Add conditional modal sheet popping feature (#41)

Closes #18.

# New Feature
- Add `SheetDismissible`, which enables the enclosed sheet to be
dismissed by a drag-down gesture. It accepts an `onDismiss` callback,
which will be invoked when the user tries to dismiss the sheet by
dragging it down, providing an opportunity to determine if the sheet
should be dismissed.

# Changes
- Add tutorial code for `SheetDismissible`.
- Update the Safari and the AI playlist generator example to use
`SheetDismissible` to show a confirmation dialog to discard changes.

# Breaking Changes
- Remove `ModalSheetRouteMixin.enablePullToDismiss`.

.github/workflows/code_check.yaml

@@ -83,3 +83,17 @@ jobs:
           name: Test Report
           path: ${{ env.FLUTTER_TEST_REPORT }}
           reporter: flutter-json
+
+  # Final results (Used for status checks)
+  code-check:
+    if: ${{ always() }}
+    runs-on: ubuntu-latest
+    needs: [analysis, testing]
+    steps:
+      # Fails if any of the previous jobs failed.
+      - run: exit 1
+        if: >-
+          ${{
+               contains(needs.*.result, 'failure')
+            || contains(needs.*.result, 'cancelled')
+          }}

cookbook/lib/showcase/ai_playlist_generator.dart

@@ -56,12 +56,9 @@ final _sheetShellRoute = ShellRoute(
   pageBuilder: (context, state, navigator) {
     // Use ModalSheetPage to show a modal sheet.
     return ModalSheetPage(
-      child: SafeArea(
-        bottom: false,
-        child: NavigationSheet(
-          transitionObserver: sheetTransitionObserver,
-          child: _SheetShell(navigator: navigator),
-        ),
+      child: _SheetShell(
+        navigator: navigator,
+        transitionObserver: sheetTransitionObserver,
       ),
     );
   },
@@ -143,19 +140,61 @@ class _Root extends StatelessWidget {
 
 class _SheetShell extends StatelessWidget {
   const _SheetShell({
+    required this.transitionObserver,
     required this.navigator,
   });
 
+  final NavigationSheetTransitionObserver transitionObserver;
   final Widget navigator;
 
   @override
   Widget build(BuildContext context) {
-    return Material(
-      // Add circular corners to the sheet.
-      borderRadius: BorderRadius.circular(16),
-      clipBehavior: Clip.antiAlias,
-      color: Theme.of(context).colorScheme.surface,
-      child: navigator,
+    void showCancelDialog() {
+      showDialog(
+        context: context,
+        builder: (context) {
+          return AlertDialog(
+            title: const Text('Are you sure?'),
+            content:
+                const Text('Do you want to cancel the playlist generation?'),
+            actions: [
+              TextButton(
+                onPressed: () => context.go('/'),
+                child: const Text('Yes'),
+              ),
+              TextButton(
+                onPressed: () => Navigator.pop(context),
+                child: const Text('No'),
+              ),
+            ],
+          );
+        },
+      );
+    }
+
+    return SafeArea(
+      bottom: false,
+      // Wrap the sheet in a SheetDismissible to enable pull-to-dismiss action.
+      child: SheetDismissible(
+        // This callback is invoked when the user tries
+        // to dismiss the sheet by dragging it down.
+        onDismiss: () {
+          // Prompt the user to confirm if they want to dismiss the sheet.
+          showCancelDialog();
+          // Returns false to disable automatic modal sheet popping.
+          return false;
+        },
+        child: NavigationSheet(
+          transitionObserver: sheetTransitionObserver,
+          child: Material(
+            // Add circular corners to the sheet.
+            borderRadius: BorderRadius.circular(16),
+            clipBehavior: Clip.antiAlias,
+            color: Theme.of(context).colorScheme.surface,
+            child: navigator,
+          ),
+        ),
+      ),
     );
   }
 }

cookbook/lib/showcase/safari/actions.dart

@@ -6,7 +6,11 @@ void showEditActionsSheet(BuildContext context) {
   Navigator.push(
     context,
     CupertinoModalSheetRoute(
-      builder: (context) => const EditActionsSheet(),
+      builder: (context) {
+        return const SheetDismissible(
+          child: EditActionsSheet(),
+        );
+      },
     ),
   );
 }

cookbook/lib/showcase/safari/menu.dart

@@ -9,7 +9,11 @@ void showMenuSheet(BuildContext context) {
   Navigator.push(
     context,
     CupertinoModalSheetRoute(
-      builder: (context) => const MenuSheet(),
+      builder: (context) {
+        return const SheetDismissible(
+          child: MenuSheet(),
+        );
+      },
     ),
   );
 }

cookbook/lib/showcase/todo_list/todo_editor.dart

@@ -34,6 +34,36 @@ class _TodoEditorState extends State<TodoEditor> {
     super.dispose();
   }
 
+  bool onDismiss() {
+    if (!controller.canCompose.value) {
+      // Dismiss immediately if there are no unsaved changes.
+      return true;
+    }
+
+    // Show a confirmation dialog.
+    showDialog(
+      context: context,
+      builder: (context) {
+        return AlertDialog(
+          title: const Text('Discard changes?'),
+          actions: [
+            TextButton(
+              onPressed: () =>
+                  Navigator.popUntil(context, (route) => route.isFirst),
+              child: const Text('Discard'),
+            ),
+            TextButton(
+              onPressed: () => Navigator.pop(context),
+              child: const Text('Cancel'),
+            ),
+          ],
+        );
+      },
+    );
+
+    return false;
+  }
+
   @override
   Widget build(BuildContext context) {
     final titleInput = _MultiLineInput(
@@ -103,16 +133,20 @@ class _TodoEditorState extends State<TodoEditor> {
 
     return SafeArea(
       bottom: false,
-      child: ScrollableSheet(
-        keyboardDismissBehavior: const SheetKeyboardDismissBehavior.onDragDown(
-          isContentScrollAware: true,
-        ),
-        child: Container(
-          clipBehavior: Clip.antiAlias,
-          decoration: sheetShape,
-          child: SheetContentScaffold(
-            body: body,
-            bottomBar: bottomBar,
+      child: SheetDismissible(
+        onDismiss: onDismiss,
+        child: ScrollableSheet(
+          keyboardDismissBehavior:
+              const SheetKeyboardDismissBehavior.onDragDown(
+            isContentScrollAware: true,
+          ),
+          child: Container(
+            clipBehavior: Clip.antiAlias,
+            decoration: sheetShape,
+            child: SheetContentScaffold(
+              body: body,
+              bottomBar: bottomBar,
+            ),
           ),
         ),
       ),

cookbook/lib/tutorial/declarative_modal_sheet.dart

@@ -24,7 +24,11 @@ final _router = GoRouter(
             // It works with any *Sheet provided by this package!
             return ModalSheetPage(
               key: state.pageKey,
-              child: const _ExampleSheet(),
+              // Wrap your sheet with a SheetDismissible to make it
+              // dismissible by dragging it down.
+              child: const SheetDismissible(
+                child: _ExampleSheet(),
+              ),
             );
           },
         ),

cookbook/lib/tutorial/imperative_modal_sheet.dart

@@ -47,18 +47,52 @@ class _ExampleSheet extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return DraggableSheet(
-      child: Card(
-        color: Theme.of(context).colorScheme.secondaryContainer,
-        margin: EdgeInsets.zero,
-        shape: RoundedRectangleBorder(
-          borderRadius: BorderRadius.circular(20),
-        ),
-        child: const SizedBox(
-          height: 500,
-          width: double.infinity,
+    // Wrap your sheet with a SheetDismissible to make it
+    // dismissible by dragging it down.
+    return SheetDismissible(
+      // This callback is called when the user tries to dismiss the sheet
+      // by dragging it down. Return true to dismiss the sheet immediately,
+      // or false otherwise. This is useful when, for example, you want to
+      // show a confirmation dialog before dismissing the sheet.
+      onDismiss: () {
+        showConfirmDialog(context);
+        return false;
+      },
+      child: DraggableSheet(
+        child: Card(
+          color: Theme.of(context).colorScheme.secondaryContainer,
+          margin: EdgeInsets.zero,
+          shape: RoundedRectangleBorder(
+            borderRadius: BorderRadius.circular(20),
+          ),
+          child: const SizedBox(
+            height: 500,
+            width: double.infinity,
+          ),
         ),
       ),
     );
   }
+
+  void showConfirmDialog(BuildContext context) {
+    showDialog(
+      context: context,
+      builder: (context) {
+        return AlertDialog(
+          title: const Text('Are you sure?'),
+          actions: [
+            TextButton(
+              onPressed: () =>
+                  Navigator.popUntil(context, (route) => route.isFirst),
+              child: const Text('Yes'),
+            ),
+            TextButton(
+              onPressed: () => Navigator.pop(context),
+              child: const Text('No'),
+            ),
+          ],
+        );
+      },
+    );
+  }
 }

package/lib/src/modal/cupertino.dart

@@ -469,9 +469,6 @@ class _PageBasedCupertinoModalSheetRoute<T>
   @override
   bool get barrierDismissible => _page.barrierDismissible;
 
-  @override
-  bool get enablePullToDismiss => _page.enablePullToDismiss;
-
   @override
   Curve get transitionCurve => _page.transitionCurve;
 
@@ -490,7 +487,6 @@ class CupertinoModalSheetRoute<T> extends _BaseCupertinoModalSheetRoute<T> {
     super.settings,
     super.fullscreenDialog,
     required this.builder,
-    this.enablePullToDismiss = true,
     this.maintainState = true,
     this.barrierDismissible = true,
     this.barrierLabel,
@@ -510,9 +506,6 @@ class CupertinoModalSheetRoute<T> extends _BaseCupertinoModalSheetRoute<T> {
   @override
   final String? barrierLabel;
 
-  @override
-  final bool enablePullToDismiss;
-
   @override
   final bool maintainState;