[Tabs] Fix tab indicator flies off issue

nero-angela · Nov 13, 2020 · 38f2bc0 · 38f2bc0
1 parent 7cda686
commit 38f2bc0
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Showing 2 changed files with 9 additions and 1 deletion.
diff --git a/packages/flutter/lib/src/material/tab_controller.dart b/packages/flutter/lib/src/material/tab_controller.dart
@@ -224,6 +224,7 @@ class TabController extends ChangeNotifier {
         .whenCompleteOrCancel(() {
           if (_animationController != null) { // don't notify if we've been disposed
             _indexIsChangingCount -= 1;
+            _indexPositionWhenTapping = _animationController!.value;
             notifyListeners();
           }
         });
@@ -235,6 +236,13 @@ class TabController extends ChangeNotifier {
     }
   }
 
+  /// the value of animation controller at the moment of tapping a tab
+  ///
+  /// This value is needed to calculate the position of the indicator
+  /// when selecting a tab during animation.
+  double get indexPositionWhenTapping => _indexPositionWhenTapping ?? _previousIndex.toDouble();
+  double? _indexPositionWhenTapping;
+
   /// The index of the currently selected tab.
   ///
   /// Changing the index also updates [previousIndex], sets the [animation]'s

diff --git a/packages/flutter/lib/src/material/tabs.dart b/packages/flutter/lib/src/material/tabs.dart
@@ -302,7 +302,7 @@ class _TabLabelBar extends Flex {
 
 double _indexChangeProgress(TabController controller) {
   final double controllerValue = controller.animation!.value;
-  final double previousIndex = controller.previousIndex.toDouble();
+  final double previousIndex = controller.indexPositionWhenTapping;
   final double currentIndex = controller.index.toDouble();
 
   // The controller's offset is changing because the user is dragging the