Attach default controller to sheet if not explicitly specified

package/lib/smooth_sheets.dart

@@ -1,6 +1,6 @@
 /// Comprehensive bottom sheet library supporting imperative and declarative
 /// navigation APIs, nested navigation, persistent and modal styles (including
-/// the iOS flavor),  and more.
+/// the iOS flavor), and more.
 library smooth_sheets;
 
 export 'src/draggable/draggable_sheet.dart';
@@ -12,7 +12,8 @@ export 'src/foundation/keyboard_dismissible.dart';
 export 'src/foundation/notifications.dart';
 export 'src/foundation/physics.dart';
 export 'src/foundation/sheet_content_scaffold.dart';
-export 'src/foundation/sheet_controller.dart' hide SheetControllerScope;
+export 'src/foundation/sheet_controller.dart'
+    hide ImplicitSheetControllerScope, SheetControllerScope;
 export 'src/foundation/sheet_extent.dart';
 export 'src/foundation/theme.dart';
 export 'src/modal/cupertino.dart';

package/lib/src/draggable/draggable_sheet.dart

@@ -71,18 +71,23 @@ class DraggableSheet extends StatelessWidget {
     final keyboardDismissBehavior =
         this.keyboardDismissBehavior ?? theme?.keyboardDismissBehavior;
 
-    Widget result = SheetContainer(
+    Widget result = ImplicitSheetControllerScope(
       controller: controller,
-      config: DraggableSheetExtentConfig(
-        initialExtent: initialExtent,
-        minExtent: minExtent,
-        maxExtent: maxExtent,
-        physics: physics,
-      ),
-      child: SheetDraggable(
-        behavior: hitTestBehavior,
-        child: child,
-      ),
+      builder: (context, controller) {
+        return SheetContainer(
+          controller: controller,
+          config: DraggableSheetExtentConfig(
+            initialExtent: initialExtent,
+            minExtent: minExtent,
+            maxExtent: maxExtent,
+            physics: physics,
+          ),
+          child: SheetDraggable(
+            behavior: hitTestBehavior,
+            child: child,
+          ),
+        );
+      },
     );
 
     if (keyboardDismissBehavior != null) {

package/lib/src/foundation/framework.dart

@@ -1,18 +1,20 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
+import 'package:flutter/widgets.dart';
+
 import 'sheet_controller.dart';
 import 'sheet_extent.dart';
 
 class SheetContainer extends StatelessWidget {
   const SheetContainer({
     super.key,
-    this.controller,
     this.onExtentChanged,
+    required this.controller,
     required this.config,
     required this.child,
   });
 
-  final SheetController? controller;
+  final SheetController controller;
   final ValueChanged<SheetExtent?>? onExtentChanged;
   final SheetExtentConfig config;
   final Widget child;
@@ -21,7 +23,7 @@ class SheetContainer extends StatelessWidget {
   Widget build(BuildContext context) {
     return SheetExtentScope(
       config: config,
-      controller: controller ?? SheetControllerScope.maybeOf(context),
+      controller: controller,
       onExtentChanged: onExtentChanged,
       child: Builder(
         builder: (context) {

package/lib/src/foundation/sheet_controller.dart

@@ -2,6 +2,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter/widgets.dart';
 import 'package:meta/meta.dart';
+
 import 'sheet_extent.dart';
 
 class SheetController extends ChangeNotifier
@@ -113,6 +114,40 @@ class SheetControllerScope extends InheritedWidget {
   }
 }
 
+/// A widget that ensures that a [SheetController] is available in the subtree.
+///
+/// The [builder] callback will be called with the [controller] if it is
+/// explicitly provided and is not null, or a [SheetController] that is hosted
+/// in the nearest ancestor [SheetControllerScope]. If neither is found, a newly
+/// created [SheetController] hosted in a [DefaultSheetController] will be
+/// used as a fallback.
+@internal
+class ImplicitSheetControllerScope extends StatelessWidget {
+  const ImplicitSheetControllerScope({
+    super.key,
+    this.controller,
+    required this.builder,
+  });
+
+  final SheetController? controller;
+  final Widget Function(BuildContext, SheetController) builder;
+
+  @override
+  Widget build(BuildContext context) {
+    return switch (controller ?? DefaultSheetController.maybeOf(context)) {
+      final controller? => builder(context, controller),
+      null => DefaultSheetController(
+          child: Builder(
+            builder: (context) {
+              final controller = DefaultSheetController.of(context);
+              return builder(context, controller);
+            },
+          ),
+        ),
+    };
+  }
+}
+
 class DefaultSheetController extends StatefulWidget {
   const DefaultSheetController({
     super.key,

package/lib/src/navigation/navigation_sheet.dart

@@ -101,13 +101,18 @@ class NavigationSheetState extends State<NavigationSheet>
     final keyboardDismissBehavior =
         widget.keyboardDismissBehavior ?? theme?.keyboardDismissBehavior;
 
-    Widget result = SheetContainer(
-      config: const _NavigationSheetExtentConfig(),
+    Widget result = ImplicitSheetControllerScope(
       controller: widget.controller,
-      onExtentChanged: (extent) {
-        _extent = extent as _NavigationSheetExtent?;
+      builder: (context, controller) {
+        return SheetContainer(
+          config: const _NavigationSheetExtentConfig(),
+          controller: widget.controller ?? DefaultSheetController.of(context),
+          onExtentChanged: (extent) {
+            _extent = extent as _NavigationSheetExtent?;
+          },
+          child: widget.child,
+        );
       },
-      child: widget.child,
     );
 
     if (keyboardDismissBehavior != null) {

package/lib/src/scrollable/scrollable_sheet.dart

@@ -49,15 +49,20 @@ class ScrollableSheet extends StatelessWidget {
     final keyboardDismissBehavior =
         this.keyboardDismissBehavior ?? theme?.keyboardDismissBehavior;
 
-    Widget result = SheetContainer(
+    Widget result = ImplicitSheetControllerScope(
       controller: controller,
-      config: ScrollableSheetExtentConfig(
-        initialExtent: initialExtent,
-        minExtent: minExtent,
-        maxExtent: maxExtent,
-        physics: physics,
-      ),
-      child: PrimarySheetContentScrollController(child: child),
+      builder: (context, controller) {
+        return SheetContainer(
+          controller: controller,
+          config: ScrollableSheetExtentConfig(
+            initialExtent: initialExtent,
+            minExtent: minExtent,
+            maxExtent: maxExtent,
+            physics: physics,
+          ),
+          child: PrimarySheetContentScrollController(child: child),
+        );
+      },
     );
 
     if (keyboardDismissBehavior != null) {