RefreshIndicator can be shown when dragging from non-zero scroll position (#71303)

dev/integration_tests/flutter_gallery/lib/demo/material/overscroll_demo.dart

@@ -27,8 +27,10 @@ class OverscrollDemoState extends State<OverscrollDemo> {
 
   Future<void> _handleRefresh() {
     final Completer<void> completer = Completer<void>();
-    Timer(const Duration(seconds: 3), () { completer.complete(); });
+    Timer(const Duration(seconds: 3), () => completer.complete());
     return completer.future.then((_) {
+      if (!mounted)
+        return;
       ScaffoldMessenger.of(context).showSnackBar(SnackBar(
         content: const Text('Refresh complete'),
         action: SnackBarAction(

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

@@ -218,7 +218,8 @@ class RefreshIndicatorState extends State<RefreshIndicator> with TickerProviderS
   bool _handleScrollNotification(ScrollNotification notification) {
     if (!widget.notificationPredicate(notification))
       return false;
-    if (notification is ScrollStartNotification && notification.metrics.extentBefore == 0.0 &&
+    if ((notification is ScrollStartNotification || notification is ScrollUpdateNotification) &&
+        notification.metrics.extentBefore == 0.0 &&
         _mode == null && _start(notification.metrics.axisDirection)) {
       setState(() {
         _mode = _RefreshIndicatorMode.drag;

packages/flutter/test/material/refresh_indicator_test.dart

@@ -88,7 +88,6 @@ void main() {
     await tester.pump(const Duration(seconds: 1)); // finish the indicator hide animation
     expect(refreshCalled, false);
 
-
     await tester.fling(find.text('A'), const Offset(0.0, 300.0), 1000.0); // vertical fling
     await tester.pump();
     await tester.pump(const Duration(seconds: 1)); // finish the scroll animation
@@ -501,4 +500,73 @@ void main() {
         4.0,
     );
   });
+
+  testWidgets('Top RefreshIndicator showed when dragging from non-zero scroll position', (WidgetTester tester) async {
+    refreshCalled = false;
+    final ScrollController scrollController = ScrollController();
+    await tester.pumpWidget(
+      MaterialApp(
+        home: RefreshIndicator(
+          onRefresh: holdRefresh,
+          child: ListView(
+            controller: scrollController,
+            physics: const AlwaysScrollableScrollPhysics(),
+            children: const <Widget>[
+              SizedBox(
+                height: 200.0,
+                child: Text('X'),
+              ),
+              SizedBox(
+                height: 800.0,
+                child: Text('Y'),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    scrollController.jumpTo(50.0);
+
+    await tester.fling(find.text('X'), const Offset(0.0, 300.0), 1000.0);
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1)); // finish the scroll animation
+    await tester.pump(const Duration(seconds: 1)); // finish the indicator settle animation
+    expect(tester.getCenter(find.byType(RefreshProgressIndicator)).dy, lessThan(300.0));
+  });
+
+  testWidgets('Bottom RefreshIndicator showed when dragging from non-zero scroll position', (WidgetTester tester) async {
+    refreshCalled = false;
+    final ScrollController scrollController = ScrollController();
+    await tester.pumpWidget(
+      MaterialApp(
+        home: RefreshIndicator(
+          onRefresh: holdRefresh,
+          child: ListView(
+            reverse: true,
+            controller: scrollController,
+            physics: const AlwaysScrollableScrollPhysics(),
+            children: const <Widget>[
+              SizedBox(
+                height: 200.0,
+                child: Text('X'),
+              ),
+              SizedBox(
+                height: 800.0,
+                child: Text('Y'),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    scrollController.jumpTo(50.0);
+
+    await tester.fling(find.text('X'), const Offset(0.0, -300.0), 1000.0);
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1)); // finish the scroll animation
+    await tester.pump(const Duration(seconds: 1)); // finish the indicator settle animation
+    expect(tester.getCenter(find.byType(RefreshProgressIndicator)).dy, greaterThan(300.0));
+  });
 }