate the issue I am having I am using 2 views a parent and a child. In my code code the parent view executes multiple steps but sometimes the animation subview is not visible in the first step. However when it does become visible the animation has already taken on the appearance of the end state. You can see this behavior in the following example.
Parent View
struct ContentView: View {
#State var firstTime = true
#State var breath = false
var body: some View {
VStack {
// This subview is not displayed until after the first time
if !firstTime {
SecondView(breath: $breath)
}
Spacer()
// A button click simulates the steps in my App by toggling the #Binding var
Button("Breath") {
withAnimation {
self.breath.toggle()
self.firstTime = false
}
}
// This vies shows what happens when the subview is being displayed with an intial state of false for the #Binding var
Spacer()
SecondView(breath: $breath)
}
}
}
Here is the subview containing the animation and using a #Binding var to control the animation appearance.
struct SecondView: View {
#Binding var breath: Bool
var body: some View {
Image(systemName: "flame")
.resizable()
.rotationEffect(.degrees(breath ? 360 : 0), anchor: .center)
.scaleEffect(breath ? 1 : 0.2)
.opacity(breath ? 1 : 0.75)
.animation(.easeInOut(duration: 2))
.foregroundColor(Color.red)
}
}
When you execute this the first time thru the top subview is not being displayed and when you click the button the lower subview executes the expected animation and then toggles the firstTime var so that the top subview becomes visible. Notice that the animation is fully expanded and if I was to then have another step (click) with the same value of true for the #Binding property the view would not change at all. This is the issue I am wrestling with. I would like to keep the subview from being at the end state if the first step is one that has toggled the Bool value even if the subview was not being displayed. In other words I would like to only initialize the subview when it is actually being displayed with a value of true so that the animation will always start out small.
This is why I was hoping to have the subview initialized the Binding var to false until it actually gets invoked for the first time (or to reset its state to the shrunk version of the animation) whichever is more feasible.
It looks like you may want to initialise _breath with the provided parameter:
struct ContentView: View {
#Binding var breath: Bool
init(breath: Binding<Bool>) {
_breath = breath
}
}
However, if you want to use a constant value (in your example false) you can do:
struct ContentView: View {
#Binding var breath: Bool
init(breath: Binding<Bool>) {
_breath = .constant(false)
}
}
But then, why do you need the breath: Binding<Bool> parameter?
EDIT
Here is an example how to control an animation of a child view using a #Binding variable:
struct ContentView: View {
#State var breath = false
var body: some View {
VStack {
Button("Breath") {
withAnimation {
self.breath.toggle()
}
}
SecondView(breath: $breath)
}
}
}
struct SecondView: View {
#Binding var breath: Bool
var body: some View {
Image(systemName: "flame")
.imageScale(.large)
.rotationEffect(.degrees(breath ? 360 : 0), anchor: .center)
.scaleEffect(breath ? 1 : 0.2)
.opacity(breath ? 1 : 0.75)
.animation(.easeInOut(duration: 2))
}
}
How is it possible to set a #State var inside a geometryReader?
This is my code:
#State var isTest:Int = 0
var body: some View {
VStack{
ForEach(self.test, id: \.id) { Test in
VStack{
GeometryReader { geometry in
self.isTest = 1
I try with a function but it doesn't work.
#State var isTest: Int = 0
func testValue() {
self.isTest = 1
}
var body: some View {
VStack{
ForEach(self.test, id: \.id) { Test in
VStack{
GeometryReader { geometry in
testValue()
Any idea? Thanks!
I also had a similar problem yesterday. But I was trying to pass a value from inside the GeometryReader.
I tried a couple of ways but it didn't work.
When I use #State var to declare the variable, the compiler again complained in a purple line saying that Modifying the view during update will make it become Undefined.
When I tried to declare a variable using var only, the compiler just told me that it's immutable.
And then, I tried storing it onto my #EnvironmentObject. And I just got a dead loop.
So, my last hope was using the notification way and some how it worked. But I don't know if it's the standard way of implementation.
#State private var viewPositionY:CGFloat = 0
First, post the value frame.origin.y via notification.
GeometryReader{ geometry -> Text in
let frame = geometry.frame(in: CoordinateSpace.global)
NotificationCenter.default.post(name: Notification.Name("channelBlahblahblah"), object:nil, userInfo:["dict":frame.origin.y])
return Text("My View Title")
}
And then declare a publisher to receive the notification.
private let myPublisher = NotificationCenter.default.publisher(for: Notification.Name("channelBlahblahblah"))
Finally, use the the .onReceive modifier to receive the notification.
.onReceive(myPublisher) { (output) in
viewPositionY = output.userInfo!["dict"] as! CGFloat
//you can do you business here
}
While putting code into function is a nice touch, there may arrive another problem and that is altering the #State variable during update phase:
[SwiftUI] Modifying state during view update, this will cause undefined behavior
Using NotificationCenter to move #State variable update after view update phase can help, but one could use much more simple solution like performing variable update right after render phase by using DispatchQueue.
#State var windowSize = CGSize()
func useProxy(_ geometry: GeometryProxy) -> some View {
DispatchQueue.main.async {
self.windowSize = geometry.size
}
return EmptyView()
}
var body: some View {
return GeometryReader { geometry in
self.useProxy(geometry)
Text("Hello SwiftUI")
}
}
You can update #State variables in the onAppear method if you need the initial geometry values
#State var windowSize = CGSize()
var body: some View {
return GeometryReader { geometry in
VStack {
Text("Hello SwiftUI")
}
.onAppear {
windowSize = geometry.size
}
}
}
You can use onAppear(perform:) to update #State variables with the initial view size and onChange(of:perform:) to update the variables when the view size changes:
struct MyView: View {
#State private var size: CGSize = .zero
var body: some View {
GeometryReader { geometry in
ZStack {
Text("Hello World")
}.onAppear {
size = geometry.size
}.onChange(of: geometry.size) { newSize in
size = newSize
}
}
}
}
Try this
#State private var viewSize: CGSize = .zero
var body: some View {
VStack {
// ...
}
.background(GeometryReader { proxy in
Color.clear.preference(
key: ViewSizePreferenceKey.self,
value: proxy.size
)
})
.onPreferenceChange(ViewSizePreferenceKey.self) { size in
viewSize = size
}
}
private struct ViewSizePreferenceKey: PreferenceKey {
static var defaultValue: CGSize = .zero
static func reduce(value: inout CGSize, nextValue: () -> CGSize) {
value = value.width + value.height > nextValue().width + nextValue().height ? value : nextValue()
}
}
So it's totally possible to update a #State inside a GeometryReader. The solution is simple. However, there's a caveat:
you might end up with an infinite loop
(nothing too troublesome, I'll present a solution here)
You'll just need a DispatchQueue.main.async and explicitly declare the type of the view inside GeometryReader. If you execute the View below (don't forget to stop it) you'll see that it never stops updating the value of the Text.
NOT THE FINAL SOLUTION:
struct GenericList: View {
#State var timesCalled = 0
var body: some View {
GeometryReader { geometry -> Text in
DispatchQueue.main.async {
timesCalled += 1 // infinite loop
}
return Text("\(timesCalled)")
}
}
}
This happens because the View will "draw" the GeometryReader, which will update a #State of the View. Thus, the new #State invalidates the View causing the View to be redrawn. Consequently going back to the first step (drawing the GeometryReader and updating the state).
To solve this you need to put some constraints in the draw of the GeometryReader. Instead of returning your View inside the GeometryReader, draw it then add the GeometryReader as a transparent overlay or background. This will have the same effect but you'll be able to put constraints in the presentation.
Personally, I'd rather use an overlay because you can add as many as you want. Note that an overlay does not permit an if else inside of it, but it is possible to call a function. That's why there's the func geometryReader() below. Another thing is that in order to return different types of Views you'll need to add #ViewBuilder before it.
In this code, the GeometryReader is called only once and you get the #State var timesCalled updated.
FINAL SOLUTION:
struct GenericList: View {
#State var timesCalled = 0
#ViewBuilder
func geometryReader() -> some View {
if timesCalled < 1 {
GeometryReader { geometry -> Color in
DispatchQueue.main.async {
timesCalled += 1
}
return Color.clear
}
} else {
EmptyView()
}
}
var body: some View {
Text("\(timesCalled)")
.overlay(geometryReader())
}
}
Note: you don't need to put the same constraints, for example, in my case, I wanted to move the view with the drag gesture. So, I've put the constraints to start when the user touches down and to stop when the user ends the drag gesture.