fix(ios): learn detent offset before present transition emits positions

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### 🐛 Bug fixes
+
+- **iOS**: `onPositionChange` no longer emits a slightly fractional `index` during the present transition — the detent offset is now learned before positions are emitted, so the index lands exactly on the target detent instead of snapping after `didPresent`. ([#731](https://github.com/lodev09/react-native-true-sheet/pull/731) by [@lodev09](https://github.com/lodev09))
+
 ## 3.11.5
 
 ### 🎉 New features

example/bare/ios/Podfile.lock

@@ -2049,7 +2049,7 @@ PODS:
     - ReactCommon/turbomodule/core
     - ReactNativeDependencies
     - Yoga
-  - RNTrueSheet (3.11.4):
+  - RNTrueSheet (3.11.5):
     - hermes-engine
     - RCTRequired
     - RCTTypeSafety
@@ -2481,7 +2481,7 @@ SPEC CHECKSUMS:
   RNGestureHandler: 2ff61eac036eaf89f6818bf4ed9c39771a17d134
   RNReanimated: f735b1747a7a93bda7ca102c6d37a3cf54b6d5e8
   RNScreens: 991cc417cd396602a6cf59a42139e5a9d91462a9
-  RNTrueSheet: 4dcd3292bcfe21502d48e0fd26b4fb3f68da0ad9
+  RNTrueSheet: 4dfa8b05506db77a67c8a2a54bc563338450408c
   RNWorklets: 4931990f73bc8f347586918b2e13f11dfadf3b75
   Yoga: 77dfa8673de2874e1855002ae59c68b8be9b007b
 

example/shared/src/components/sheets/BasicSheet.tsx

@@ -123,9 +123,9 @@ export const BasicSheet = forwardRef((props: BasicSheetProps, ref: Ref<TrueSheet
       <Button text={`Add Content (${contentCount})`} onPress={addContent} />
       {contentCount > 0 && <Button text="Remove Content" onPress={removeContent} />}
       <ButtonGroup>
+        <Button text="Peek" onPress={() => resize(0)} />
+        <Button text="Auto" onPress={() => resize(1)} />
         <Button text="Large" onPress={() => resize(2)} />
-        <Button text="80%" onPress={() => resize(1)} />
-        <Button text="Auto" onPress={() => resize(0)} />
       </ButtonGroup>
       <TrueSheetPeek />
       <Spacer />

ios/TrueSheetViewController.mm

@@ -261,14 +261,12 @@ - (void)viewDidAppear:(BOOL)animated {
 
     dispatch_async(dispatch_get_main_queue(), ^{
       NSInteger index = [self currentDetentIndex];
-      [self learnOffsetForDetentIndex:index];
-
       CGFloat detent = [self detentValueForIndex:index];
       [self.delegate viewControllerDidPresentAtIndex:index position:self.currentPosition detent:detent];
       [self.delegate viewControllerDidFocus];
 
       [self->_grabberView updateAccessibilityValueWithIndex:index detentCount:self->_detents.count];
-      [self emitChangePositionDelegateWithPosition:self.currentPosition realtime:NO debug:@"did present"];
+      [self settleAtDetentIndex:index debug:@"did present"];
     });
 
     [self setupGestureRecognizer];
@@ -473,18 +471,17 @@ - (void)viewWillLayoutSubviews {
   if (!_isTransitioning && !_isInteractiveDismiss) {
     _isTrackingPositionFromLayout = YES;
 
-    UIViewController *presented = self.presentedViewController;
-    BOOL hasPresentedController = presented != nil && !presented.isBeingPresented && !presented.isBeingDismissed;
-    BOOL realtime = !hasPresentedController;
-
     if (_pendingContentSizeChange || _pendingDetentsChange) {
       _pendingContentSizeChange = NO;
       _pendingDetentsChange = NO;
-      realtime = NO;
-      [self learnOffsetForDetentIndex:self.currentDetentIndex];
+      [self settleAtDetentIndex:self.currentDetentIndex debug:@"layout"];
+    } else {
+      UIViewController *presented = self.presentedViewController;
+      BOOL hasPresentedController = presented != nil && !presented.isBeingPresented && !presented.isBeingDismissed;
+      [self emitChangePositionDelegateWithPosition:self.currentPosition
+                                          realtime:!hasPresentedController
+                                             debug:@"layout"];
     }
-
-    [self emitChangePositionDelegateWithPosition:self.currentPosition realtime:realtime debug:@"layout"];
   }
 }
 
@@ -503,11 +500,10 @@ - (void)viewDidLayoutSubviews {
     _pendingDetentIndex = -1;
 
     dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
-      [self learnOffsetForDetentIndex:pendingIndex];
       CGFloat detent = [self detentValueForIndex:pendingIndex];
       [self.delegate viewControllerDidChangeDetent:pendingIndex position:self.currentPosition detent:detent];
       [self->_grabberView updateAccessibilityValueWithIndex:pendingIndex detentCount:self->_detents.count];
-      [self emitChangePositionDelegateWithPosition:self.currentPosition realtime:NO debug:@"pending detent change"];
+      [self settleAtDetentIndex:pendingIndex debug:@"pending detent change"];
     });
   }
 
@@ -582,9 +578,8 @@ - (void)handlePanGesture:(UIPanGestureRecognizer *)gesture {
       if (!_isTransitioning) {
         dispatch_async(dispatch_get_main_queue(), ^{
           NSInteger index = self.currentDetentIndex;
-          [self learnOffsetForDetentIndex:index];
           [self->_grabberView updateAccessibilityValueWithIndex:index detentCount:self->_detents.count];
-          [self emitChangePositionDelegateWithPosition:self.currentPosition realtime:NO debug:@"drag end"];
+          [self settleAtDetentIndex:index debug:@"drag end"];
         });
       }
 
@@ -602,6 +597,13 @@ - (void)setupTransitionTracker {
 
   _isTransitioning = YES;
 
+  // Learn the resolver-vs-actual offset before emitting transition positions so
+  // the interpolated index lands exactly on the target detent. The presented
+  // frame is already final here (UIKit animates the layer, not the frame).
+  if (!self.isBeingDismissed) {
+    [self learnOffsetForDetentIndex:self.currentDetentIndex];
+  }
+
   CGRect dismissedFrame = CGRectMake(0, self.screenHeight, 0, 0);
   CGRect presentedFrame = CGRectMake(0, self.currentPosition, 0, 0);
 
@@ -810,6 +812,16 @@ - (void)learnOffsetForDetentIndex:(NSInteger)index {
   [_detentCalculator learnOffsetForDetentIndex:index];
 }
 
+/**
+ * Learn the resolver-vs-actual offset at a settled detent, then emit the corrected
+ * position. Only valid when presentedView's frame is final — never mid-drag or
+ * mid-animation, where learning would store a bogus offset.
+ */
+- (void)settleAtDetentIndex:(NSInteger)index debug:(NSString *)debug {
+  [self learnOffsetForDetentIndex:index];
+  [self emitChangePositionDelegateWithPosition:self.currentPosition realtime:NO debug:debug];
+}
+
 - (BOOL)findSegmentForPosition:(CGFloat)position outIndex:(NSInteger *)outIndex outProgress:(CGFloat *)outProgress {
   return [_detentCalculator findSegmentForPosition:position outIndex:outIndex outProgress:outProgress];
 }