Add `brightness` to CupertinoNavigationBar (fixes #46216) (#47521)

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

@@ -87,15 +87,24 @@ class _HeroTag {
 Widget _wrapWithBackground({
   Border border,
   Color backgroundColor,
+  Brightness brightness,
   Widget child,
   bool updateSystemUiOverlay = true,
 }) {
   Widget result = child;
   if (updateSystemUiOverlay) {
-    final bool darkBackground = backgroundColor.computeLuminance() < 0.179;
-    final SystemUiOverlayStyle overlayStyle = darkBackground
-        ? SystemUiOverlayStyle.light
-        : SystemUiOverlayStyle.dark;
+    final bool isDark = backgroundColor.computeLuminance() < 0.179;
+    final Brightness newBrightness = brightness ?? (isDark ? Brightness.dark : Brightness.light);
+    SystemUiOverlayStyle overlayStyle;
+    switch (newBrightness) {
+      case Brightness.dark:
+        overlayStyle = SystemUiOverlayStyle.light;
+        break;
+      case Brightness.light:
+      default:
+        overlayStyle = SystemUiOverlayStyle.dark;
+        break;
+    }
     result = AnnotatedRegion<SystemUiOverlayStyle>(
       value: overlayStyle,
       sized: true,
@@ -206,6 +215,7 @@ class CupertinoNavigationBar extends StatefulWidget implements ObstructingPrefer
     this.trailing,
     this.border = _kDefaultNavBarBorder,
     this.backgroundColor,
+    this.brightness,
     this.padding,
     this.actionsForegroundColor,
     this.transitionBetweenRoutes = true,
@@ -301,6 +311,18 @@ class CupertinoNavigationBar extends StatefulWidget implements ObstructingPrefer
   /// {@endtemplate}
   final Color backgroundColor;
 
+  /// {@template flutter.cupertino.navBar.brightness}
+  /// The brightness of the specified [backgroundColor].
+  ///
+  /// Setting this value changes the style of the system status bar. Typically
+  /// used to increase the contrast ratio of the system status bar over
+  /// [backgroundColor].
+  ///
+  /// If set to null, the value of the property will be inferred from the relative
+  /// luminance of [backgroundColor].
+  /// {@endtemplate}
+  final Brightness brightness;
+
   /// {@template flutter.cupertino.navBar.padding}
   /// Padding for the contents of the navigation bar.
   ///
@@ -427,6 +449,7 @@ class _CupertinoNavigationBarState extends State<CupertinoNavigationBar> {
     final Widget navBar = _wrapWithBackground(
       border: widget.border,
       backgroundColor: backgroundColor,
+      brightness: widget.brightness,
       child: DefaultTextStyle(
         style: CupertinoTheme.of(context).textTheme.textStyle,
         child: _PersistentNavigationBar(
@@ -547,6 +570,7 @@ class CupertinoSliverNavigationBar extends StatefulWidget {
     this.trailing,
     this.border = _kDefaultNavBarBorder,
     this.backgroundColor,
+    this.brightness,
     this.padding,
     this.actionsForegroundColor,
     this.transitionBetweenRoutes = true,
@@ -620,6 +644,9 @@ class CupertinoSliverNavigationBar extends StatefulWidget {
   /// {@macro flutter.cupertino.navBar.backgroundColor}
   final Color backgroundColor;
 
+  /// {@macro flutter.cupertino.navBar.brightness}
+  final Brightness brightness;
+
   /// {@macro flutter.cupertino.navBar.padding}
   final EdgeInsetsDirectional padding;
 
@@ -694,6 +721,7 @@ class _CupertinoSliverNavigationBarState extends State<CupertinoSliverNavigation
             components: components,
             userMiddle: widget.middle,
             backgroundColor: CupertinoDynamicColor.resolve(widget.backgroundColor, context) ?? CupertinoTheme.of(context).barBackgroundColor,
+            brightness: widget.brightness,
             border: widget.border,
             padding: widget.padding,
             actionsForegroundColor: actionsForegroundColor,
@@ -715,6 +743,7 @@ class _LargeTitleNavigationBarSliverDelegate
     @required this.components,
     @required this.userMiddle,
     @required this.backgroundColor,
+    @required this.brightness,
     @required this.border,
     @required this.padding,
     @required this.actionsForegroundColor,
@@ -730,6 +759,7 @@ class _LargeTitleNavigationBarSliverDelegate
   final _NavigationBarStaticComponents components;
   final Widget userMiddle;
   final Color backgroundColor;
+  final Brightness brightness;
   final Border border;
   final EdgeInsetsDirectional padding;
   final Color actionsForegroundColor;
@@ -760,6 +790,7 @@ class _LargeTitleNavigationBarSliverDelegate
     final Widget navBar = _wrapWithBackground(
       border: border,
       backgroundColor: CupertinoDynamicColor.resolve(backgroundColor, context),
+      brightness: brightness,
       child: DefaultTextStyle(
         style: CupertinoTheme.of(context).textTheme.textStyle,
         child: Stack(

packages/flutter/test/cupertino/nav_bar_test.dart

@@ -136,6 +136,70 @@ void main() {
     expect(tester.getCenter(find.text('Title')).dx, 400.0);
   });
 
+  testWidgets('Can specify custom brightness', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const CupertinoApp(
+        home: CupertinoNavigationBar(
+          backgroundColor: Color(0xF0F9F9F9),
+          brightness: Brightness.dark,
+        ),
+      ),
+    );
+
+    final AnnotatedRegion<SystemUiOverlayStyle> region1 = tester.allWidgets.singleWhere((
+        Widget widget) => widget is AnnotatedRegion);
+    expect(region1.value, SystemUiOverlayStyle.light);
+
+    await tester.pumpWidget(
+      const CupertinoApp(
+        home: CupertinoNavigationBar(
+          backgroundColor: Color(0xF01D1D1D),
+          brightness: Brightness.light,
+        ),
+      ),
+    );
+
+    final AnnotatedRegion<SystemUiOverlayStyle> region2 = tester.allWidgets.singleWhere((
+        Widget widget) => widget is AnnotatedRegion);
+    expect(region2.value, SystemUiOverlayStyle.dark);
+
+    await tester.pumpWidget(
+      const CupertinoApp(
+        home: CustomScrollView(
+          slivers: <Widget>[
+            CupertinoSliverNavigationBar(
+              largeTitle: Text('Title'),
+              backgroundColor: Color(0xF0F9F9F9),
+              brightness: Brightness.dark,
+            )
+          ],
+        ),
+      ),
+    );
+
+    final AnnotatedRegion<SystemUiOverlayStyle> region3 = tester.allWidgets.singleWhere((
+        Widget widget) => widget is AnnotatedRegion);
+    expect(region3.value, SystemUiOverlayStyle.light);
+
+    await tester.pumpWidget(
+      const CupertinoApp(
+        home: CustomScrollView(
+          slivers: <Widget>[
+            CupertinoSliverNavigationBar(
+              largeTitle: Text('Title'),
+              backgroundColor: Color(0xF01D1D1D),
+              brightness: Brightness.light,
+            )
+          ],
+        ),
+      ),
+    );
+
+    final AnnotatedRegion<SystemUiOverlayStyle> region4 = tester.allWidgets.singleWhere((
+        Widget widget) => widget is AnnotatedRegion);
+    expect(region4.value, SystemUiOverlayStyle.dark);
+  });
+
   testWidgets('Padding works in RTL', (WidgetTester tester) async {
     await tester.pumpWidget(
       const CupertinoApp(