Add isDismissible configuration for showModalBottomSheet (#42404)

* Allow showModalBottomSheet to present bottom sheet that is not dismissible by tapping on the scrim

* Add guards, improve styling and tests for BottomSheet

packages/flutter/lib/src/material/bottom_sheet.dart

@@ -343,9 +343,11 @@ class _ModalBottomSheetRoute<T> extends PopupRoute<T> {
     this.elevation,
     this.shape,
     this.clipBehavior,
+    this.isDismissible = true,
     @required this.isScrollControlled,
     RouteSettings settings,
   }) : assert(isScrollControlled != null),
+       assert(isDismissible != null),
        super(settings: settings);
 
   final WidgetBuilder builder;
@@ -355,12 +357,13 @@ class _ModalBottomSheetRoute<T> extends PopupRoute<T> {
   final double elevation;
   final ShapeBorder shape;
   final Clip clipBehavior;
+  final bool isDismissible;
 
   @override
   Duration get transitionDuration => _bottomSheetDuration;
 
   @override
-  bool get barrierDismissible => true;
+  bool get barrierDismissible => isDismissible;
 
   @override
   final String barrierLabel;
@@ -428,6 +431,9 @@ class _ModalBottomSheetRoute<T> extends PopupRoute<T> {
 /// that a modal [BottomSheet] needs to be displayed above all other content
 /// but the caller is inside another [Navigator].
 ///
+/// The [isDismissible] parameter specifies whether the bottom sheet will be
+/// dismissed when user taps on the scrim.
+///
 /// The optional [backgroundColor], [elevation], [shape], and [clipBehavior]
 /// parameters can be passed in to customize the appearance and behavior of
 /// modal bottom sheets.
@@ -453,11 +459,13 @@ Future<T> showModalBottomSheet<T>({
   Clip clipBehavior,
   bool isScrollControlled = false,
   bool useRootNavigator = false,
+  bool isDismissible = true,
 }) {
   assert(context != null);
   assert(builder != null);
   assert(isScrollControlled != null);
   assert(useRootNavigator != null);
+  assert(isDismissible != null);
   assert(debugCheckHasMediaQuery(context));
   assert(debugCheckHasMaterialLocalizations(context));
 
@@ -470,6 +478,7 @@ Future<T> showModalBottomSheet<T>({
     elevation: elevation,
     shape: shape,
     clipBehavior: clipBehavior,
+    isDismissible: isDismissible,
   ));
 }
 

packages/flutter/test/material/bottom_sheet_test.dart

@@ -14,14 +14,16 @@ void main() {
   testWidgets('Tapping on a modal BottomSheet should not dismiss it', (WidgetTester tester) async {
     BuildContext savedContext;
 
-    await tester.pumpWidget(MaterialApp(
-      home: Builder(
-        builder: (BuildContext context) {
-          savedContext = context;
-          return Container();
-        }
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Builder(
+          builder: (BuildContext context) {
+            savedContext = context;
+            return Container();
+          },
+        ),
       ),
-    ));
+    );
 
     await tester.pump();
     expect(find.text('BottomSheet'), findsNothing);
@@ -45,15 +47,15 @@ void main() {
     expect(showBottomSheetThenCalled, isFalse);
   });
 
-  testWidgets('Tapping outside a modal BottomSheet should dismiss it', (WidgetTester tester) async {
+  testWidgets('Tapping outside a modal BottomSheet should dismiss it by default', (WidgetTester tester) async {
     BuildContext savedContext;
 
     await tester.pumpWidget(MaterialApp(
       home: Builder(
-          builder: (BuildContext context) {
-            savedContext = context;
-            return Container();
-          }
+        builder: (BuildContext context) {
+          savedContext = context;
+          return Container();
+        },
       ),
     ));
 
@@ -72,15 +74,85 @@ void main() {
     expect(find.text('BottomSheet'), findsOneWidget);
     expect(showBottomSheetThenCalled, isFalse);
 
-    // Tap above the bottom sheet to dismiss it
+    // Tap above the bottom sheet to dismiss it.
     await tester.tapAt(const Offset(20.0, 20.0));
-    await tester.pump(); // bottom sheet dismiss animation starts
+    await tester.pumpAndSettle(); // Bottom sheet dismiss animation.
     expect(showBottomSheetThenCalled, isTrue);
-    await tester.pump(const Duration(seconds: 1)); // animation done
-    await tester.pump(const Duration(seconds: 1)); // rebuild frame
     expect(find.text('BottomSheet'), findsNothing);
   });
 
+  testWidgets('Tapping outside a modal BottomSheet should dismiss it when isDismissible=true', (WidgetTester tester) async {
+    BuildContext savedContext;
+
+    await tester.pumpWidget(MaterialApp(
+      home: Builder(
+        builder: (BuildContext context) {
+          savedContext = context;
+          return Container();
+        },
+      ),
+    ));
+
+    await tester.pump();
+    expect(find.text('BottomSheet'), findsNothing);
+
+    bool showBottomSheetThenCalled = false;
+    showModalBottomSheet<void>(
+      context: savedContext,
+      builder: (BuildContext context) => const Text('BottomSheet'),
+      isDismissible: true,
+    ).then<void>((void value) {
+      showBottomSheetThenCalled = true;
+    });
+
+    await tester.pumpAndSettle();
+    expect(find.text('BottomSheet'), findsOneWidget);
+    expect(showBottomSheetThenCalled, isFalse);
+
+    // Tap above the bottom sheet to dismiss it.
+    await tester.tapAt(const Offset(20.0, 20.0));
+    await tester.pumpAndSettle(); // Bottom sheet dismiss animation.
+    expect(showBottomSheetThenCalled, isTrue);
+    expect(find.text('BottomSheet'), findsNothing);
+  });
+
+  testWidgets('Tapping outside a modal BottomSheet should not dismiss it when isDismissible=false', (WidgetTester tester) async {
+    BuildContext savedContext;
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Builder(
+          builder: (BuildContext context) {
+            savedContext = context;
+            return Container();
+          },
+        ),
+      ),
+    );
+
+    await tester.pump();
+    expect(find.text('BottomSheet'), findsNothing);
+
+    bool showBottomSheetThenCalled = false;
+    showModalBottomSheet<void>(
+      context: savedContext,
+      builder: (BuildContext context) => const Text('BottomSheet'),
+      isDismissible: false,
+    ).then<void>((void value) {
+      showBottomSheetThenCalled = true;
+    });
+
+    await tester.pumpAndSettle();
+    expect(find.text('BottomSheet'), findsOneWidget);
+    expect(showBottomSheetThenCalled, isFalse);
+
+    // Tap above the bottom sheet, attempting to dismiss it.
+    await tester.tapAt(const Offset(20.0, 20.0));
+    await tester.pumpAndSettle(); // Bottom sheet should not dismiss.
+    expect(showBottomSheetThenCalled, isFalse);
+    expect(find.text('BottomSheet'), findsOneWidget);
+  });
+
   testWidgets('Verify that a downwards fling dismisses a persistent BottomSheet', (WidgetTester tester) async {
     final GlobalKey<ScaffoldState> scaffoldKey = GlobalKey<ScaffoldState>();
     bool showBottomSheetThenCalled = false;