feat: onSwipe method can cancel the swipe (#9)

CHANGELOG.md

@@ -1,3 +1,10 @@
+## [4.0.0]
+
+- **BREAKING CHANGE**:
+  - CardSwipers onSwipe function now returns ```<bool>``` instead of ```<void>```. If onSwipe returns ```false```,
+    the swipe action will now be canceled and the current card will remain on top of the stack. 
+    Otherwise, if it returns ```true```, the swipe action will be performed as expected.
+
 ## [3.1.0]
 
 - Adds option to set the initial index of the swiper.

README.md

@@ -109,7 +109,7 @@ class Example extends StatelessWidget {
 | isVerticalSwipingEnabled | true    |   Set to ```false``` if you want your card to move only across the horizontal axis when swiping | false
 | isLoop | true | set to ```true``` if the stack should loop | false
 | onTapDisabled | -     |    Function that get triggered when the swiper is disabled | false
-| onSwipe | -    |    Called with the new index and detected swipe direction when the user swiped | false
+| onSwipe | -    |    Called with the oldIndex, newIndex and detected swipe direction when the user swiped.  If [onSwipe] returns ```false```, the swipe action will be canceled. Otherwise, if it returns ```true```, the swipe action will be performed as expected. | false
 | onEnd | -    |    Called when there is no Widget left to be swiped away | false
 | direction | right    |    Direction in which the card is swiped away when triggered from the outside | false
 | numberOfCardsDisplayed | 2    |   If your widgets in the 'cards' list cause performance issues, you can choose to display more cards at a time to reduce how long the user waits for a card to appear | false 

example/lib/main.dart

@@ -76,13 +76,22 @@ class _ExamplePageState extends State<Example> {
     );
   }
 
-  void _onSwipe(
+  bool _onSwipe(
     int? previousIndex,
     int? currentIndex,
     CardSwiperDirection direction,
   ) {
+    if (currentIndex?.isEven == true && direction == CardSwiperDirection.left ||
+        currentIndex?.isOdd == true && direction == CardSwiperDirection.right) {
+      debugPrint(
+        'the card $currentIndex was swiped to the: ${direction.name}; Oh, and also your action got canceled',
+      );
+      return false;
+    }
+
     debugPrint(
       'the card $previousIndex was swiped to the ${direction.name}. Now the card $currentIndex is on top',
     );
+    return true;
   }
 }

lib/src/card_swiper.dart

@@ -38,6 +38,9 @@ class CardSwiper<T extends Widget> extends StatefulWidget {
   final bool isDisabled;
 
   /// function that gets called with the new index and detected swipe direction when the user swiped or swipe is triggered by controller
+  ///
+  /// If [onSwipe] returns false, the swipe action will be canceled and the current card will remain on top of the stack.
+  /// Otherwise, if it returns true, the swipe action will be performed as expected.
   final CardSwiperOnSwipe? onSwipe;
 
   /// function that gets called when there is no widget left to be swiped away
@@ -134,7 +137,9 @@ class _CardSwiperState<T extends Widget> extends State<CardSwiper<T>>
   double get _maxAngle => widget.maxAngle * (pi / 180);
 
   int? _currentIndex;
+
   int? get _nextIndex => getValidIndexOffset(1);
+
   bool get _canSwipe => _currentIndex != null && !widget.isDisabled;
 
   @override
@@ -311,34 +316,55 @@ class _CardSwiperState<T extends Widget> extends State<CardSwiper<T>>
     }
   }
 
+  // handle the onSwipe methode as well as removing the current card from the
+  // stack if onSwipe does not return false
+  void _handleOnSwipe() {
+    setState(() {
+      if (_swipeType == SwipeType.swipe) {
+        final shouldCancelSwipe = widget.onSwipe
+                ?.call(_currentIndex, _nextIndex, detectedDirection) ==
+            false;
+
+        if (shouldCancelSwipe) {
+          return;
+        }
+
+        final previousIndex = _currentIndex;
+        final isLastCard = _currentIndex == widget.cardsCount - 1;
+
+        _currentIndex = _nextIndex;
+        widget.onSwipe?.call(
+          previousIndex,
+          _currentIndex,
+          detectedDirection,
+        );
+
+        if (isLastCard) {
+          widget.onEnd?.call();
+        }
+      }
+    });
+  }
+
+  // reset the card animation
+  void _resetCardAnimation() {
+    setState(() {
+      _animationController.reset();
+      _left = 0;
+      _top = 0;
+      _total = 0;
+      _angle = 0;
+      _scale = widget.scale;
+      _difference = 40;
+      _swipeType = SwipeType.none;
+    });
+  }
+
   //when the status of animation changes
   void _animationStatusListener(AnimationStatus status) {
     if (status == AnimationStatus.completed) {
-      setState(() {
-        if (_swipeType == SwipeType.swipe) {
-          final previousIndex = _currentIndex;
-          final isLastCard = _currentIndex == widget.cardsCount - 1;
-
-          _currentIndex = _nextIndex;
-          widget.onSwipe?.call(
-            previousIndex,
-            _currentIndex,
-            detectedDirection,
-          );
-
-          if (isLastCard) {
-            widget.onEnd?.call();
-          }
-        }
-        _animationController.reset();
-        _left = 0;
-        _top = 0;
-        _total = 0;
-        _angle = 0;
-        _scale = widget.scale;
-        _difference = 40;
-        _swipeType = SwipeType.none;
-      });
+      _handleOnSwipe();
+      _resetCardAnimation();
     }
   }
 

lib/src/typedefs.dart

@@ -1,6 +1,6 @@
 import 'package:flutter_card_swiper/src/enums.dart';
 
-typedef CardSwiperOnSwipe = void Function(
+typedef CardSwiperOnSwipe = bool Function(
   int? previousIndex,
   int? currentIndex,
   CardSwiperDirection direction,

pubspec.yaml

@@ -2,7 +2,7 @@ name: flutter_card_swiper
 description: This is a Tinder-like card swiper package. It allows you to swipe left, right, up, and down and define your own business logic for each direction.
 homepage: https://github.com/ricardodalarme/flutter_card_swiper
 issue_tracker: https://github.com/ricardodalarme/flutter_card_swiper/issues
-version: 3.1.0
+version: 4.0.0
 
 environment:
   sdk: ">=2.12.0 <3.0.0"