Add shadowColor to AppBar and AppBarTheme (#58708)

packages/flutter/lib/src/material/app_bar.dart

@@ -175,7 +175,7 @@ class AppBar extends StatefulWidget implements PreferredSizeWidget {
   /// and [automaticallyImplyLeading] must not be null. Additionally, if
   /// [elevation] is specified, it must be non-negative.
   ///
-  /// If [backgroundColor], [elevation], [brightness], [iconTheme],
+  /// If [backgroundColor], [elevation], [shadowColor], [brightness], [iconTheme],
   /// [actionsIconTheme], [textTheme] or [centerTitle] are null, then their
   /// [AppBarTheme] values will be used. If the corresponding [AppBarTheme] property is null,
   /// then the default specified in the property's documentation will be used.
@@ -190,6 +190,7 @@ class AppBar extends StatefulWidget implements PreferredSizeWidget {
     this.flexibleSpace,
     this.bottom,
     this.elevation,
+    this.shadowColor,
     this.shape,
     this.backgroundColor,
     this.brightness,
@@ -338,6 +339,13 @@ class AppBar extends StatefulWidget implements PreferredSizeWidget {
   /// for app bars.
   final double elevation;
 
+  /// The color to paint the shadow below the app bar.
+  ///
+  /// If this property is null, then [ThemeData.appBarTheme.shadowColor] is used,
+  /// if that is also null, the default value is fully opaque black, the appropriate
+  /// color for shadows.
+  final Color shadowColor;
+
   /// The material's shape as well its shadow.
   ///
   /// A shadow is only displayed if the [elevation] is greater than
@@ -456,6 +464,7 @@ class AppBar extends StatefulWidget implements PreferredSizeWidget {
 
 class _AppBarState extends State<AppBar> {
   static const double _defaultElevation = 4.0;
+  static const Color _defaultShadowColor = Color(0xFF000000);
 
   void _handleDrawerButton() {
     Scaffold.of(context).openDrawer();
@@ -665,6 +674,9 @@ class _AppBarState extends State<AppBar> {
           elevation: widget.elevation
             ?? appBarTheme.elevation
             ?? _defaultElevation,
+          shadowColor: widget.shadowColor
+            ?? appBarTheme.shadowColor
+            ?? _defaultShadowColor,
           shape: widget.shape,
           child: Semantics(
             explicitChildNodes: true,
@@ -737,6 +749,7 @@ class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
     @required this.flexibleSpace,
     @required this.bottom,
     @required this.elevation,
+    @required this.shadowColor,
     @required this.forceElevated,
     @required this.backgroundColor,
     @required this.brightness,
@@ -765,6 +778,7 @@ class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
   final Widget flexibleSpace;
   final PreferredSizeWidget bottom;
   final double elevation;
+  final Color shadowColor;
   final bool forceElevated;
   final Color backgroundColor;
   final Brightness brightness;
@@ -822,6 +836,7 @@ class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
           : flexibleSpace,
         bottom: bottom,
         elevation: forceElevated || overlapsContent || (pinned && shrinkOffset > maxExtent - minExtent) ? elevation ?? 4.0 : 0.0,
+        shadowColor: shadowColor,
         backgroundColor: backgroundColor,
         brightness: brightness,
         iconTheme: iconTheme,
@@ -849,6 +864,7 @@ class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
         || bottom != oldDelegate.bottom
         || _bottomHeight != oldDelegate._bottomHeight
         || elevation != oldDelegate.elevation
+        || shadowColor != oldDelegate.shadowColor
         || backgroundColor != oldDelegate.backgroundColor
         || brightness != oldDelegate.brightness
         || iconTheme != oldDelegate.iconTheme
@@ -964,6 +980,7 @@ class SliverAppBar extends StatefulWidget {
     this.flexibleSpace,
     this.bottom,
     this.elevation,
+    this.shadowColor,
     this.forceElevated = false,
     this.backgroundColor,
     this.brightness,
@@ -1081,6 +1098,14 @@ class SliverAppBar extends StatefulWidget {
   /// shadow is drawn, regardless of the value of [elevation].
   final double elevation;
 
+  /// The color to paint the shadow below the app bar. Typically this should be set
+  /// along with [elevation].
+  ///
+  /// If this property is null, then [ThemeData.appBarTheme.shadowColor] is used,
+  /// if that is also null, the default value is fully opaque black, the appropriate
+  /// color for shadows.
+  final Color shadowColor;
+
   /// Whether to show the shadow appropriate for the [elevation] even if the
   /// content is not scrolled under the [AppBar].
   ///
@@ -1339,6 +1364,7 @@ class _SliverAppBarState extends State<SliverAppBar> with TickerProviderStateMix
           flexibleSpace: widget.flexibleSpace,
           bottom: widget.bottom,
           elevation: widget.elevation,
+          shadowColor: widget.shadowColor,
           forceElevated: widget.forceElevated,
           backgroundColor: widget.backgroundColor,
           brightness: widget.brightness,

packages/flutter/lib/src/material/app_bar_theme.dart

@@ -36,6 +36,7 @@ class AppBarTheme with Diagnosticable {
     this.brightness,
     this.color,
     this.elevation,
+    this.shadowColor,
     this.iconTheme,
     this.actionsIconTheme,
     this.textTheme,
@@ -57,6 +58,11 @@ class AppBarTheme with Diagnosticable {
   /// If null, [AppBar] uses a default value of 4.0.
   final double elevation;
 
+  /// Default value for [AppBar.shadowColor].
+  ///
+  /// If null, [AppBar] uses a default value of fully opaque black.
+  final Color shadowColor;
+
   /// Default value for [AppBar.iconTheme].
   ///
   /// If null, [AppBar] uses [ThemeData.primaryIconTheme].
@@ -84,6 +90,7 @@ class AppBarTheme with Diagnosticable {
     Brightness brightness,
     Color color,
     double elevation,
+    Color shadowColor,
     IconThemeData iconTheme,
     TextTheme textTheme,
     bool centerTitle,
@@ -92,6 +99,7 @@ class AppBarTheme with Diagnosticable {
       brightness: brightness ?? this.brightness,
       color: color ?? this.color,
       elevation: elevation ?? this.elevation,
+      shadowColor: shadowColor ?? this.shadowColor,
       iconTheme: iconTheme ?? this.iconTheme,
       actionsIconTheme: actionsIconTheme ?? this.actionsIconTheme,
       textTheme: textTheme ?? this.textTheme,
@@ -115,6 +123,7 @@ class AppBarTheme with Diagnosticable {
       brightness: t < 0.5 ? a?.brightness : b?.brightness,
       color: Color.lerp(a?.color, b?.color, t),
       elevation: lerpDouble(a?.elevation, b?.elevation, t),
+      shadowColor: Color.lerp(a?.shadowColor, b?.shadowColor, t),
       iconTheme: IconThemeData.lerp(a?.iconTheme, b?.iconTheme, t),
       actionsIconTheme: IconThemeData.lerp(a?.actionsIconTheme, b?.actionsIconTheme, t),
       textTheme: TextTheme.lerp(a?.textTheme, b?.textTheme, t),
@@ -128,6 +137,7 @@ class AppBarTheme with Diagnosticable {
       brightness,
       color,
       elevation,
+      shadowColor,
       iconTheme,
       actionsIconTheme,
       textTheme,
@@ -145,6 +155,7 @@ class AppBarTheme with Diagnosticable {
         && other.brightness == brightness
         && other.color == color
         && other.elevation == elevation
+        && other.shadowColor == shadowColor
         && other.iconTheme == iconTheme
         && other.actionsIconTheme == actionsIconTheme
         && other.textTheme == textTheme
@@ -157,6 +168,7 @@ class AppBarTheme with Diagnosticable {
     properties.add(DiagnosticsProperty<Brightness>('brightness', brightness, defaultValue: null));
     properties.add(ColorProperty('color', color, defaultValue: null));
     properties.add(DiagnosticsProperty<double>('elevation', elevation, defaultValue: null));
+    properties.add(ColorProperty('shadowColor', shadowColor, defaultValue: null));
     properties.add(DiagnosticsProperty<IconThemeData>('iconTheme', iconTheme, defaultValue: null));
     properties.add(DiagnosticsProperty<IconThemeData>('actionsIconTheme', actionsIconTheme, defaultValue: null));
     properties.add(DiagnosticsProperty<TextTheme>('textTheme', textTheme, defaultValue: null));

packages/flutter/test/material/app_bar_theme_test.dart

@@ -33,6 +33,7 @@ void main() {
     expect(SystemChrome.latestStyle.statusBarBrightness, Brightness.dark);
     expect(widget.color, Colors.blue);
     expect(widget.elevation, 4.0);
+    expect(widget.shadowColor, Colors.black);
     expect(iconTheme.data, const IconThemeData(color: Colors.white));
     expect(actionsIconTheme.data, const IconThemeData(color: Colors.white));
     expect(actionIconText.text.style.color, Colors.white);
@@ -61,6 +62,7 @@ void main() {
     expect(SystemChrome.latestStyle.statusBarBrightness, appBarTheme.brightness);
     expect(widget.color, appBarTheme.color);
     expect(widget.elevation, appBarTheme.elevation);
+    expect(widget.shadowColor, appBarTheme.shadowColor);
     expect(iconTheme.data, appBarTheme.iconTheme);
     expect(actionsIconTheme.data, appBarTheme.actionsIconTheme);
     expect(actionIconText.text.style.color, appBarTheme.actionsIconTheme.color);
@@ -71,6 +73,7 @@ void main() {
     const Brightness brightness = Brightness.dark;
     const Color color = Colors.orange;
     const double elevation = 3.0;
+    const Color shadowColor = Colors.red;
     const IconThemeData iconThemeData = IconThemeData(color: Colors.green);
     const IconThemeData actionsIconThemeData = IconThemeData(color: Colors.lightBlue);
     const TextTheme textTheme = TextTheme(headline6: TextStyle(color: Colors.orange), bodyText2: TextStyle(color: Colors.pink));
@@ -83,6 +86,7 @@ void main() {
         backgroundColor: color,
         brightness: brightness,
         elevation: elevation,
+        shadowColor: shadowColor,
         iconTheme: iconThemeData,
         actionsIconTheme: actionsIconThemeData,
         textTheme: textTheme,
@@ -101,6 +105,7 @@ void main() {
     expect(SystemChrome.latestStyle.statusBarBrightness, brightness);
     expect(widget.color, color);
     expect(widget.elevation, elevation);
+    expect(widget.shadowColor, shadowColor);
     expect(iconTheme.data, iconThemeData);
     expect(actionsIconTheme.data, actionsIconThemeData);
     expect(actionIconText.text.style.color, actionsIconThemeData.color);
@@ -151,6 +156,7 @@ void main() {
     expect(SystemChrome.latestStyle.statusBarBrightness, appBarTheme.brightness);
     expect(widget.color, appBarTheme.color);
     expect(widget.elevation, appBarTheme.elevation);
+    expect(widget.shadowColor, appBarTheme.shadowColor);
     expect(iconTheme.data, appBarTheme.iconTheme);
     expect(actionsIconTheme.data, appBarTheme.actionsIconTheme);
     expect(actionIconText.text.style.color, appBarTheme.actionsIconTheme.color);
@@ -178,6 +184,7 @@ void main() {
     expect(SystemChrome.latestStyle.statusBarBrightness, themeData.brightness);
     expect(widget.color, themeData.primaryColor);
     expect(widget.elevation, 4.0);
+    expect(widget.shadowColor, Colors.black);
     expect(iconTheme.data, themeData.primaryIconTheme);
     expect(actionsIconTheme.data, themeData.primaryIconTheme);
     expect(actionIconText.text.style.color, themeData.primaryIconTheme.color);
@@ -199,10 +206,11 @@ void main() {
     await tester.pumpWidget(MaterialApp(
       theme: ThemeData(appBarTheme: const AppBarTheme(centerTitle: true)),
       home: Scaffold(
-          appBar: AppBar(
-            title: const Text('Title'),
-            centerTitle: false,
-          )),
+        appBar: AppBar(
+          title: const Text('Title'),
+          centerTitle: false,
+        ),
+      ),
     ));
 
     final NavigationToolbar navToolBar = tester.widget(find.byType(NavigationToolbar));
@@ -221,12 +229,29 @@ void main() {
     // the value of NavigationToolBar.centerMiddle should be true.
     expect(navToolBar.centerMiddle, true);
   });
+
+  testWidgets('AppBar.shadowColor takes priority over AppBarTheme.shadowColor', (WidgetTester tester) async {
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData(appBarTheme: const AppBarTheme(shadowColor: Colors.red)),
+      home: Scaffold(
+        appBar: AppBar(
+          title: const Text('Title'),
+          shadowColor: Colors.yellow,
+        ),
+      ),
+    ));
+
+    final AppBar appBar = tester.widget(find.byType(AppBar));
+    // The AppBar.shadowColor should be used instead of AppBarTheme.shadowColor.
+    expect(appBar.shadowColor, Colors.yellow);
+  });
 }
 
 AppBarTheme _appBarTheme() {
   const Brightness brightness = Brightness.light;
   const Color color = Colors.lightBlue;
   const double elevation = 6.0;
+  const Color shadowColor = Colors.red;
   const IconThemeData iconThemeData = IconThemeData(color: Colors.black);
   const IconThemeData actionsIconThemeData = IconThemeData(color: Colors.pink);
   const TextTheme textTheme = TextTheme(bodyText2: TextStyle(color: Colors.yellow));
@@ -235,6 +260,7 @@ AppBarTheme _appBarTheme() {
     brightness: brightness,
     color: color,
     elevation: elevation,
+    shadowColor: shadowColor,
     iconTheme: iconThemeData,
     textTheme: textTheme,
   );
@@ -284,6 +310,7 @@ RichText _getAppBarIconRichText(WidgetTester tester) {
     ).first,
   );
 }
+
 DefaultTextStyle _getAppBarText(WidgetTester tester) {
   return tester.widget<DefaultTextStyle>(
     find.descendant(