Segmented control quick double tap fix (#44391)

packages/flutter/lib/src/cupertino/nav_bar.dart

@@ -289,7 +289,8 @@ class CupertinoNavigationBar extends StatefulWidget implements ObstructingPrefer
   /// {@endtemplate}
   final Widget trailing;
 
-  // TODO(xster): implement support for double row navigation bars.
+  // TODO(xster): https://github.com/flutter/flutter/issues/10469 implement
+  // support for double row navigation bars.
 
   /// {@template flutter.cupertino.navBar.backgroundColor}
   /// The background color of the navigation bar. If it contains transparency, the

packages/flutter/lib/src/cupertino/segmented_control.dart

@@ -331,10 +331,12 @@ class _SegmentedControlState<T> extends State<CupertinoSegmentedControl<T>>
   }
 
   void _onTap(T currentKey) {
-    if (currentKey != widget.groupValue && currentKey == _pressedKey) {
+    if (currentKey != _pressedKey)
+      return;
+    if (currentKey != widget.groupValue) {
       widget.onValueChanged(currentKey);
-      _pressedKey = null;
     }
+    _pressedKey = null;
   }
 
   Color getTextColor(int index, T currentKey) {
@@ -472,7 +474,6 @@ class _RenderSegmentedControl<T> extends RenderBox
     with ContainerRenderObjectMixin<RenderBox, ContainerBoxParentData<RenderBox>>,
         RenderBoxContainerDefaultsMixin<RenderBox, ContainerBoxParentData<RenderBox>> {
   _RenderSegmentedControl({
-    List<RenderBox> children,
     @required int selectedIndex,
     @required int pressedIndex,
     @required TextDirection textDirection,
@@ -483,9 +484,7 @@ class _RenderSegmentedControl<T> extends RenderBox
        _selectedIndex = selectedIndex,
        _pressedIndex = pressedIndex,
        _backgroundColors = backgroundColors,
-       _borderColor = borderColor {
-    addAll(children);
-  }
+       _borderColor = borderColor;
 
   int get selectedIndex => _selectedIndex;
   int _selectedIndex;

packages/flutter/test/cupertino/segmented_control_test.dart

@@ -1384,6 +1384,47 @@ void main() {
     expect(getBackgroundColor(tester, 1), isSameColorAs(CupertinoColors.white));
   });
 
+  // Regression test: https://github.com/flutter/flutter/issues/43414.
+  testWidgets("Quick double tap doesn't break the internal state", (WidgetTester tester) async {
+    const Map<int, Widget> children = <int, Widget>{
+      0: Text('A'),
+      1: Text('B'),
+      2: Text('C'),
+    };
+    int sharedValue = 0;
+
+    await tester.pumpWidget(
+      StatefulBuilder(
+        builder: (BuildContext context, StateSetter setState) {
+          return boilerplate(
+            child: CupertinoSegmentedControl<int>(
+              key: const ValueKey<String>('Segmented Control'),
+              children: children,
+              onValueChanged: (int newValue) {
+                setState(() { sharedValue = newValue; });
+              },
+              groupValue: sharedValue,
+            ),
+          );
+        },
+      ),
+    );
+
+    await tester.tap(find.text('B'));
+    // sharedValue has been updated but widget.groupValue is not.
+    expect(sharedValue, 1);
+
+    // Land the second tap before the widget gets a chance to rebuild.
+    final TestGesture secondTap = await tester.startGesture(tester.getCenter(find.text('B')));
+    await tester.pump();
+
+    await secondTap.up();
+    expect(sharedValue, 1);
+
+    await tester.tap(find.text('C'));
+    expect(sharedValue, 2);
+  });
+
   testWidgets('Golden Test Placeholder Widget', (WidgetTester tester) async {
     final Map<int, Widget> children = <int, Widget>{};
     children[0] = Container();