Swiftui animation calendar dates - ios

Question

In my app I want to show the passage of time by having a "calendar" transition from one date to the next, to the next, to the next, etc. So, for example, if I want to show the date transitioning from the 18th, to the 19th, to the 20th, I will show 18 for 1 second, then fade that out, fade in 19, fade that out, then fade in 20.
I have the following to show one date animating to the next (e.g. 18 > 19th):
struct Calendar: View {
#State var date: String
var body: some View {
VStack {
Spacer()
ZStack {
RoundedRectangle(cornerRadius: 20)
.stroke(Color.black, lineWidth: 2)
.frame(width: 200, height: 200)
RoundedRectangle(cornerRadius: 20)
.fill(Color.red)
.frame(width: 200, height: 200)
.offset(y: 160)
.clipped()
.offset(y: -160)
RoundedRectangle(cornerRadius: 20)
.stroke(Color.black, lineWidth: 2)
.frame(width: 200, height: 200)
.offset(y: 160)
.clipped()
.offset(y: -160)
Text(date).font(.system(size: 70.0))
.offset(y: 20)
}
Spacer()
Spacer()
}.padding()
}
}
and I call this in my code using:
ScrollView(showsIndicators: false) {
VStack {
Spacer()
ZStack {
if showseconddate == false {
Calendar(date: "18").animation(.easeInOut(duration: 1.0))
.transition(.opacity)
}
if showseconddate == true {
Calendar(date: "19").animation(.easeInOut(duration: 1.0))
.transition(.opacity)
}
Spacer()
}
}.onAppear {
Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { timer in
withAnimation(Animation.linear(duration: 0.5)) {
self.showseconddate.toggle()
self.showfirstdate.toggle() }
timer.invalidate()
}
}
}
This all works as intended, but I'm struggling to then expand this to a case where I want to show it transitioning through multiple dates, such as 18 > 19 >20 >21 etc. Does anyone know how to expand this, or to use an alternative solution? Any solution must fade out the old date, then fade in the new date. Many thanks!

Answer 1

Here's a relatively compact solution. Instead of relying on Bool values, it cycles through an array:
struct ContentView: View {
private var dates = ["18","19","20","21","22"]
#State private var dateIndex = 0
private let timer = Timer.publish(every: 1.0, on: .main, in: .common).autoconnect()
var body: some View{
ScrollView(showsIndicators: false) {
VStack {
Spacer()
ZStack {
Calendar(date: dates[dateIndex])
.transition(.opacity)
.id("date-\(dateIndex)")
Spacer()
}
}.onReceive(timer) { _ in
var newIndex = dateIndex + 1
if newIndex == dates.count { newIndex = 0 }
withAnimation(.easeInOut(duration: 0.5)) {
dateIndex = newIndex
}
}
}
}
}

Answer 2

I had reworked your code to get the animations running, I felt it was a bit annoying to watch the entire calendar flash, so I reworked it into a CalendarPage (I renamed Calendar to CalendarPage because Calendar is a Type in Swift) and CalendarView that takes the date and overlays it on the page.
CalendarPage is your Calendar with the date var and Text() removed:
struct CalendarPage: View {
var body: some View {
VStack {
Spacer()
ZStack {
RoundedRectangle(cornerRadius: 20)
.stroke(Color.black, lineWidth: 2)
.frame(width: 200, height: 200)
RoundedRectangle(cornerRadius: 20)
.fill(Color.red)
.frame(width: 200, height: 200)
.offset(y: 160)
.clipped()
.offset(y: -160)
RoundedRectangle(cornerRadius: 20)
.stroke(Color.black, lineWidth: 2)
.frame(width: 200, height: 200)
.offset(y: 160)
.clipped()
.offset(y: -160)
}
Spacer()
Spacer()
}.padding()
}
}
CalendarView uses the timer to increment your dates until you reach the endDate, and it only effects the opacity of the date itself, not the whole calendar:
struct CalendarView: View {
#State var date: Int = 0
#State var animate = false
#State var calendarSize: CGFloat = 20
let endDate = 31
// This keeps the font size consistent regardless of the size of the calendar
var fontSize: CGFloat {
calendarSize * 0.45
}
private let timer = Timer.publish(every: 1.0, on: .main, in: .common).autoconnect()
var body: some View {
CalendarPage(date: date.description)
.overlay(alignment: .bottom) {
VStack {
Text(date.description)
.font(.system(size: fontSize))
.opacity(animate ? 1 : 0)
}
.frame(height: calendarSize * 0.8)
}
.frame(width: 200, height: 200)
.readSize(onChange: { size in
calendarSize = min(size.width, size.height)
})
.onReceive(timer) { _ in
date += 1
withAnimation(.linear(duration: 0.3)) {
animate = true
}
DispatchQueue.main.asyncAfter(deadline: .now() + 0.75) {
if date != endDate {
withAnimation(.linear(duration: 0.2)) {
animate = false
}
} else {
timer.upstream.connect().cancel()
}
}
}
}
}
I also used a preference key to compute the height of the CalendarPage (though I could have hard coded it) using this View extension from FiveStars blog
extension View {
func readSize(onChange: #escaping (CGSize) -> Void) -> some View {
background(
GeometryReader { geometryProxy in
Color.clear
.preference(key: SizePreferenceKey.self, value: geometryProxy.size)
}
)
.onPreferenceChange(SizePreferenceKey.self, perform: onChange)
}
}
fileprivate struct SizePreferenceKey: PreferenceKey {
static var defaultValue: CGSize = .zero
static func reduce(value: inout CGSize, nextValue: () -> CGSize) {}
}