Fix DragTarget not being rebuilt when a rejected Draggable enters #38786 (#38789)

packages/flutter/lib/src/widgets/drag_target.dart

@@ -524,9 +524,12 @@ class _DragTargetState<T> extends State<DragTarget<T>> {
         _candidateAvatars.add(avatar);
       });
       return true;
+    } else {
+      setState(() {
+        _rejectedAvatars.add(avatar);
+      });
+      return false;
     }
-    _rejectedAvatars.add(avatar);
-    return false;
   }
 
   void didLeave(_DragAvatar<dynamic> avatar) {

packages/flutter/test/widgets/draggable_test.dart

@@ -972,6 +972,144 @@ void main() {
             Offset(secondLocation.dx, secondLocation.dy - firstLocation.dy)));
   });
 
+  testWidgets('Drag and drop - DragTarget rebuilds with and without rejected data when a rejected draggable enters and leaves', (WidgetTester tester) async {
+    await tester.pumpWidget(MaterialApp(
+      home: Column(
+        children: <Widget>[
+          const Draggable<int>(
+            data: 1,
+            child: Text('Source'),
+            feedback: Text('Dragging'),
+          ),
+          DragTarget<int>(
+            builder:
+                (BuildContext context, List<int> data, List<dynamic> rejects) {
+              return Container(
+                height: 100.0,
+                child: rejects.isNotEmpty
+                    ? const Text('Rejected')
+                    : const Text('Target'),
+              );
+            },
+            onWillAccept: (int data) => false,
+          ),
+        ],
+      ),
+    ));
+
+    expect(find.text('Dragging'), findsNothing);
+    expect(find.text('Target'), findsOneWidget);
+    expect(find.text('Rejected'), findsNothing);
+
+    final Offset firstLocation = tester.getTopLeft(find.text('Source'));
+    final TestGesture gesture =
+    await tester.startGesture(firstLocation, pointer: 7);
+    await tester.pump();
+
+    expect(find.text('Dragging'), findsOneWidget);
+    expect(find.text('Target'), findsOneWidget);
+    expect(find.text('Rejected'), findsNothing);
+
+    final Offset secondLocation = tester.getCenter(find.text('Target'));
+    await gesture.moveTo(secondLocation);
+    await tester.pump();
+
+    expect(find.text('Dragging'), findsOneWidget);
+    expect(find.text('Target'), findsNothing);
+    expect(find.text('Rejected'), findsOneWidget);
+
+    await gesture.moveTo(firstLocation);
+    await tester.pump();
+
+    expect(find.text('Dragging'), findsOneWidget);
+    expect(find.text('Target'), findsOneWidget);
+    expect(find.text('Rejected'), findsNothing);
+  });
+
+
+  testWidgets('Drag and drop - Can drag and drop over a non-accepting target multiple times', (WidgetTester tester) async {
+    int numberOfTimesOnDraggableCanceledCalled = 0;
+    await tester.pumpWidget(MaterialApp(
+      home: Column(
+        children: <Widget>[
+          Draggable<int>(
+            data: 1,
+            child: const Text('Source'),
+            feedback: const Text('Dragging'),
+          onDraggableCanceled: (Velocity velocity, Offset offset) {
+            numberOfTimesOnDraggableCanceledCalled++;
+          },
+          ),
+          DragTarget<int>(
+            builder:
+                (BuildContext context, List<int> data, List<dynamic> rejects) {
+              return Container(
+                height: 100.0,
+                child: rejects.isNotEmpty
+                    ? const Text('Rejected')
+                    : const Text('Target'),
+              );
+            },
+            onWillAccept: (int data) => false,
+          ),
+        ],
+      ),
+    ));
+
+    expect(find.text('Dragging'), findsNothing);
+    expect(find.text('Target'), findsOneWidget);
+    expect(find.text('Rejected'), findsNothing);
+
+    final Offset firstLocation = tester.getTopLeft(find.text('Source'));
+    final TestGesture gesture =
+    await tester.startGesture(firstLocation, pointer: 7);
+    await tester.pump();
+
+    expect(find.text('Dragging'), findsOneWidget);
+    expect(find.text('Target'), findsOneWidget);
+    expect(find.text('Rejected'), findsNothing);
+
+    final Offset secondLocation = tester.getCenter(find.text('Target'));
+    await gesture.moveTo(secondLocation);
+    await tester.pump();
+
+    expect(find.text('Dragging'), findsOneWidget);
+    expect(find.text('Target'), findsNothing);
+    expect(find.text('Rejected'), findsOneWidget);
+
+    await gesture.up();
+    await tester.pump();
+
+    expect(find.text('Dragging'), findsNothing);
+    expect(find.text('Target'), findsOneWidget);
+    expect(find.text('Rejected'), findsNothing);
+    expect(numberOfTimesOnDraggableCanceledCalled, 1);
+
+    // Drag and drop the Draggable onto the Target a second time.
+    final TestGesture secondGesture =
+    await tester.startGesture(firstLocation, pointer: 7);
+    await tester.pump();
+
+    expect(find.text('Dragging'), findsOneWidget);
+    expect(find.text('Target'), findsOneWidget);
+    expect(find.text('Rejected'), findsNothing);
+
+    await secondGesture.moveTo(secondLocation);
+    await tester.pump();
+
+    expect(find.text('Dragging'), findsOneWidget);
+    expect(find.text('Target'), findsNothing);
+    expect(find.text('Rejected'), findsOneWidget);
+
+    await secondGesture.up();
+    await tester.pump();
+
+    expect(numberOfTimesOnDraggableCanceledCalled, 2);
+    expect(find.text('Dragging'), findsNothing);
+    expect(find.text('Target'), findsOneWidget);
+    expect(find.text('Rejected'), findsNothing);
+  });
+
   testWidgets('Drag and drop - onDragCompleted not called if dropped on non-accepting target', (WidgetTester tester) async {
     final List<int> accepted = <int>[];
     bool onDragCompletedCalled = false;