Added customizable padding for the segmented controll (#34555)

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

@@ -11,9 +11,9 @@ import 'package:flutter/widgets.dart';
 
 import 'theme.dart';
 
-// Minimum padding from horizontal edges of segmented control to edges of
+// Minimum padding from edges of the segmented control to edges of
 // encompassing widget.
-const EdgeInsets _kHorizontalItemPadding = EdgeInsets.symmetric(horizontal: 16.0);
+const EdgeInsetsGeometry _kHorizontalItemPadding = EdgeInsets.symmetric(horizontal: 16.0);
 
 // Minimum height of the segmented control.
 const double _kMinSegmentedControlHeight = 28.0;
@@ -87,6 +87,7 @@ class CupertinoSegmentedControl<T> extends StatefulWidget {
     this.selectedColor,
     this.borderColor,
     this.pressedColor,
+    this.padding,
   }) : assert(children != null),
        assert(children.length >= 2),
        assert(onValueChanged != null),
@@ -179,6 +180,11 @@ class CupertinoSegmentedControl<T> extends StatefulWidget {
   /// Defaults to the selectedColor at 20% opacity if null.
   final Color pressedColor;
 
+  /// The CupertinoSegmentedControl will be placed inside this padding
+  ///
+  /// Defaults to EdgeInsets.symmetric(horizontal: 16.0)
+  final EdgeInsetsGeometry padding;
+
   @override
   _SegmentedControlState<T> createState() => _SegmentedControlState<T>();
 }
@@ -407,7 +413,7 @@ class _SegmentedControlState<T> extends State<CupertinoSegmentedControl<T>>
     );
 
     return Padding(
-      padding: _kHorizontalItemPadding.resolve(Directionality.of(context)),
+      padding: widget.padding ?? _kHorizontalItemPadding,
       child: UnconstrainedBox(
         constrainedAxis: Axis.horizontal,
         child: box,

packages/flutter/test/cupertino/segmented_control_test.dart

@@ -117,6 +117,93 @@ void main() {
     }
   });
 
+  testWidgets('Padding works', (WidgetTester tester) async {
+    const Key key = Key('Container');
+
+    final Map<int, Widget> children = <int, Widget>{};
+    children[0] = const SizedBox(
+      height: double.infinity,
+      child: Text('Child 1'),
+    ) ;
+    children[1] = const SizedBox(
+      height: double.infinity,
+      child: Text('Child 2'),
+    ) ;
+
+    Future<void> verifyPadding({ EdgeInsets padding }) async {
+      final EdgeInsets effectivePadding = padding ?? const EdgeInsets.symmetric(horizontal: 16);
+      final Rect segmentedControlRect = tester.getRect(find.byKey(key));
+      expect(
+          tester.getTopLeft(find.byWidget(children[0])),
+          segmentedControlRect.topLeft.translate(
+            effectivePadding.topLeft.dx,
+            effectivePadding.topLeft.dy,
+          )
+      );
+      expect(
+        tester.getBottomLeft(find.byWidget(children[0])),
+        segmentedControlRect.bottomLeft.translate(
+          effectivePadding.bottomLeft.dx,
+          effectivePadding.bottomLeft.dy,
+        ),
+      );
+
+      expect(
+        tester.getTopRight(find.byWidget(children[1])),
+        segmentedControlRect.topRight.translate(
+          effectivePadding.topRight.dx,
+          effectivePadding.topRight.dy,
+        ),
+      );
+      expect(
+        tester.getBottomRight(find.byWidget(children[1])),
+        segmentedControlRect.bottomRight.translate(
+          effectivePadding.bottomRight.dx,
+          effectivePadding.bottomRight.dy,
+        ),
+      );
+    }
+
+    await tester.pumpWidget(
+        boilerplate(
+          child: CupertinoSegmentedControl<int>(
+            key: key,
+            children: children,
+            onValueChanged: (int newValue) { },
+          ),
+        )
+    );
+
+    // Default padding works.
+    await verifyPadding();
+
+    // Switch to Child 2 padding should remain the same.
+    await tester.tap(find.text('Child 2'));
+    await tester.pumpAndSettle();
+
+    await verifyPadding();
+
+    await tester.pumpWidget(
+        boilerplate(
+          child: CupertinoSegmentedControl<int>(
+            key: key,
+            padding: const EdgeInsets.fromLTRB(1, 3, 5, 7),
+            children: children,
+            onValueChanged: (int newValue) { },
+          ),
+        )
+    );
+
+    // Custom padding works.
+    await verifyPadding(padding: const EdgeInsets.fromLTRB(1, 3, 5, 7));
+
+    // Switch back to Child 1 padding should remain the same.
+    await tester.tap(find.text('Child 1'));
+    await tester.pumpAndSettle();
+
+    await verifyPadding(padding: const EdgeInsets.fromLTRB(1, 3, 5, 7));
+  });
+
   testWidgets('Value attribute must be the key of one of the children widgets', (WidgetTester tester) async {
     final Map<int, Widget> children = <int, Widget>{};
     children[0] = const Text('Child 1');