Add FB13705157

FB13705157/README.md

@@ -0,0 +1,34 @@
+# Sheet background flashes when changing detents
+
+## Basic Information
+### Which platform is most relevant for your report?
+iOS
+
+### Which technology does your report involve?
+SwiftUI
+
+### What type of feedback are you reporting?
+Incorrect/Unexpected Behavior
+
+### What build does the issue occur on?
+iOS 17.4 Seed 3 (21E5200d)
+
+### Where does the issue occur?
+On device
+
+## Description
+- Run the given code.
+- Drag the sheet up and down.
+- Notice that the background of the sheet flashes, when the background is partially transparent.
+- I would expect the background of the sheet not to flash.
+- Moving the `SheetView` into `ContentView` seems to reduce the _chances_ of it happening, but doesn't solve the problem.
+- Can use [SwiftUIIntrospect](https://github.com/siteline/swiftui-introspect) as a workaround.
+
+## Evidence
+### GIFs
+| Demo | Workaround |
+|:-:|:-:|
+| ![Demo GIF](demo.gif) | ![Workaround GIF](workaround.gif) |
+
+### Code
+TODO

FB13705157/demo.swift

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+import SwiftUI
+
+struct ContentView: View {
+    @State private var presented = true
+
+    var body: some View {
+        Button("Present") {
+            presented = true
+        }
+        .sheet(isPresented: $presented) {
+            SheetView()
+        }
+        .frame(maxWidth: .infinity, maxHeight: .infinity)
+        .background(Color.red)
+    }
+}
+
+struct SheetView: View {
+    @State private var detent: PresentationDetent = .medium
+
+    var body: some View {
+        Text("Sheet")
+            .presentationBackground(.regularMaterial)
+            .presentationDetents([.medium, .large], selection: $detent)
+    }
+}
+
+#Preview {
+    ContentView()
+}

FB13705157/workaround.swift

@@ -0,0 +1,34 @@
+import SwiftUI
+import SwiftUIIntrospect
+
+struct ContentView: View {
+    @State private var presented = true
+
+    var body: some View {
+        Button("Present") {
+            presented = true
+        }
+        .sheet(isPresented: $presented) {
+            SheetView()
+        }
+        .frame(maxWidth: .infinity, maxHeight: .infinity)
+        .background(Color.red)
+    }
+}
+
+struct SheetView: View {
+    @State private var detent: PresentationDetent = .medium
+
+    var body: some View {
+        Text("Sheet")
+            .presentationBackground(.regularMaterial)
+            .presentationDetents([.medium, .large], selection: $detent)
+            .introspect(.sheet, on: .iOS(.v17)) { sheet in
+                sheet.presentedViewController.view.backgroundColor = .clear
+            }
+    }
+}
+
+#Preview {
+    ContentView()
+}

README.md

@@ -5,6 +5,7 @@ These are the feedbacks I'm filing to Apple, to document bugs I come across. The
 
 ## Feedbacks
 - [FB13705098](FB13705098): Sheet background doesn't reach bottom when programmatically changing detent
+- [FB13705157](FB13705157): Sheet background flashes when changing detents
 
 ## Contributing
 Since this is a list of my feedbacks, please don't add entirely new feedbacks. However, if you have found a workaround not already mentioned, please create an issue with your working code. If the workaround makes use of external packages such as [SwiftUIIntrospect](https://github.com/siteline/swiftui-introspect), make that clear.