Surface border parameter in CupertinoSliverNavigationBar (#18194)

* Surface border parameter in CupertinoSliverNavigationBar (#18152)

* Add tests for CupertinoSliverNavigationBar border

* Remove unused keys, find by descendant

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

@@ -195,6 +195,7 @@ class CupertinoSliverNavigationBar extends StatelessWidget {
     this.automaticallyImplyLeading = true,
     this.middle,
     this.trailing,
+    this.border = _kDefaultNavBarBorder,
     this.backgroundColor = _kDefaultNavBarBackgroundColor,
     this.actionsForegroundColor = CupertinoColors.activeBlue,
   }) : assert(largeTitle != null),
@@ -245,6 +246,11 @@ class CupertinoSliverNavigationBar extends StatelessWidget {
   /// This widget is visible in both collapsed and expanded states.
   final Widget trailing;
 
+  /// The border of the navigation bar. By default renders a single pixel bottom border side.
+  ///
+  /// If a border is null, the navigation bar will not display a border.
+  final Border border;
+
   /// The background color of the navigation bar. If it contains transparency, the
   /// tab bar will automatically produce a blurring effect to the content
   /// behind it.
@@ -271,6 +277,7 @@ class CupertinoSliverNavigationBar extends StatelessWidget {
         automaticallyImplyLeading: automaticallyImplyLeading,
         middle: middle,
         trailing: trailing,
+        border: border,
         backgroundColor: backgroundColor,
         actionsForegroundColor: actionsForegroundColor,
       ),
@@ -447,8 +454,8 @@ class _CupertinoLargeTitleNavigationBarSliverDelegate
     this.automaticallyImplyLeading,
     this.middle,
     this.trailing,
-    this.border = _kDefaultNavBarBorder,
-    this.backgroundColor = _kDefaultNavBarBackgroundColor,
+    this.border,
+    this.backgroundColor,
     this.actionsForegroundColor,
   }) : assert(persistentHeight != null);
 
@@ -552,6 +559,7 @@ class _CupertinoLargeTitleNavigationBarSliverDelegate
         || leading != oldDelegate.leading
         || middle != oldDelegate.middle
         || trailing != oldDelegate.trailing
+        || border != oldDelegate.border
         || backgroundColor != oldDelegate.backgroundColor
         || actionsForegroundColor != oldDelegate.actionsForegroundColor;
   }

packages/flutter/test/cupertino/nav_bar_test.dart

@@ -415,7 +415,10 @@ void main() {
       ),
     );
 
-    final DecoratedBox decoratedBox = tester.widgetList(find.byType(DecoratedBox)).elementAt(1);
+    final DecoratedBox decoratedBox = tester.widgetList(find.descendant(
+      of: find.byType(CupertinoNavigationBar),
+      matching: find.byType(DecoratedBox),
+    )).first;
     expect(decoratedBox.decoration.runtimeType, BoxDecoration);
 
     final BoxDecoration decoration = decoratedBox.decoration;
@@ -448,7 +451,10 @@ void main() {
       ),
     );
 
-    final DecoratedBox decoratedBox = tester.widgetList(find.byType(DecoratedBox)).elementAt(1);
+    final DecoratedBox decoratedBox = tester.widgetList(find.descendant(
+      of: find.byType(CupertinoNavigationBar),
+      matching: find.byType(DecoratedBox),
+    )).first;
     expect(decoratedBox.decoration.runtimeType, BoxDecoration);
 
     final BoxDecoration decoration = decoratedBox.decoration;
@@ -477,13 +483,138 @@ void main() {
       ),
     );
 
-    final DecoratedBox decoratedBox = tester.widgetList(find.byType(DecoratedBox)).elementAt(1);
+    final DecoratedBox decoratedBox = tester.widgetList(find.descendant(
+      of: find.byType(CupertinoNavigationBar),
+      matching: find.byType(DecoratedBox),
+    )).first;
     expect(decoratedBox.decoration.runtimeType, BoxDecoration);
 
     final BoxDecoration decoration = decoratedBox.decoration;
     expect(decoration.border, isNull);
   });
 
+  testWidgets(
+      'Border is displayed by default in sliver nav bar',
+      (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new WidgetsApp(
+        color: const Color(0xFFFFFFFF),
+        onGenerateRoute: (RouteSettings settings) {
+          return new CupertinoPageRoute<void>(
+            settings: settings,
+            builder: (BuildContext context) {
+              return new CupertinoPageScaffold(
+                child: new CustomScrollView(
+                  slivers: const <Widget>[
+                    const CupertinoSliverNavigationBar(
+                      largeTitle: const Text('Large Title'),
+                    ),
+                  ],
+                ),
+              );
+            },
+          );
+        },
+      ),
+    );
+
+    final DecoratedBox decoratedBox = tester.widgetList(find.descendant(
+      of: find.byType(CupertinoSliverNavigationBar),
+      matching: find.byType(DecoratedBox),
+    )).first;
+    expect(decoratedBox.decoration.runtimeType, BoxDecoration);
+
+    final BoxDecoration decoration = decoratedBox.decoration;
+    expect(decoration.border, isNotNull);
+
+    final BorderSide bottom = decoration.border.bottom;
+    expect(bottom, isNotNull);
+  });
+
+  testWidgets(
+      'Border is not displayed when null in sliver nav bar',
+      (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new WidgetsApp(
+        color: const Color(0xFFFFFFFF),
+        onGenerateRoute: (RouteSettings settings) {
+          return new CupertinoPageRoute<void>(
+            settings: settings,
+            builder: (BuildContext context) {
+              return new CupertinoPageScaffold(
+                child: new CustomScrollView(
+                  slivers: const <Widget>[
+                    const CupertinoSliverNavigationBar(
+                      largeTitle: const Text('Large Title'),
+                      border: null,
+                    ),
+                  ],
+                ),
+              );
+            },
+          );
+        },
+      ),
+    );
+
+    final DecoratedBox decoratedBox = tester.widgetList(find.descendant(
+      of: find.byType(CupertinoSliverNavigationBar),
+      matching: find.byType(DecoratedBox),
+    )).first;
+    expect(decoratedBox.decoration.runtimeType, BoxDecoration);
+
+    final BoxDecoration decoration = decoratedBox.decoration;
+    expect(decoration.border, isNull);
+  });
+
+  testWidgets(
+      'Border can be overridden in sliver nav bar',
+      (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new WidgetsApp(
+        color: const Color(0xFFFFFFFF),
+        onGenerateRoute: (RouteSettings settings) {
+          return new CupertinoPageRoute<void>(
+            settings: settings,
+            builder: (BuildContext context) {
+              return new CupertinoPageScaffold(
+                child: new CustomScrollView(
+                  slivers: const <Widget>[
+                    const CupertinoSliverNavigationBar(
+                      largeTitle: const Text('Large Title'),
+                      border: const Border(
+                        bottom: const BorderSide(
+                          color: const Color(0xFFAABBCC),
+                          width: 0.0,
+                        ),
+                      ),
+                    ),
+                  ],
+                ),
+              );
+            },
+          );
+        },
+      ),
+    );
+
+    final DecoratedBox decoratedBox = tester.widgetList(find.descendant(
+      of: find.byType(CupertinoSliverNavigationBar),
+      matching: find.byType(DecoratedBox),
+    )).first;
+    expect(decoratedBox.decoration.runtimeType, BoxDecoration);
+
+    final BoxDecoration decoration = decoratedBox.decoration;
+    expect(decoration.border, isNotNull);
+
+    final BorderSide top = decoration.border.top;
+    expect(top, isNotNull);
+    expect(top, BorderSide.none);
+    final BorderSide bottom = decoration.border.bottom;
+    expect(bottom, isNotNull);
+    expect(bottom.color, const Color(0xFFAABBCC));
+  });
+
   testWidgets(
     'Standard title golden',
     (WidgetTester tester) async {