Always use system sheets on iOS 27, also when pushed

Example/ExampleCardViewController.swift

@@ -28,12 +28,6 @@ class ExampleCardViewController: TGCardViewController {
 
     navigationButtonsAreSpringLoaded = true
 
-    // Pass `-classicCards` as a launch argument to compare with the classic
-    // presentation, where the cards aren't in a system sheet.
-    if ProcessInfo.processInfo.arguments.contains("-classicCards") {
-      presentationStyle = .classic
-    }
-
     #if targetEnvironment(macCatalyst)
     mode = .sidebar
     #endif

README.md

@@ -74,7 +74,7 @@ Provides a card-based view controller for mapping applications where the card's
 
 ### System sheets on iOS 27+
 
-By default (`presentationStyle = .automatic`), on iOS 27 and later the cards are shown in a system sheet (`UISheetPresentationController`). The sheet adapts to the size classes by itself, like Maps':
+On iOS 27 and later, the cards are shown in a system sheet (`UISheetPresentationController`). The sheet adapts to the size classes by itself, like Maps':
 
 | | Presentation |
 |---|---|
@@ -84,7 +84,7 @@ By default (`presentationStyle = .automatic`), on iOS 27 and later the cards are
 | The card controller is itself presented, but not full screen | Classic |
 | iOS 26 and earlier, or built with Xcode 26 and earlier | Classic |
 
-Set `presentationStyle` to `.classic` to opt out. Check `usesSystemSheet` for what's currently in use.
+This can't be turned off: `presentationStyle` and its `.classic` option are deprecated on iOS 27, and will be removed once that's the minimum. Check `usesSystemSheet` for what's currently in use.
 
 Cards, map managers, headers, map buttons and paging work the same in both. Differences with a system sheet:
 

Sources/TGCardViewController/TGCardViewController+SystemSheet.swift

@@ -27,6 +27,10 @@ extension TGCardViewController {
 
     /// The card controller positions the cards itself, and they're dragged using
     /// its own gestures.
+    ///
+    /// Has no effect on iOS 27 and later, where cards always show in a system
+    /// sheet. On earlier versions, ``automatic`` does the same.
+    @available(iOS, deprecated: 27.0, message: "Cards always show in a system sheet on iOS 27 and later; earlier versions use the classic presentation anyway.")
     case classic
   }
 
@@ -72,7 +76,6 @@ extension TGCardViewController {
 #if compiler(>=6.4) && os(iOS) && !targetEnvironment(macCatalyst) // Xcode 27 proxy, for the sheet placement API
     guard
       #available(iOS 27.0, *),
-      presentationStyle == .automatic,
       mode == .floating
     else { return false }
 
@@ -124,35 +127,38 @@ extension TGCardViewController {
       installSystemSheet()
     } else if !wantsSheet, sheetHost != nil {
       uninstallSystemSheet(animated: topCardView == nil && isVisible)
-    } else if !wantsSheet, isAwaitingSystemSheet {
-      revealClassicCards()
     }
   }
 
-  private func revealClassicCards() {
-    guard isAwaitingSystemSheet else { return }
-    isAwaitingSystemSheet = false
-    toggleCardWrappers(hide: topCardView == nil)
-  }
-
 }
 
 // MARK: - Installing and removing the sheet
 
 extension TGCardViewController {
 
   private func installSystemSheet() {
+    // Can't present while a transition is under way, e.g., when this got
+    // pushed onto a navigation stack, as `viewDidAppear` gets called before
+    // that transition fully completes. Keep the cards hidden and try again
+    // right after it, rather than showing them the classic way.
+    if let coordinator = transitionCoordinator {
+      coordinator.animate(alongsideTransition: nil) { [weak self] _ in
+        DispatchQueue.main.async {
+          self?.updateSystemSheetPresentation()
+        }
+      }
+      return
+    }
+
     guard
       isVisible,
       view.window != nil,
       presentedViewController == nil,
-      transitionCoordinator == nil,
       let content = cardWrapperContent
     else {
       // We'll try again later, e.g., after the presented view controller got
-      // dismissed. Until then, show the cards in the classic way, as we don't
-      // know when that'll be.
-      revealClassicCards()
+      // dismissed. Until then, the cards stay hidden, as they never show the
+      // classic way when we want a sheet.
       return
     }
 
@@ -191,7 +197,6 @@ extension TGCardViewController {
 
     // 2. Configure the sheet
     sheetHost = host
-    isAwaitingSystemSheet = false
 
 #if !os(visionOS) // No detents on visionOS, where cards never use a sheet
     if let sheet = host.sheetPresentationController {

Sources/TGCardViewController/TGCardViewController.swift

@@ -155,7 +155,9 @@ open class TGCardViewController: UIViewController {
   /// uses system sheets on iOS 27+. Check ``usesSystemSheet`` for what's
   /// currently used.
   ///
-  /// - Warning: Set before `viewDidLoad` is called.
+  /// - Note: Has no effect: cards always show in a system sheet on iOS 27 and
+  ///   later, and the classic way before.
+  @available(iOS, deprecated: 27.0, message: "Cards always show in a system sheet on iOS 27 and later; earlier versions use the classic presentation anyway.")
   public var presentationStyle: PresentationStyle = .automatic
 
   // MARK: System sheet state, see `TGCardViewController+SystemSheet.swift`
@@ -183,10 +185,6 @@ open class TGCardViewController: UIViewController {
   var sheetTargetPosition: TGCardPosition?
   var isSheetDraggingEnabled = true
 
-  /// Set while the initial cards wait for the sheet, so that they don't flash up
-  /// in the classic presentation first
-  var isAwaitingSystemSheet = false
-
   /// Set while pushing or popping, which update the sheet in one go
   var isTransitioningCards = false
 
@@ -728,9 +726,7 @@ open class TGCardViewController: UIViewController {
         didAddInitialCards = true
 
         // These get pushed the classic way and move into the sheet once we've
-        // appeared. Keep them hidden until then.
-        isAwaitingSystemSheet = wantsSystemSheet
-
+        // appeared. They're hidden until then, see `toggleCardWrappers`.
         initialCards.forEach { push($0, animated: false, allowToNotify: $0 == initialCards.last, completionHandler: nil) }
       }
 
@@ -900,8 +896,9 @@ open class TGCardViewController: UIViewController {
     } else {
       sidebarBackground.alpha = 0
     }
-    // With a system sheet, the card wrapper is just an invisible placeholder
-    cardWrapperShadow.alpha = hide || usesSystemSheet || isAwaitingSystemSheet ? 0 : 1
+    // With a system sheet, the card wrapper is just an invisible placeholder,
+    // and it stays invisible while waiting for the sheet to be presented
+    cardWrapperShadow.alpha = hide || usesSystemSheet || wantsSystemSheet ? 0 : 1
 
     if !prepareOnly {
       if mode == .sidebar {