SwiftUI: how to animate transition between two Images using a delay?

Question

I have two images, ImageA and ImageB, and my goal is to animate a transition between them in the following manner:

ImageA is loaded
Pause for 1 second
ImageA transitions to ImageB, with a duration of 1.5 seconds

With regular Swift, it would be using an UIView.animate closure with an animation duration and a pause.

Here is my attempt with SwiftUI, which is not showing a smooth transition, but a hard image change instead:

VStack(alignment: .leading, spacing: 0) {
            Image(images.randomElement()!)
                    .resizable()
                    .scaledToFill()
                    .onAppear {
                        DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) {
                        withAnimation() { //added
                            self.shouldTransition.toggle()
                        }
                    }
                    
            if shouldTransition {
                Image(images.randomElement()!)
                        .resizable()
                        .animation(.easeInOut(duration: 1.5))
                        .scaledToFill()
            }
            
        }

What is missing in my implementation to animate the image transition?

Edit: the entire codebase can be found here: TestWidget Github

Asperi · Accepted Answer · 2020-10-12 13:53:35Z

3

You don't specify which kind of transition do you want, by default SwiftUI uses opacity...

Try the following

VStack(alignment: .leading, spacing: 0) {
    if !shouldTransition {
        Image(images.randomElement()!)
            .resizable()
            .scaledToFill()
            .onAppear {
                DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) {
                    self.shouldTransition.toggle()
                }
            }
            //.transition(.move(edge: .top))      // uncomment to modify transition
    }

    if shouldTransition {
        Image(images.randomElement()!)
            .resizable()
            .scaledToFill()
            //.transition(.move(edge: .top))      // uncomment to modify transition
    }
    
}.animation(.easeInOut(duration: 1.5), value: shouldTransition)

answered Oct 12, 2020 at 13:53

Asperi

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4 Comments

daspianist Over a year ago

Thanks for sharing this. This definitely seemed promising but unfortunately the same result: no animation between image changes (I uncommented the two .transition()s per comments in the code). I have uploaded the entire codebase and updated the question body

Asperi Over a year ago

I missed that this is widget... it will not work in widget - it is statically rendered.

daspianist Over a year ago

I see - that explains it. Thanks for sharing your insight

Niklas Over a year ago

Amazing solution @Asperi, highly appreciated!

Gabriel Balta · Accepted Answer · 2020-10-12 11:53:31Z

1

You have to add withAnimation() { ... } wrapper around observed changes, which you want to be animated.

Change your code to

DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) {
                                withAnimation(){
                                self.shouldTransition.toggle()
                                }
                            }

answered Oct 12, 2020 at 11:53

Gabriel Balta

667 bronze badges

1 Comment

daspianist Over a year ago

Thanks for suggesting this. I added withAnimation() but the image transition still does not show an animation but a sudden image change. I also updated the code in the body of the question.

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