Fix refresh cancelation (#139535)

Changes drag release logic so that an armed refresh is only canceled if the user has scrolled back up beyond the point where the refresh indicator was armed. (Fixes https://github.com/flutter/flutter/issues/138848.)

This is the minimal change I found could be made to restore something like the behavior that I would expect.

This may still need a bit of work, because it only masks the second issue I mentioned, that releasing a drag can cause the scroll position to be animated back up from the release point. There is actually a bug about that: https://github.com/flutter/flutter/issues/6052. I would like to see that bug fixed too. This PR doesn't address that, but makes it harder to hit that issue.

@Piinks this is a recreation of #139015 (since I couldn't figure out some issue with a git detached branch, so I fixed the PR and I'm re-submitting it). This version includes one line that was somehow accidentally dropped from the original PR. This will hopefully fix the test failures.

However, I don't have a clue how to write a test for a Flutter UI widget. I'll try to figure that out, but also I don't have a lot of time to work on this. I would appreciate at least some user testing to verify that the new behavior is much more intuitive than the old behavior.

- [?] All existing and new tests are passing.

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

@@ -372,10 +372,6 @@ class RefreshIndicatorState extends State<RefreshIndicator> with TickerProviderS
       }
     } else if (notification is ScrollUpdateNotification) {
       if (_mode == _RefreshIndicatorMode.drag || _mode == _RefreshIndicatorMode.armed) {
-        if ((notification.metrics.axisDirection  == AxisDirection.down && notification.metrics.extentBefore > 0.0)
-            || (notification.metrics.axisDirection  == AxisDirection.up && notification.metrics.extentAfter > 0.0)) {
-          _dismiss(_RefreshIndicatorMode.canceled);
-        } else {
         if (notification.metrics.axisDirection == AxisDirection.down) {
           _dragOffset = _dragOffset! - notification.scrollDelta!;
         } else if (notification.metrics.axisDirection == AxisDirection.up) {
@@ -383,7 +379,6 @@ class RefreshIndicatorState extends State<RefreshIndicator> with TickerProviderS
         }
         _checkDragOffset(notification.metrics.viewportDimension);
       }
-      }
       if (_mode == _RefreshIndicatorMode.armed && notification.dragDetails == null) {
         // On iOS start the refresh when the Scrollable bounces back from the
         // overscroll (ScrollNotification indicating this don't have dragDetails
@@ -402,7 +397,11 @@ class RefreshIndicatorState extends State<RefreshIndicator> with TickerProviderS
     } else if (notification is ScrollEndNotification) {
       switch (_mode) {
         case _RefreshIndicatorMode.armed:
+          if (_positionController.value < 1.0) {
+            _dismiss(_RefreshIndicatorMode.canceled);
+          } else {
             _show();
+          }
         case _RefreshIndicatorMode.drag:
           _dismiss(_RefreshIndicatorMode.canceled);
         case _RefreshIndicatorMode.canceled:

packages/flutter/test/material/refresh_indicator_test.dart

@@ -252,7 +252,7 @@ void main() {
       ),
     );
 
-    await tester.fling(find.text('X'), const Offset(0.0, 100.0), 1000.0);
+    await tester.fling(find.text('X'), const Offset(0.0, 200.0), 1000.0);
     await tester.pump();
     await tester.pump(const Duration(seconds: 1));
     await tester.pump(const Duration(seconds: 1));
@@ -260,6 +260,76 @@ void main() {
     expect(refreshCalled, true);
   });
 
+  testWidgets('RefreshIndicator - drag back not far enough to cancel', (WidgetTester tester) async {
+    refreshCalled = false;
+    await tester.pumpWidget(
+      MaterialApp(
+        home: RefreshIndicator(
+          onRefresh: refresh,
+          child: ListView(
+            physics: const AlwaysScrollableScrollPhysics(),
+            children: const <Widget>[
+              SizedBox(
+                height: 200.0,
+                child: Text('X'),
+              ),
+              SizedBox(height: 1000),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    final Offset startLocation = tester.getCenter(find.text('X'), warnIfMissed: true, callee: 'drag');
+    final TestPointer testPointer = TestPointer();
+    await tester.sendEventToBinding(testPointer.down(startLocation));
+    await tester.sendEventToBinding(testPointer.move(startLocation + const Offset(0.0, 175)));
+    await tester.pump();
+    await tester.sendEventToBinding(testPointer.move(startLocation + const Offset(0.0, 150)));
+    await tester.pump();
+    await tester.sendEventToBinding(testPointer.up());
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1));
+    await tester.pump(const Duration(seconds: 1));
+    await tester.pump(const Duration(seconds: 1));
+    expect(refreshCalled, true);
+  });
+
+  testWidgets('RefreshIndicator - drag back far enough to cancel', (WidgetTester tester) async {
+    refreshCalled = false;
+    await tester.pumpWidget(
+      MaterialApp(
+        home: RefreshIndicator(
+          onRefresh: refresh,
+          child: ListView(
+            physics: const AlwaysScrollableScrollPhysics(),
+            children: const <Widget>[
+              SizedBox(
+                height: 200.0,
+                child: Text('X'),
+              ),
+              SizedBox(height: 1000),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    final Offset startLocation = tester.getCenter(find.text('X'), warnIfMissed: true, callee: 'drag');
+    final TestPointer testPointer = TestPointer();
+    await tester.sendEventToBinding(testPointer.down(startLocation));
+    await tester.sendEventToBinding(testPointer.move(startLocation + const Offset(0.0, 175)));
+    await tester.pump();
+    await tester.sendEventToBinding(testPointer.move(startLocation + const Offset(0.0, 149)));
+    await tester.pump();
+    await tester.sendEventToBinding(testPointer.up());
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1));
+    await tester.pump(const Duration(seconds: 1));
+    await tester.pump(const Duration(seconds: 1));
+    expect(refreshCalled, false);
+  });
+
   testWidgets('RefreshIndicator - show - slow', (WidgetTester tester) async {
     refreshCalled = false;
     await tester.pumpWidget(