Reload SwiftUI view from within it

Question

I have some text inside a View and I want this text to change it's position on timer. I have the following:

struct AlphabetView: View {
    @State var timer: Publishers.Autoconnect<Timer.TimerPublisher> = Timer.publish(every: 0.1, on: .main, in: .common).autoconnect()
    @State var refreshMe: Bool = false // this is a hack to refresh the view
    
    var relativePositionX: CGFloat {
        get { return CGFloat(Float.random(in: 0...1)) }
    }
    
    var relativePositionY: CGFloat {
        get { return CGFloat(Float.random(in: 0...1)) }
    }
    
    var body: some View {
        GeometryReader { geometry in
            Text("Hello World!")
                .position(x: geometry.size.width * self.relativePositionX, y: geometry.size.height * self.relativePositionY)
                .onReceive(timer) { _ in
                    // a hack to refresh the view
                    self.refreshMe = !self.refreshMe
                }
        }
    }
}

I suppose that the View should be reloaded every time self.refreshMe changes, because it is @State. But what I see is that the text position changes only when the parent view of the view in question is reloaded. What am I doing wrong (except hacking around)? Is there a better way to do this?

Your hack isn't working because your view doesn't actually use refreshMe. Adding something like .foregroundColor(self.refreshMe ? .black : .black) is enough to get SwiftUI to trigger the update. — vacawama
– vacawama, Commented Oct 11, 2020 at 18:47
BTW, CGFloat also has .random(in:), so var relativePositionX: CGFloat { .random(in: 0...1) } is sufficient. — vacawama
– vacawama, Commented Oct 11, 2020 at 19:44

Asperi · Accepted Answer · 2020-10-11 18:29:51Z

2

Instead of hack just update position directly.

Here is corrected variant. Tested with Xcode 12 / iOS 14.

struct AlphabetView: View {
    let timer: Publishers.Autoconnect<Timer.TimerPublisher> = Timer.publish(every: 0.1, on: .main, in: .common).autoconnect()

    @State var point: CGPoint = .zero
    
    var relativePositionX: CGFloat {
        get { return CGFloat(Float.random(in: 0...1)) }
    }
    
    var relativePositionY: CGFloat {
        get { return CGFloat(Float.random(in: 0...1)) }
    }
    
    var body: some View {
        GeometryReader { geometry in
            Text("Hello World!")
                .position(self.point)
                .onReceive(timer) { _ in
                    self.point = CGPoint(x: geometry.size.width * self.relativePositionX, y: geometry.size.height * self.relativePositionY)
                }
        }
    }
}

answered Oct 11, 2020 at 18:29

Asperi

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1 Comment

Roman Reimche Over a year ago

This solves the problem completely, thank you very much.

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