How do I pass a View into a struct while getting its height also?

Question

I'm trying to make a View that will put a Blur() at the bottom of an iPhone layout, respecting safeareas and that I can easily reuse.

Something like this:

import SwiftUI

struct SafeBottomBlurContainer: View {
    @Environment(\.colorScheme) var colorScheme
    var body: some View {
        GeometryReader { geometry in
            VStack {
                Spacer()
                ZStack {
                    Blur(style:  self.colorScheme == .dark ? .systemThinMaterialDark : .systemThinMaterialLight)
                        .frame(
                            width: geometry.size.width,
                            height: geometry.safeAreaInsets.bottom + 50
                        )
                        Holder()
                            .padding(.bottom, geometry.safeAreaInsets.bottom)
                }
            }
            .edgesIgnoringSafeArea(.bottom)
        }
    }
}

struct Holder: View {
    var body: some View {
        Rectangle().opacity(0.5)
            .frame(height: 50)
    }
}


struct SafeBottomBlurContainer_Previews: PreviewProvider {
    
    static var previews: some View {
        SafeBottomBlurContainer()
    }
}

Here is the ~~blue~~ blur extension, by the way:

import SwiftUI

struct Blur: UIViewRepresentable {
    var style: UIBlurEffect.Style = .systemMaterial
    func makeUIView(context: Context) -> UIVisualEffectView {
        return UIVisualEffectView(effect: UIBlurEffect(style: style))
    }
    func updateUIView(_ uiView: UIVisualEffectView, context: Context) {
        uiView.effect = UIBlurEffect(style: style)
    }
}

Now, what I'd like to do is somehow pass in Holder() so that I can adjust the height of the Blur (which here is + 50). I feel like I should be using AnyView in some manner, but can't figure it out. That might be me on the wrong track.

Here is how I'd like to use it in a ContentView() example:

import SwiftUI

struct ContentView: View {
    var body: some View {
        
        ZStack {
            Color.pink.edgesIgnoringSafeArea(.all)
            SafeBottomBlurContainer(containedView: MyCustomViewWithWhateverHeight)
        }
    }
}

Answer 1

Here is possible approach, that gives possibility to use container like

struct ContentView: View {
    var body: some View {
        
        ZStack {
            Color.pink.edgesIgnoringSafeArea(.all)

            // holder is not needed, because you can pass any view directly
            SafeBottomBlurContainer(containedView: Text("Demo"))
        }
    }
}

and generic blur container

struct SafeBottomBlurContainer<V: View>: View {
    @Environment(\.colorScheme) var colorScheme

    var containedView: V
    var body: some View {
        GeometryReader { geometry in
            VStack {
                Spacer()
                ZStack {
                    Blur(style:  self.colorScheme == .dark ? .systemThinMaterialDark : .systemThinMaterialLight)
                        .frame(
                            width: geometry.size.width,
                            height: geometry.safeAreaInsets.bottom + 50
                        )
                        containedView
                            .padding(.bottom, geometry.safeAreaInsets.bottom)
                }
            }
            .edgesIgnoringSafeArea(.bottom)
        }
    }
}

Answer 2

Taking the lead from @Asperi who really put me on the right track, I now have this, trying to also accmomodate whether this Blur() view should be at the top or bottom of the screen:

import SwiftUI

struct SafeEdgesBlurContainer<V: View>: View {
    @Environment(\.colorScheme) var colorScheme
    @State var containedViewSize: CGSize = .zero
    var containedView: V
    var isPlacedAtTop: Bool
    var body: some View {
        GeometryReader { geometry in
            VStack {
                if !isPlacedAtTop {
                Spacer()
                }
                ZStack {
                    Blur(style:  self.colorScheme == .dark ? .systemThinMaterialDark : .systemThinMaterialLight)
                        .frame(
                            width: geometry.size.width + geometry.safeAreaInsets.leading + geometry.safeAreaInsets.trailing,
                            height: (isPlacedAtTop ? geometry.safeAreaInsets.top : geometry.safeAreaInsets.bottom ) + containedViewSize.height
                        )
                        .edgesIgnoringSafeArea([.leading])
                    HStack {
                        ChildSizeReader(size: $containedViewSize) {
                                containedView
                        }
                        .frame(width: geometry.size.width)  // ADDED This line to keep the ContainedView centered in Landscape
                        .padding(isPlacedAtTop ? .top : .bottom, isPlacedAtTop ? geometry.safeAreaInsets.top : geometry.safeAreaInsets.bottom)
                    }
                }
                if isPlacedAtTop {
                Spacer()
                }
            }
            .edgesIgnoringSafeArea(isPlacedAtTop ? .top : .bottom)
        }
    }
}

It turns out to be not that hard to get the height of the ContainedView(). I found this solution from here: SwiftUI - Get size of child?

struct ChildSizeReader<Content: View>: View {
    @Binding var size: CGSize
    let content: () -> Content
    var body: some View {
        ZStack {
            content()
                .background(
                    GeometryReader { proxy in
                        Color.clear
                            .preference(key: SizePreferenceKey.self, value: proxy.size)
                    }
                )
        }
        .onPreferenceChange(SizePreferenceKey.self) { preferences in
            self.size = preferences
        }
    }
}

struct SizePreferenceKey: PreferenceKey {
    typealias Value = CGSize
    static var defaultValue: Value = .zero

    static func reduce(value _: inout Value, nextValue: () -> Value) {
        _ = nextValue()
    }
}

The remaining problem I see is that the ContainedView() is not being centered in landscape view. But hopefully, I can come back soon and edit in a solution for that.

EDIT: This might be that solution: .frame(width: geometry.size.width) on the HStack.