Fetching view frame, including on List, using GeometryReader

ContentView.swift

struct ListCellView: View {
    struct Selection: Equatable {
        let label: String
        let frame: CGRect
    }

    @State private var cellFrame: CGRect = .zero
    
    let label: String
    let action: (Selection) async -> Void
    
    var body: some View {
        VStack {
            Text("Cell: \(label)")
                .frame(maxWidth: .infinity, alignment: .leading)
            Text("Origin: \(cellFrame.origin.x, specifier: "%.0f") x \(cellFrame.origin.y, specifier: "%.0f")")
                .font(.footnote)
                .frame(maxWidth: .infinity, alignment: .leading)
            Text("Size: \(cellFrame.size.width, specifier: "%.0f") x \(cellFrame.size.height, specifier: "%.0f")")
                .font(.footnote)
                .frame(maxWidth: .infinity, alignment: .leading)
        }
        .padding()
        .background(.separator)
        .fetchFrame { cellFrame = $0 }
        .onTapGesture { Task {
            await action(Selection(label: label, frame: cellFrame))
        }}
    }
}

struct ContentView: View {
    @State private var selection: ListCellView.Selection? = nil
    @State private var fullViewFrame: CGRect = .zero
    
    @ViewBuilder
    var content: some View {
        List(0..<100) { position in
            ListCellView(label: "\(position)") { selection in
                self.selection = selection
            }
        }
    }
    
    @ViewBuilder
    func text(for selection: ListCellView.Selection) -> some View {
        //Text being configured as a view that is independent from the placement
        Text(selection.label)
            .frame(maxWidth: .infinity, maxHeight: .infinity)
            .font(.title)
            .background(.black)
            .foregroundStyle(.white)
    }
    
    @ViewBuilder
    var animationRectangle: some View {
        if let selection  {
            text(for: selection)
                //Position the view
                .frame(
                    width: selection.frame.width,
                    height: selection.frame.height
                )
                .position(
                    x: selection.frame.midX,
                    y: selection.frame.midY
                )
                //Animate change
                .animation(.easeInOut, value: selection)
                //Dismiss
                .onTapGesture { self.selection = nil }
        }
    }
    
    var body: some View {
        content
            .safeAreaPadding(.top)
            .padding(.top)
            .overlay { animationRectangle }
            .ignoresSafeArea()
            .fetchFrame { fullViewFrame = $0 }
    }
}

#Preview {
    ContentView()
}

GeometryReaderOverlay.swift

extension View {
    /// This method uses GeometryReader as an overlay to compute the view frame without interfering in the actual frame calculation.
    /// Allowing, for example, the measure of Views of a List.
    ///
    /// - Parameter coordinateSpace: The desired coordinate space that the frame will be calculated
    /// - Parameter update: Method that will receive the calculated frame
    /// - Returns: View with an overlay
    func fetchFrame(
        in coordinateSpace: CoordinateSpace = .global,
        update: @escaping (CGRect) async -> Void
    ) -> some View {
        //GeometryReader used as overlay to avoid
        //breaking inner view frame calculation
        overlay { GeometryReader { proxy in
            let proxyFrame = proxy.frame(in: coordinateSpace)
            
            //Update as a task to avoid clogging the main thread
            let _ = Task { await update(proxyFrame) }
            
            //Random view to ocupy the full space and allow measure
            Rectangle().foregroundStyle(.clear)
        }}
    }
}

Here is a demonstration of the ContentView.swift above in a project:

Screen.Recording.2024-01-15.at.17.14.54.mov