Swiftui Custom View Repeat Forever Animation Show as Unexpected

SwiftUI Custom View repeat forever animation show as unexpected

This looks like a bug of NavigationView: without it animation works totally fine. And it wan't fixed in iOS15.

Working solution is waiting one layout cycle using DispatchQueue.main.async before string animation:

struct LoadingView: View {
    @State private var isLoading = false
    var body: some View {
        Circle()
            .trim(from: 0, to: 0.8)
            .stroke(Color.red, lineWidth: 5)
            .frame(width: 30, height: 30)
            .rotationEffect(Angle(degrees: isLoading ? 360 : 0))
            .onAppear {
                DispatchQueue.main.async {
                    withAnimation(.linear(duration: 1).repeatForever(autoreverses: false)) {
                        self.isLoading.toggle()
                    }
                }
            }
    }
}

SwiftUI: Broken explicit animations in NavigationView?

Here is fixed part (another my answer with explanations is here).

Tested with Xcode 12 / iOS 14.

struct EscapingAnimationTest_Inner: View {
    @State var degrees: CGFloat = 0
    
    var body: some View {
        Circle()
            .trim(from: 0.0, to: 0.3)
            .stroke(Color.red, lineWidth: 5)
            .rotationEffect(Angle(degrees: Double(degrees)))
            .animation(Animation.linear(duration: 1).repeatForever(autoreverses: false), value: degrees)
            .onAppear() {
                DispatchQueue.main.async {   // << here !!
                    degrees = 360
                }
            }
    }
}

Update: the same will be using withAnimation

.onAppear() {
    DispatchQueue.main.async {
        withAnimation(Animation.linear(duration: 1).repeatForever(autoreverses: false)) {
           degrees = 360
        }
    }

}

SwiftUI: Animation Inside NavigationView

The onAppear is called too early when view frame is zero being in NavigationView, so animation is applied to change from zero to value.

Here is valid workaround. Tested with Xcode 12.4 / iOS 14.4

var body: some View {
    ZStack() {
        Color.clear
        Rectangle()
            .frame(width: animate ? finalRect.width: currentRect.width, height: animate ? finalRect.height: currentRect.height, alignment: .center)
            .animation(animation, value: animate)
            .onAppear {
                DispatchQueue.main.async {   
                   // << postpone till end of views construction !!
                    animate = true
                }
            }
    }
}

Note: almost any why question can be answered only by Apple... maybe it is a bug, maybe an implementation specifics.

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