Draggable Scrollable sheet (#30058)

* Draggable Scrollable sheet

packages/flutter/lib/widgets.dart

@@ -30,6 +30,7 @@ export 'src/widgets/container.dart';
 export 'src/widgets/debug.dart';
 export 'src/widgets/dismissible.dart';
 export 'src/widgets/drag_target.dart';
+export 'src/widgets/draggable_scrollable_sheet.dart';
 export 'src/widgets/editable_text.dart';
 export 'src/widgets/fade_in_image.dart';
 export 'src/widgets/focus_manager.dart';

packages/flutter/test/widgets/draggable_scrollable_sheet_test.dart

+// Copyright 2019 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  Widget _boilerplate(VoidCallback onButtonPressed) {
+    return Directionality(
+      textDirection: TextDirection.ltr,
+      child: Stack(
+        children: <Widget>[
+          FlatButton(
+            child: const Text('TapHere'),
+            onPressed: onButtonPressed,
+          ),
+          DraggableScrollableSheet(
+            maxChildSize: 1.0,
+            minChildSize: .25,
+            builder: (BuildContext context, ScrollController scrollController) {
+              return Container(
+                color: const Color(0xFFABCDEF),
+                child: ListView.builder(
+                  controller: scrollController,
+                  itemCount: 100,
+                  itemBuilder: (BuildContext context, int index) => Text('Item $index'),
+                ),
+              );
+            },
+          ),
+        ],
+      ),
+    );
+  }
+
+  for (TargetPlatform platform in TargetPlatform.values) {
+    group('$platform Scroll Physics', () {
+      debugDefaultTargetPlatformOverride = platform;
+
+      testWidgets('Can be dragged up without covering its container', (WidgetTester tester) async {
+        int taps = 0;
+        await tester.pumpWidget(_boilerplate(() => taps++));
+
+        expect(find.text('TapHere'), findsOneWidget);
+        await tester.tap(find.text('TapHere'));
+        expect(taps, 1);
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsOneWidget);
+        expect(find.text('Item 31'), findsNothing);
+
+        await tester.drag(find.text('Item 1'), const Offset(0, -200));
+        await tester.pumpAndSettle();
+        expect(find.text('TapHere'), findsOneWidget);
+        await tester.tap(find.text('TapHere'));
+        expect(taps, 2);
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsOneWidget);
+        expect(find.text('Item 31'), findsOneWidget);
+      });
+
+      testWidgets('Can be dragged down when not full height', (WidgetTester tester) async {
+        await tester.pumpWidget(_boilerplate(null));
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsOneWidget);
+        expect(find.text('Item 36'), findsNothing);
+
+        await tester.drag(find.text('Item 1'), const Offset(0, 325));
+        await tester.pumpAndSettle();
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsNothing);
+        expect(find.text('Item 36'), findsNothing);
+      });
+
+      testWidgets('Can be dragged up and cover its container and scroll in single motion, and then dragged back down', (WidgetTester tester) async {
+        int taps = 0;
+        await tester.pumpWidget(_boilerplate(() => taps++));
+
+        expect(find.text('TapHere'), findsOneWidget);
+        await tester.tap(find.text('TapHere'));
+        expect(taps, 1);
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsOneWidget);
+        expect(find.text('Item 36'), findsNothing);
+
+        await tester.drag(find.text('Item 1'), const Offset(0, -325));
+        await tester.pumpAndSettle();
+        expect(find.text('TapHere'), findsOneWidget);
+        await tester.tap(find.text('TapHere'));
+        expect(taps, 1);
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsOneWidget);
+        expect(find.text('Item 36'), findsOneWidget);
+
+        await tester.dragFrom(const Offset(20, 20), const Offset(0, 325));
+        await tester.pumpAndSettle();
+        await tester.tap(find.text('TapHere'));
+        expect(taps, 2);
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 18'), findsOneWidget);
+        expect(find.text('Item 36'), findsNothing);
+      });
+
+      testWidgets('Can be flung up gently', (WidgetTester tester) async {
+        int taps = 0;
+        await tester.pumpWidget(_boilerplate(() => taps++));
+
+        expect(find.text('TapHere'), findsOneWidget);
+        await tester.tap(find.text('TapHere'));
+        expect(taps, 1);
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsOneWidget);
+        expect(find.text('Item 36'), findsNothing);
+        expect(find.text('Item 70'), findsNothing);
+
+        await tester.fling(find.text('Item 1'), const Offset(0, -200), 350);
+        await tester.pumpAndSettle();
+        expect(find.text('TapHere'), findsOneWidget);
+        await tester.tap(find.text('TapHere'));
+        expect(taps, 2);
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsOneWidget);
+        expect(find.text('Item 36'), findsOneWidget);
+        expect(find.text('Item 70'), findsNothing);
+      });
+
+      testWidgets('Can be flung up', (WidgetTester tester) async {
+        int taps = 0;
+        await tester.pumpWidget(_boilerplate(() => taps++));
+
+        expect(find.text('TapHere'), findsOneWidget);
+        await tester.tap(find.text('TapHere'));
+        expect(taps, 1);
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsOneWidget);
+        expect(find.text('Item 70'), findsNothing);
+
+        await tester.fling(find.text('Item 1'), const Offset(0, -200), 2000);
+        await tester.pumpAndSettle();
+        expect(find.text('TapHere'), findsOneWidget);
+        await tester.tap(find.text('TapHere'));
+        expect(taps, 1);
+        expect(find.text('Item 1'), findsNothing);
+        expect(find.text('Item 21'), findsNothing);
+        expect(find.text('Item 70'), findsOneWidget);
+      });
+
+      testWidgets('Can be flung down when not full height', (WidgetTester tester) async {
+        await tester.pumpWidget(_boilerplate(null));
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsOneWidget);
+        expect(find.text('Item 36'), findsNothing);
+
+        await tester.fling(find.text('Item 1'), const Offset(0, 325), 2000);
+        await tester.pumpAndSettle();
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsNothing);
+        expect(find.text('Item 36'), findsNothing);
+      });
+
+      testWidgets('Can be flung up and then back down', (WidgetTester tester) async {
+        int taps = 0;
+        await tester.pumpWidget(_boilerplate(() => taps++));
+
+        expect(find.text('TapHere'), findsOneWidget);
+        await tester.tap(find.text('TapHere'));
+        expect(taps, 1);
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsOneWidget);
+        expect(find.text('Item 70'), findsNothing);
+
+        await tester.fling(find.text('Item 1'), const Offset(0, -200), 2000);
+        await tester.pumpAndSettle();
+        expect(find.text('TapHere'), findsOneWidget);
+        await tester.tap(find.text('TapHere'));
+        expect(taps, 1);
+        expect(find.text('Item 1'), findsNothing);
+        expect(find.text('Item 21'), findsNothing);
+        expect(find.text('Item 70'), findsOneWidget);
+
+        await tester.fling(find.text('Item 70'), const Offset(0, 200), 2000);
+        await tester.pumpAndSettle();
+        expect(find.text('TapHere'), findsOneWidget);
+        await tester.tap(find.text('TapHere'));
+        expect(taps, 1);
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsOneWidget);
+        expect(find.text('Item 70'), findsNothing);
+
+        await tester.fling(find.text('Item 1'), const Offset(0, 200), 2000);
+        await tester.pumpAndSettle();
+        expect(find.text('TapHere'), findsOneWidget);
+        await tester.tap(find.text('TapHere'));
+        expect(taps, 2);
+        expect(find.text('Item 1'), findsOneWidget);
+        expect(find.text('Item 21'), findsNothing);
+        expect(find.text('Item 70'), findsNothing);
+      });
+
+      debugDefaultTargetPlatformOverride = null;
+    });
+  }
+}