chore: add documentation

frontend/app_flowy/packages/flowy_board/lib/src/widgets/board.dart

@@ -95,7 +95,7 @@ class BoardContent extends StatefulWidget {
   ///
   final BoardColumnFooterBuilder? footBuilder;
 
-  final OverlapReorderFlexDragTargetDelegate delegate;
+  final OverlapDragTargetDelegate delegate;
 
   final BoardPhantomController phantomController;
 
@@ -122,15 +122,14 @@ class BoardContent extends StatefulWidget {
 }
 
 class _BoardContentState extends State<BoardContent> {
-  final GlobalKey _columnContainerOverlayKey =
-      GlobalKey(debugLabel: '$BoardContent overlay key');
+  final GlobalKey _columnContainerOverlayKey = GlobalKey(debugLabel: '$BoardContent overlay key');
   late BoardOverlayEntry _overlayEntry;
 
   @override
   void initState() {
     _overlayEntry = BoardOverlayEntry(
       builder: (BuildContext context) {
-        final interceptor = OverlapReorderFlexDragTargetInteceptor(
+        final interceptor = OverlappingDragTargetInteceptor(
           reorderFlexId: widget.dataController.identifier,
           acceptedReorderFlexId: widget.dataController.columnIds,
           delegate: widget.delegate,
@@ -216,8 +215,7 @@ class _BoardColumnDataSourceImpl extends BoardColumnDataDataSource {
   });
 
   @override
-  BoardColumnData get columnData =>
-      dataController.columnController(columnId).columnData;
+  BoardColumnData get columnData => dataController.columnController(columnId).columnData;
 
   @override
   List<String> get acceptedColumnIds => dataController.columnIds;

frontend/app_flowy/packages/flowy_board/lib/src/widgets/flex/drag_state.dart

@@ -46,16 +46,12 @@ class DraggingState {
   final String id;
 
   /// The member of widget.children currently being dragged.
-  ///
-  /// Null if no drag is underway.
   Widget? _draggingWidget;
 
   Widget? get draggingWidget => _draggingWidget;
 
   /// The last computed size of the feedback widget being dragged.
-  Size? _draggingFeedbackSize = Size.zero;
-
-  Size? get feedbackSize => _draggingFeedbackSize;
+  Size? feedbackSize = Size.zero;
 
   /// The location that the dragging widget occupied before it started to drag.
   int dragStartIndex = -1;
@@ -79,15 +75,17 @@ class DraggingState {
   DraggingState(this.id);
 
   Size get dropAreaSize {
-    if (_draggingFeedbackSize == null) {
+    if (feedbackSize == null) {
       return Size.zero;
     }
-    return _draggingFeedbackSize! +
-        const Offset(_dropAreaMargin, _dropAreaMargin);
+    return feedbackSize! + const Offset(_dropAreaMargin, _dropAreaMargin);
   }
 
-  void startDragging(Widget draggingWidget, int draggingWidgetIndex,
-      Size? draggingWidgetSize) {
+  void startDragging(
+    Widget draggingWidget,
+    int draggingWidgetIndex,
+    Size? draggingWidgetSize,
+  ) {
     ///
     assert(draggingWidgetIndex >= 0);
 
@@ -95,7 +93,7 @@ class DraggingState {
     phantomIndex = draggingWidgetIndex;
     dragStartIndex = draggingWidgetIndex;
     currentIndex = draggingWidgetIndex;
-    _draggingFeedbackSize = draggingWidgetSize;
+    feedbackSize = draggingWidgetSize;
   }
 
   void endDragging() {
@@ -130,12 +128,10 @@ class DraggingState {
 
   /// Set the currentIndex to nextIndex
   void moveDragTargetToNext() {
-    Log.trace('moveDragTargetToNext: $nextIndex');
     currentIndex = nextIndex;
   }
 
   void updateNextIndex(int index) {
-    assert(index >= 0);
     Log.trace('updateNextIndex: $index');
     nextIndex = index;
   }

frontend/app_flowy/packages/flowy_board/lib/src/widgets/flex/drag_target.dart

@@ -5,24 +5,18 @@ abstract class DragTargetData {
 }
 
 abstract class ReorderFlexDraggableTargetBuilder {
-  Widget? build<T extends DragTargetData>(
-      BuildContext context,
-      Widget child,
-      DragTargetOnStarted onDragStarted,
-      DragTargetOnEnded<T> onDragEnded,
-      DragTargetWillAccpet<T> onWillAccept);
+  Widget? build<T extends DragTargetData>(BuildContext context, Widget child, DragTargetOnStarted onDragStarted,
+      DragTargetOnEnded<T> onDragEnded, DragTargetWillAccpet<T> onWillAccept);
 }
 
 ///
-typedef DragTargetWillAccpet<T extends DragTargetData> = bool Function(
-    T dragTargetData);
+typedef DragTargetWillAccpet<T extends DragTargetData> = bool Function(T dragTargetData);
 
 ///
 typedef DragTargetOnStarted = void Function(Widget, int, Size?);
 
 ///
-typedef DragTargetOnEnded<T extends DragTargetData> = void Function(
-    T dragTargetData);
+typedef DragTargetOnEnded<T extends DragTargetData> = void Function(T dragTargetData);
 
 /// [ReorderDragTarget] is a [DragTarget] that carries the index information of
 /// the child.
@@ -75,8 +69,7 @@ class ReorderDragTarget<T extends DragTargetData> extends StatefulWidget {
   State<ReorderDragTarget<T>> createState() => _ReorderDragTargetState<T>();
 }
 
-class _ReorderDragTargetState<T extends DragTargetData>
-    extends State<ReorderDragTarget<T>> {
+class _ReorderDragTargetState<T extends DragTargetData> extends State<ReorderDragTarget<T>> {
   /// Returns the dragTarget's size
   Size? _draggingFeedbackSize = Size.zero;
 
@@ -108,8 +101,7 @@ class _ReorderDragTargetState<T extends DragTargetData>
     List<dynamic> rejectedCandidates,
   ) {
     Widget feedbackBuilder = Builder(builder: (BuildContext context) {
-      BoxConstraints contentSizeConstraints =
-          BoxConstraints.loose(_draggingFeedbackSize!);
+      BoxConstraints contentSizeConstraints = BoxConstraints.loose(_draggingFeedbackSize!);
       return _buildDraggableFeedback(
         context,
         contentSizeConstraints,
@@ -149,21 +141,19 @@ class _ReorderDragTargetState<T extends DragTargetData>
           /// When the drag does not end inside a DragTarget widget, the
           /// drag fails, but we still reorder the widget to the last position it
           /// had been dragged to.
-          onDraggableCanceled: (Velocity velocity, Offset offset) =>
-              widget.onDragEnded(widget.dragTargetData),
+          onDraggableCanceled: (Velocity velocity, Offset offset) => widget.onDragEnded(widget.dragTargetData),
           child: widget.child,
         );
 
     return draggableWidget;
   }
 
-  Widget _buildDraggableFeedback(
-      BuildContext context, BoxConstraints constraints, Widget child) {
+  Widget _buildDraggableFeedback(BuildContext context, BoxConstraints constraints, Widget child) {
     return Transform(
       transform: Matrix4.rotationZ(0),
       alignment: FractionalOffset.topLeft,
       child: Material(
-        elevation: 6.0,
+        elevation: 2.0,
         color: Colors.transparent,
         borderRadius: BorderRadius.zero,
         clipBehavior: Clip.hardEdge,
@@ -177,10 +167,6 @@ class DragAnimationController {
   // How long an animation to reorder an element in the list takes.
   final Duration reorderAnimationDuration;
 
-  // How long an animation to scroll to an off-screen element in the
-  // list takes.
-  final Duration scrollAnimationDuration;
-
   // This controls the entrance of the dragging widget into a new place.
   late AnimationController entranceController;
 
@@ -190,14 +176,11 @@ class DragAnimationController {
 
   DragAnimationController({
     required this.reorderAnimationDuration,
-    required this.scrollAnimationDuration,
     required TickerProvider vsync,
     required void Function(AnimationStatus) entranceAnimateStatusChanged,
   }) {
-    entranceController = AnimationController(
-        value: 1.0, vsync: vsync, duration: reorderAnimationDuration);
-    phantomController = AnimationController(
-        value: 0, vsync: vsync, duration: reorderAnimationDuration);
+    entranceController = AnimationController(value: 1.0, vsync: vsync, duration: reorderAnimationDuration);
+    phantomController = AnimationController(value: 0, vsync: vsync, duration: reorderAnimationDuration);
     entranceController.addStatusListener(entranceAnimateStatusChanged);
   }
 
@@ -234,9 +217,7 @@ class IgnorePointerWidget extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final sizedChild = useIntrinsicSize
-        ? child
-        : SizedBox(width: 0.0, height: 0.0, child: child);
+    final sizedChild = useIntrinsicSize ? child : SizedBox(width: 0.0, height: 0.0, child: child);
     return IgnorePointer(
       ignoring: true,
       child: Opacity(
@@ -276,10 +257,8 @@ class PhantomAnimateContorller {
     required this.reorderAnimationDuration,
     required void Function(AnimationStatus) appearAnimateStatusChanged,
   }) {
-    appearController = AnimationController(
-        value: 1.0, vsync: vsync, duration: reorderAnimationDuration);
-    disappearController = AnimationController(
-        value: 0, vsync: vsync, duration: reorderAnimationDuration);
+    appearController = AnimationController(value: 1.0, vsync: vsync, duration: reorderAnimationDuration);
+    disappearController = AnimationController(value: 0, vsync: vsync, duration: reorderAnimationDuration);
     appearController.addStatusListener(appearAnimateStatusChanged);
   }
 
@@ -333,8 +312,7 @@ class FakeDragTarget<T extends DragTargetData> extends StatefulWidget {
   State<FakeDragTarget<T>> createState() => _FakeDragTargetState<T>();
 }
 
-class _FakeDragTargetState<T extends DragTargetData>
-    extends State<FakeDragTarget<T>> {
+class _FakeDragTargetState<T extends DragTargetData> extends State<FakeDragTarget<T>> {
   bool isDragging = false;
 
   @override

frontend/app_flowy/packages/flowy_board/lib/src/widgets/flex/drag_target_inteceptor.dart

@@ -5,9 +5,13 @@ import 'drag_state.dart';
 import 'drag_target.dart';
 import 'reorder_flex.dart';
 
-abstract class ReorderFlexDragTargetInterceptor {
+/// [DragTargetInterceptor] is used to intercept the [DragTarget]'s
+/// [onWillAccept], [OnAccept], and [onLeave] event.
+abstract class DragTargetInterceptor {
+  /// Returns [yes] to receive the [DragTarget]'s event.
   bool canHandler(FlexDragTargetData dragTargetData);
 
+  /// Handle the [DragTarget]'s [onWillAccept] event.
   bool onWillAccept({
     required BuildContext context,
     required ReorderFlexState reorderFlexState,
@@ -16,29 +20,36 @@ abstract class ReorderFlexDragTargetInterceptor {
     required int dragTargetIndex,
   });
 
+  /// Handle the [DragTarget]'s [onAccept] event.
   void onAccept(FlexDragTargetData dragTargetData) {}
 
+  /// Handle the [DragTarget]'s [onLeave] event.
   void onLeave(FlexDragTargetData dragTargetData) {}
 
   ReorderFlexDraggableTargetBuilder? get draggableTargetBuilder => null;
 }
 
-abstract class OverlapReorderFlexDragTargetDelegate {
-  void dragTargetDidDisappear();
-  bool acceptNewDragTargetData(
+abstract class OverlapDragTargetDelegate {
+  void didReturnOriginalDragTarget();
+  void didCrossOtherDragTarget(
     String reorderFlexId,
     FlexDragTargetData dragTargetData,
     int dragTargetIndex,
   );
 }
 
-class OverlapReorderFlexDragTargetInteceptor
-    extends ReorderFlexDragTargetInterceptor {
+/// [OverlappingDragTargetInteceptor] is used to receive the overlapping
+/// [DragTarget] event. If a [DragTarget] child is [DragTarget], it will
+/// receive the [DragTarget] event when being dragged.
+///
+/// Receive the [DragTarget] event if the [acceptedReorderFlexId] contains
+/// the passed in dragTarget' reorderFlexId.
+class OverlappingDragTargetInteceptor extends DragTargetInterceptor {
   final String reorderFlexId;
   final List<String> acceptedReorderFlexId;
-  final OverlapReorderFlexDragTargetDelegate delegate;
+  final OverlapDragTargetDelegate delegate;
 
-  OverlapReorderFlexDragTargetInteceptor({
+  OverlappingDragTargetInteceptor({
     required this.delegate,
     required this.reorderFlexId,
     required this.acceptedReorderFlexId,
@@ -57,9 +68,9 @@ class OverlapReorderFlexDragTargetInteceptor
       required String dragTargetId,
       required int dragTargetIndex}) {
     if (dragTargetId == dragTargetData.reorderFlexId) {
-      delegate.dragTargetDidDisappear();
+      delegate.didReturnOriginalDragTarget();
     } else {
-      delegate.acceptNewDragTargetData(
+      delegate.didCrossOtherDragTarget(
         dragTargetId,
         dragTargetData,
         dragTargetIndex,
@@ -84,8 +95,7 @@ abstract class CrossReorderFlexDragTargetDelegate {
   );
 }
 
-class CrossReorderFlexDragTargetInterceptor
-    extends ReorderFlexDragTargetInterceptor {
+class CrossReorderFlexDragTargetInterceptor extends DragTargetInterceptor {
   final String reorderFlexId;
   final List<String> acceptedReorderFlexIds;
   final CrossReorderFlexDragTargetDelegate delegate;
@@ -117,14 +127,12 @@ class CrossReorderFlexDragTargetInterceptor
 
   @override
   void onAccept(FlexDragTargetData dragTargetData) {
-    Log.trace(
-        '[$CrossReorderFlexDragTargetInterceptor] Column$reorderFlexId on onAccept');
+    Log.trace('[$CrossReorderFlexDragTargetInterceptor] Column$reorderFlexId on onAccept');
   }
 
   @override
   void onLeave(FlexDragTargetData dragTargetData) {
-    Log.trace(
-        '[$CrossReorderFlexDragTargetInterceptor] Column$reorderFlexId on leave');
+    Log.trace('[$CrossReorderFlexDragTargetInterceptor] Column$reorderFlexId on leave');
   }
 
   @override

frontend/app_flowy/packages/flowy_board/lib/src/widgets/flex/reorder_flex.dart

@@ -14,26 +14,34 @@ typedef OnDragEnded = void Function();
 typedef OnReorder = void Function(int fromIndex, int toIndex);
 typedef OnDeleted = void Function(int deletedIndex);
 typedef OnInserted = void Function(int insertedIndex);
-typedef OnReveivePassedInPhantom = void Function(
-    FlexDragTargetData dragTargetData, int phantomIndex);
+typedef OnReveivePassedInPhantom = void Function(FlexDragTargetData dragTargetData, int phantomIndex);
 
 abstract class ReoderFlextDataSource {
+  /// [identifier] represents the id the [ReorderFlex]. It must be unique.
   String get identifier;
+
+  /// The number of [ReoderFlexItem]s will be displaied in the [ReorderFlex].
   UnmodifiableListView<ReoderFlexItem> get items;
 }
 
+/// Each item displaied in the [ReorderFlex] required to implement the [ReoderFlexItem].
 abstract class ReoderFlexItem {
-  /// [id] is used to identify the item
+  /// [id] is used to identify the item. It must be unique.
   String get id;
 }
 
 class ReorderFlexConfig {
-  final bool needsLongPressDraggable = true;
+  /// The opacity of the dragging widget
   final double draggingWidgetOpacity = 0.2;
+
+  // How long an animation to reorder an element
   final Duration reorderAnimationDuration = const Duration(milliseconds: 250);
+
+  // How long an animation to scroll to an off-screen element
   final Duration scrollAnimationDuration = const Duration(milliseconds: 250);
 
   final double? spacing;
+
   const ReorderFlexConfig({this.spacing});
 }
 
@@ -42,17 +50,25 @@ class ReorderFlex extends StatefulWidget {
 
   final List<Widget> children;
   final EdgeInsets? padding;
+
+  /// [direction] How to place the children, default is Axis.vertical
   final Axis direction;
   final MainAxisAlignment mainAxisAlignment = MainAxisAlignment.start;
+
   final ScrollController? scrollController;
 
+  /// [onDragStarted] is called when start dragging
   final OnDragStarted? onDragStarted;
+
+  /// [onReorder] is called when dragTarget did end dragging
   final OnReorder onReorder;
+
+  /// [onDragEnded] is called when dragTarget did end dragging
   final OnDragEnded? onDragEnded;
 
   final ReoderFlextDataSource dataSource;
 
-  final ReorderFlexDragTargetInterceptor? interceptor;
+  final DragTargetInterceptor? interceptor;
 
   const ReorderFlex({
     Key? key,
@@ -74,16 +90,20 @@ class ReorderFlex extends StatefulWidget {
   String get reorderFlexId => dataSource.identifier;
 }
 
-class ReorderFlexState extends State<ReorderFlex>
-    with ReorderFlexMinxi, TickerProviderStateMixin<ReorderFlex> {
+class ReorderFlexState extends State<ReorderFlex> with ReorderFlexMinxi, TickerProviderStateMixin<ReorderFlex> {
   /// Controls scrolls and measures scroll progress.
   late ScrollController _scrollController;
+
+  /// Records the position of the [Scrollable]
   ScrollPosition? _attachedScrollPosition;
 
   /// Whether or not we are currently scrolling this view to show a widget.
   bool _scrolling = false;
 
+  /// [dragState] records the dragging state including dragStartIndex, and phantomIndex, etc.
   late DraggingState dragState;
+
+  /// [_dragAnimationController] controls the dragging animations
   late DragAnimationController _dragAnimationController;
 
   @override
@@ -92,7 +112,6 @@ class ReorderFlexState extends State<ReorderFlex>
 
     _dragAnimationController = DragAnimationController(
       reorderAnimationDuration: widget.config.reorderAnimationDuration,
-      scrollAnimationDuration: widget.config.scrollAnimationDuration,
       entranceAnimateStatusChanged: (status) {
         if (status == AnimationStatus.completed) {
           setState(() => _requestAnimationToNextIndex());
@@ -111,9 +130,7 @@ class ReorderFlexState extends State<ReorderFlex>
       _attachedScrollPosition = null;
     }
 
-    _scrollController = widget.scrollController ??
-        PrimaryScrollController.of(context) ??
-        ScrollController();
+    _scrollController = widget.scrollController ?? PrimaryScrollController.of(context) ?? ScrollController();
 
     if (_scrollController.hasClients) {
       _attachedScrollPosition = Scrollable.of(context)?.position;
@@ -235,9 +252,7 @@ class ReorderFlexState extends State<ReorderFlex>
             ]);
           } else if (childIndex == dragPhantomIndex) {
             return _buildDraggingContainer(
-                children: shiftedIndex <= childIndex
-                    ? [dragTarget, disappearSpace]
-                    : [disappearSpace, dragTarget]);
+                children: shiftedIndex <= childIndex ? [dragTarget, disappearSpace] : [disappearSpace, dragTarget]);
           }
         }
 
@@ -258,9 +273,7 @@ class ReorderFlexState extends State<ReorderFlex>
             ]);
           } else if (childIndex == dragPhantomIndex) {
             return _buildDraggingContainer(
-                children: shiftedIndex >= childIndex
-                    ? [disappearSpace, dragTarget]
-                    : [dragTarget, disappearSpace]);
+                children: shiftedIndex >= childIndex ? [disappearSpace, dragTarget] : [dragTarget, disappearSpace]);
           }
         }
 
@@ -286,8 +299,7 @@ class ReorderFlexState extends State<ReorderFlex>
     Widget child,
     int dragTargetIndex,
   ) {
-    final ReoderFlexItem reorderFlexItem =
-        widget.dataSource.items[dragTargetIndex];
+    final ReoderFlexItem reorderFlexItem = widget.dataSource.items[dragTargetIndex];
     return ReorderDragTarget<FlexDragTargetData>(
       dragTargetData: FlexDragTargetData(
         draggingIndex: dragTargetIndex,
@@ -297,14 +309,12 @@ class ReorderFlexState extends State<ReorderFlex>
         dragTargetId: reorderFlexItem.id,
       ),
       onDragStarted: (draggingWidget, draggingIndex, size) {
-        Log.debug(
-            "[DragTarget] Column${widget.dataSource.identifier} start dragging");
+        Log.debug("[DragTarget] Column${widget.dataSource.identifier} start dragging");
         _startDragging(draggingWidget, draggingIndex, size);
         widget.onDragStarted?.call(draggingIndex);
       },
       onDragEnded: (dragTargetData) {
-        Log.debug(
-            "[DragTarget]: Column${widget.dataSource.identifier} end dragging");
+        Log.debug("[DragTarget]: Column${widget.dataSource.identifier} end dragging");
 
         setState(() {
           _onReordered(
@@ -352,7 +362,7 @@ class ReorderFlexState extends State<ReorderFlex>
 
   bool _interceptDragTarget(
     FlexDragTargetData dragTargetData,
-    void Function(ReorderFlexDragTargetInterceptor) callback,
+    void Function(DragTargetInterceptor) callback,
   ) {
     final interceptor = widget.interceptor;
     if (interceptor != null && interceptor.canHandler(dragTargetData)) {
@@ -401,8 +411,7 @@ class ReorderFlexState extends State<ReorderFlex>
     Log.trace(
         '[$ReorderDragTarget] ${widget.dataSource.identifier} on will accept, dragIndex:$dragIndex, dragTargetIndex:$dragTargetIndex, count: ${widget.dataSource.items.length}');
 
-    bool willAccept =
-        dragState.dragStartIndex == dragIndex && dragIndex != dragTargetIndex;
+    bool willAccept = dragState.dragStartIndex == dragIndex && dragIndex != dragTargetIndex;
     setState(() {
       if (willAccept) {
         int shiftedIndex = dragState.calculateShiftedIndex(dragTargetIndex);
@@ -429,8 +438,7 @@ class ReorderFlexState extends State<ReorderFlex>
   }
 
   Widget _wrapScrollView({required Widget child}) {
-    if (widget.scrollController != null &&
-        PrimaryScrollController.of(context) == null) {
+    if (widget.scrollController != null && PrimaryScrollController.of(context) == null) {
       return child;
     } else {
       return SingleChildScrollView(
@@ -484,14 +492,12 @@ class ReorderFlexState extends State<ReorderFlex>
   void _scrollTo(BuildContext context) {
     if (_scrolling) return;
     final RenderObject contextObject = context.findRenderObject()!;
-    final RenderAbstractViewport viewport =
-        RenderAbstractViewport.of(contextObject)!;
+    final RenderAbstractViewport viewport = RenderAbstractViewport.of(contextObject)!;
     // If and only if the current scroll offset falls in-between the offsets
     // necessary to reveal the selected context at the top or bottom of the
     // screen, then it is already on-screen.
-    final double margin = widget.direction == Axis.horizontal
-        ? dragState.dropAreaSize.width
-        : dragState.dropAreaSize.height;
+    final double margin =
+        widget.direction == Axis.horizontal ? dragState.dropAreaSize.width : dragState.dropAreaSize.height;
     if (_scrollController.hasClients) {
       final double scrollOffset = _scrollController.offset;
       final double topOffset = max(
@@ -502,8 +508,7 @@ class ReorderFlexState extends State<ReorderFlex>
         _scrollController.position.maxScrollExtent,
         viewport.getOffsetToReveal(contextObject, 1.0).offset + margin,
       );
-      final bool onScreen =
-          scrollOffset <= topOffset && scrollOffset >= bottomOffset;
+      final bool onScreen = scrollOffset <= topOffset && scrollOffset >= bottomOffset;
 
       // If the context is off screen, then we request a scroll to make it visible.
       if (!onScreen) {
@@ -511,7 +516,7 @@ class ReorderFlexState extends State<ReorderFlex>
         _scrollController.position
             .animateTo(
           scrollOffset < bottomOffset ? bottomOffset : topOffset,
-          duration: _dragAnimationController.scrollAnimationDuration,
+          duration: widget.config.scrollAnimationDuration,
           curve: Curves.easeInOut,
         )
             .then((void value) {

frontend/app_flowy/packages/flowy_board/lib/src/widgets/phantom/phantom_controller.dart

@@ -34,8 +34,7 @@ abstract class BoardPhantomControllerDelegate {
   );
 }
 
-class BoardPhantomController extends OverlapReorderFlexDragTargetDelegate
-    with CrossReorderFlexDragTargetDelegate {
+class BoardPhantomController extends OverlapDragTargetDelegate with CrossReorderFlexDragTargetDelegate {
   PhantomRecord? phantomRecord;
   final BoardPhantomControllerDelegate delegate;
   final columnsState = ColumnPhantomStateController();
@@ -117,8 +116,7 @@ class BoardPhantomController extends OverlapReorderFlexDragTargetDelegate
 
     WidgetsBinding.instance.addPostFrameCallback((_) {
       Future.delayed(const Duration(milliseconds: 100), () {
-        Log.debug(
-            '[$BoardPhantomController] notify $toColumnId to insert phantom');
+        Log.debug('[$BoardPhantomController] notify $toColumnId to insert phantom');
         columnsState.notifyDidInsertPhantom(toColumnId);
       });
     });
@@ -185,7 +183,7 @@ class BoardPhantomController extends OverlapReorderFlexDragTargetDelegate
   }
 
   @override
-  void dragTargetDidDisappear() {
+  void didReturnOriginalDragTarget() {
     if (phantomRecord == null) {
       return;
     }
@@ -193,6 +191,19 @@ class BoardPhantomController extends OverlapReorderFlexDragTargetDelegate
     _removePhantom(phantomRecord!.toColumnId);
     phantomRecord = null;
   }
+
+  @override
+  void didCrossOtherDragTarget(
+    String reorderFlexId,
+    FlexDragTargetData dragTargetData,
+    int dragTargetIndex,
+  ) {
+    acceptNewDragTargetData(
+      reorderFlexId,
+      dragTargetData,
+      dragTargetIndex,
+    );
+  }
 }
 
 /// Use [PhantomRecord] to record where to remove the column item and where to
@@ -221,8 +232,7 @@ class PhantomRecord {
     if (fromColumnIndex == index) {
       return;
     }
-    Log.debug(
-        '[$PhantomRecord] Update Column$fromColumnId remove position to $index');
+    Log.debug('[$PhantomRecord] Update Column$fromColumnId remove position to $index');
     fromColumnIndex = index;
   }
 
@@ -231,8 +241,7 @@ class PhantomRecord {
       return;
     }
 
-    Log.debug(
-        '[$PhantomRecord] Column$toColumnId update position $toColumnIndex -> $index');
+    Log.debug('[$PhantomRecord] Column$toColumnId update position $toColumnIndex -> $index');
     toColumnIndex = index;
   }
 
@@ -245,8 +254,7 @@ class PhantomRecord {
 class PhantomColumnItem extends ColumnItem {
   final PassthroughPhantomContext phantomContext;
 
-  PhantomColumnItem(PassthroughPhantomContext insertedPhantom)
-      : phantomContext = insertedPhantom;
+  PhantomColumnItem(PassthroughPhantomContext insertedPhantom) : phantomContext = insertedPhantom;
 
   @override
   bool get isPhantom => true;
@@ -256,9 +264,8 @@ class PhantomColumnItem extends ColumnItem {
 
   Size? get feedbackSize => phantomContext.feedbackSize;
 
-  Widget get draggingWidget => phantomContext.draggingWidget == null
-      ? const SizedBox()
-      : phantomContext.draggingWidget!;
+  Widget get draggingWidget =>
+      phantomContext.draggingWidget == null ? const SizedBox() : phantomContext.draggingWidget!;
 
   @override
   String toString() {

frontend/app_flowy/packages/flowy_board/lib/src/widgets/phantom/phantom_state.dart

@@ -97,13 +97,7 @@ class PhantomInsertNotifier extends ChangeNotifier {
 }
 
 class PhantomDeleteNotifier extends ChangeNotifier {
-  // int deletedIndex = -1;
-
   void remove() {
-    // if (this.deletedIndex != deletedIndex) {
-    //   this.deletedIndex = deletedIndex;
-    //   notifyListeners();
-    // }
     notifyListeners();
   }
 }