Add max offset listener

lib/src/swipeable.dart

@@ -19,6 +19,8 @@ typedef SwipeDirectionCallback = void Function(SwipeDirection direction);
 /// Used by [Swipeable.confirmSwipe].
 typedef ConfirmSwipeCallback = Future<bool> Function(SwipeDirection direction);
 
+typedef OnOverScrollTheMaxOffset = void Function();
+
 /// The direction in which a [Swipeable] can be swiped.
 enum SwipeDirection {
   /// The [Swipeable] can be swiped by dragging either left or right.
@@ -58,11 +60,13 @@ class Swipeable extends StatefulWidget {
     this.movementDuration = const Duration(milliseconds: 200),
     this.crossAxisEndOffset = 0.0,
     this.dragStartBehavior = DragStartBehavior.start,
+    this.swipeIntensity = 1.0,
     this.allowedPointerKinds = const {
       PointerDeviceKind.invertedStylus,
       PointerDeviceKind.stylus,
       PointerDeviceKind.touch
     },
+    this.onOverScrollTheMaxOffset,
   })  : assert(secondaryBackground == null || background != null),
         super(key: key);
 
@@ -154,6 +158,13 @@ class Swipeable extends StatefulWidget {
   ///  * [DragGestureRecognizer.dragStartBehavior], which gives an example for the different behaviors.
   final DragStartBehavior dragStartBehavior;
 
+  ///If the swipeIntensity is low, the message requires a stronger swipe. 
+  ///The default value is set to 1. Consider increasing the swipeIntensity to make it easier for users to swipe.
+  final double swipeIntensity;
+
+  /// When the user scrolls beyond the maximum offset, the function will be invoked, and it will only be called once.
+  final OnOverScrollTheMaxOffset? onOverScrollTheMaxOffset;
+
   @override
   _SwipeableState createState() => _SwipeableState();
 }
@@ -191,6 +202,19 @@ class _SwipeableState extends State<Swipeable> with TickerProviderStateMixin, Au
     _moveController = AnimationController(duration: widget.movementDuration, vsync: this)
       ..addStatusListener(_handleDismissStatusChanged);
     _updateMoveAnimation();
+    _moveController.addListener(() {
+      
+      if (!isInSwipe) {
+        isSwipeAnimationRunning = true;
+      }
+      
+      if (isSwipeAnimationRunning && _moveController.value >= widget.maxOffset) {
+        if (widget.onOverScrollTheMaxOffset != null) {
+          widget.onOverScrollTheMaxOffset!();
+        }
+        isSwipeAnimationRunning = false;
+      }
+    });
 
     super.initState();
   }
@@ -199,6 +223,7 @@ class _SwipeableState extends State<Swipeable> with TickerProviderStateMixin, Au
   late Animation<Offset> _moveAnimation;
 
   double _dragExtent = 0.0;
+  bool isSwipeAnimationRunning = false;
   bool _dragUnderway = false;
   Size? _sizePriorToCollapse;
 
@@ -207,6 +232,8 @@ class _SwipeableState extends State<Swipeable> with TickerProviderStateMixin, Au
   @override
   bool get wantKeepAlive => _moveController.isAnimating == true;
 
+  bool get isInSwipe => _moveController.value != 0;
+
   @override
   void dispose() {
     _moveController.dispose();
@@ -261,7 +288,7 @@ class _SwipeableState extends State<Swipeable> with TickerProviderStateMixin, Au
       return;
     }
 
-    final delta = details.primaryDelta ?? 0.0;
+    final delta = (details.primaryDelta ?? 0.0) * widget.swipeIntensity;
     final oldDragExtent = _dragExtent;
     switch (widget.direction) {
       case SwipeDirection.none:
@@ -351,7 +378,7 @@ class _SwipeableState extends State<Swipeable> with TickerProviderStateMixin, Au
       return;
     }
     _dragUnderway = false;
-    if (_moveController.isCompleted && await _confirmStartSwipeAnimation() == true) {
+    if (_moveController.value >= widget.maxOffset && await _confirmStartSwipeAnimation() == true) {
       _startSwipeAnimation();
       return;
     }
@@ -375,12 +402,7 @@ class _SwipeableState extends State<Swipeable> with TickerProviderStateMixin, Au
         break;
       case _FlingGestureKind.none:
         if (!_moveController.isDismissed) {
-          // we already know it's not completed, we check that above
-          if (_moveController.value > (widget.dismissThresholds[_swipeDirection] ?? _kDismissThreshold)) {
-            await _moveController.forward();
-          } else {
-            await _moveController.reverse();
-          }
+          await _moveController.reverse();
         }
         break;
     }
@@ -406,7 +428,6 @@ class _SwipeableState extends State<Swipeable> with TickerProviderStateMixin, Au
   }
 
   void _startSwipeAnimation() {
-    assert(_moveController.isCompleted);
     assert(_sizePriorToCollapse == null);
 
     final direction = _swipeDirection;
@@ -428,7 +449,7 @@ class _SwipeableState extends State<Swipeable> with TickerProviderStateMixin, Au
         background = widget.secondaryBackground;
       }
     }
-
+    
     Widget content = SlideTransition(
       position: _moveAnimation,
       child: widget.child,