From d1136e31090ca1191c8f3ffe483931ba083fc5cd Mon Sep 17 00:00:00 2001
From: Sander Kersten <spkersten@gmail.com>
Date: Thu, 21 Feb 2019 00:42:15 +0100
Subject: [PATCH] Fix issue where SliverPersistentHeader that is both floating
 and pinned would scroll down when scrolling past the beginning of the
 ScrollView (#27433)

---
 .../rendering/sliver_persistent_header.dart   |   1 +
 .../slivers_appbar_floating_pinned_test.dart  | 102 ++++++++++++++++++
 2 files changed, 103 insertions(+)

diff --git a/packages/flutter/lib/src/rendering/sliver_persistent_header.dart b/packages/flutter/lib/src/rendering/sliver_persistent_header.dart
index a00a684cb4..84a9b0ce2f 100644
--- a/packages/flutter/lib/src/rendering/sliver_persistent_header.dart
+++ b/packages/flutter/lib/src/rendering/sliver_persistent_header.dart
@@ -524,6 +524,7 @@ abstract class RenderSliverFloatingPinnedPersistentHeader extends RenderSliverFl
     final double layoutExtent = maxExtent - constraints.scrollOffset;
     geometry = SliverGeometry(
       scrollExtent: maxExtent,
+      paintOrigin: math.min(constraints.overlap, 0.0),
       paintExtent: clampedPaintExtent,
       layoutExtent: layoutExtent.clamp(0.0, clampedPaintExtent),
       maxPaintExtent: maxExtent,
diff --git a/packages/flutter/test/widgets/slivers_appbar_floating_pinned_test.dart b/packages/flutter/test/widgets/slivers_appbar_floating_pinned_test.dart
index 69614fec7f..563920b561 100644
--- a/packages/flutter/test/widgets/slivers_appbar_floating_pinned_test.dart
+++ b/packages/flutter/test/widgets/slivers_appbar_floating_pinned_test.dart
@@ -112,4 +112,106 @@ void main() {
     expect(render.geometry.paintExtent, availableHeight);
     expect(render.geometry.layoutExtent, 0.0);
   });
+
+  testWidgets('Pinned and floating SliverAppBar sticks to top the content is scroll down', (WidgetTester tester) async {
+    const Key anchor = Key('drag');
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Center(
+          child: Container(
+            height: 300,
+            color: Colors.green,
+            child: CustomScrollView(
+              physics: const BouncingScrollPhysics(),
+              slivers: <Widget>[
+                const SliverAppBar(
+                  pinned: true,
+                  floating: true,
+                  expandedHeight: 100.0,
+                ),
+                SliverToBoxAdapter(child: Container(key: anchor, color: Colors.red, height: 100)),
+                SliverToBoxAdapter(child: Container(height: 600, color: Colors.green)),
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+    final RenderSliverFloatingPinnedPersistentHeader render = tester.renderObject(find.byType(SliverAppBar));
+
+    const double scrollDistance = 40;
+    final TestGesture gesture = await tester.press(find.byKey(anchor));
+    await gesture.moveBy(const Offset(0, scrollDistance));
+    await tester.pump();
+
+    expect(render.geometry.paintOrigin, -scrollDistance);
+  });
+
+  testWidgets('Floating SliverAppBar sticks to top the content is scroll down', (WidgetTester tester) async {
+    const Key anchor = Key('drag');
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Center(
+          child: Container(
+            height: 300,
+            color: Colors.green,
+            child: CustomScrollView(
+              physics: const BouncingScrollPhysics(),
+              slivers: <Widget>[
+                const SliverAppBar(
+                  pinned: false,
+                  floating: true,
+                  expandedHeight: 100.0,
+                ),
+                SliverToBoxAdapter(child: Container(key: anchor, color: Colors.red, height: 100)),
+                SliverToBoxAdapter(child: Container(height: 600, color: Colors.green)),
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+    final RenderSliverFloatingPersistentHeader render = tester.renderObject(find.byType(SliverAppBar));
+
+    const double scrollDistance = 40;
+    final TestGesture gesture = await tester.press(find.byKey(anchor));
+    await gesture.moveBy(const Offset(0, scrollDistance));
+    await tester.pump();
+
+    expect(render.geometry.paintOrigin, -scrollDistance);
+  });
+
+  testWidgets('Pinned SliverAppBar sticks to top the content is scroll down', (WidgetTester tester) async {
+    const Key anchor = Key('drag');
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Center(
+          child: Container(
+            height: 300,
+            color: Colors.green,
+            child: CustomScrollView(
+              physics: const BouncingScrollPhysics(),
+              slivers: <Widget>[
+                const SliverAppBar(
+                  pinned: true,
+                  floating: false,
+                  expandedHeight: 100.0,
+                ),
+                SliverToBoxAdapter(child: Container(key: anchor, color: Colors.red, height: 100)),
+                SliverToBoxAdapter(child: Container(height: 600, color: Colors.green)),
+              ],
+            ),
+          ),
+        ),
+      ),
+    );
+    final RenderSliverPinnedPersistentHeader render = tester.renderObject(find.byType(SliverAppBar));
+
+    const double scrollDistance = 40;
+    final TestGesture gesture = await tester.press(find.byKey(anchor));
+    await gesture.moveBy(const Offset(0, scrollDistance));
+    await tester.pump();
+
+    expect(render.geometry.paintOrigin, -scrollDistance);
+  });
 }