How do I change the fixed size of a Lazy Grid GridItem in response to Dynamic Text size changes?

Question

The code below is using a LazyVGrid to implement layout of my controls such that everything lines up like this:

Particularly, the sliders' ends all align and the symbols are centre-aligned to each other. I have worked out how to size the GridItems for the symbol and the numeric readout such that they are the 'right size' for their contents — something neither flexible nor adaptive GridItems will do — while accounting for Dynamic Type.

In testing, this works really well so long as the user does not change their Dynamic Type size once the app is active. If that is done, the type (and symbols) will adapt as they should, but the GridItem size remains fixed at its initial value. This causes the numbers to wrap at the decimal point.

Is there a way to have the GridItem resize in response to Dynamic Type changes, or is there a better way to do this layout?

import SwiftUI

struct ProtoGrid: View {
   let gridItems = [
      GridItem(.fixed(UIImage(systemName: "ruler", withConfiguration: UIImage.SymbolConfiguration(textStyle: .body, scale: .large))!.size.width)),
      GridItem(.flexible(minimum: 40, maximum: .infinity)),
      GridItem(.fixed(("00.00" as NSString).size(withAttributes: [NSAttributedString.Key.font: UIFont.preferredFont(forTextStyle: .body)]).width + 4), alignment: .trailing)
   ]
   @State var index1 = 5.0
   @State var index2 = 5.0
   @State var index3 = 5.0
   var body: some View {
      VStack {
         Rectangle()
            .fill(Color.red)
         LazyVGrid(columns: gridItems, spacing: 12) {
            Image(systemName: "person").imageScale(.large)
            Slider(value: $index1, in: 0...10)
            Text("\(String(format: "%.2f", index1))").font(Font.system(.body).monospacedDigit())
            Image(systemName: "megaphone").imageScale(.large)
            Slider(value: $index2, in: 0...10)
            Text("\(String(format: "%.2f", index2))").font(Font.system(.body).monospacedDigit())
            Image(systemName: "ruler").imageScale(.large)
            Slider(value: $index3, in: 0...10)
            Text("\(String(format: "%.2f", index3))").font(Font.system(.body).monospacedDigit())
         }
         .padding()
      }
   }
}

struct ProtoGrid_Previews: PreviewProvider {
    static var previews: some View {
        ProtoGrid()
         .previewDevice("iPhone 11 Pro")
    }
}
111

Answer 1

It seems clear the purpose of your try to use grid here, to have aligned sliders due to different image sizes, but grid configuration is constant, ie you did it once. And it is pretty hardcoded, actually, so does not appropriate for dynamic text case.

I would propose alternate approach - just use regular HStack, which fits content dynamically, and some custom dynamic alignment for content.

Tested with Xcode 12 / iOS 14

struct ProtoGrid: View {

    @State var index1 = 5.0
    @State var index2 = 5.0
    @State var index3 = 5.0

    @State private var imageWidth = CGFloat.zero

    var body: some View {
        VStack {
            Rectangle()
                .fill(Color.red)
            HStack(spacing: 12) {
                Image(systemName: "person").imageScale(.large)
                    .alignedView(width: $imageWidth)
                Slider(value: $index1, in: 0...10)
                Text("\(String(format: "%.2f", index1))").font(Font.system(.body).monospacedDigit())
            }
            HStack(spacing: 12) {
                Image(systemName: "megaphone").imageScale(.large)
                    .alignedView(width: $imageWidth)
                Slider(value: $index2, in: 0...10)
                Text("\(String(format: "%.2f", index2))").font(Font.system(.body).monospacedDigit())
            }
             HStack(spacing: 12) {
                Image(systemName: "ruler").imageScale(.large)
                    .alignedView(width: $imageWidth)
                Slider(value: $index3, in: 0...10)
                Text("\(String(format: "%.2f", index3))").font(Font.system(.body).monospacedDigit())
            }
        }
        .padding()
    }
}

extension View {
    func alignedView(width: Binding<CGFloat>) -> some View {
        self.modifier(AlignedWidthView(width: width))
    }
}

// creates a view which uses max width of calculated intrinsic
// content or shared from external width, updating external
// bound variable if own width is bigger.
struct AlignedWidthView: ViewModifier {
    @Binding var width: CGFloat

    func body(content: Content) -> some View {
        content
            .background(GeometryReader {
                Color.clear
                    .preference(key: ViewWidthKey.self, value: $0.frame(in: .local).size.width)
            })
            .onPreferenceChange(ViewWidthKey.self) {
                if $0 > self.width {
                    self.width = $0
                }
            }
            .frame(width: width)
    }
}

struct ViewWidthKey: PreferenceKey {
    typealias Value = CGFloat
    static var defaultValue = CGFloat.zero
    static func reduce(value: inout Value, nextValue: () -> Value) {
        value += nextValue()
    }
}