fix: bottom navigation bar colors (#107924)

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

@@ -154,6 +154,11 @@ class BottomNavigationBar extends StatefulWidget {
   /// [selectedIconTheme] and [unselectedIconTheme], and both
   /// [IconThemeData.color] and [IconThemeData.size] must be set.
   ///
+  /// If [useLegacyColorScheme] is set to `false`
+  /// [selectedIconTheme] values will be used instead of [iconSize] and [selectedItemColor] for selected icons.
+  /// [unselectedIconTheme] values will be used instead of [iconSize] and [unselectedItemColor] for unselected icons.
+  ///
+  ///
   /// If both [selectedLabelStyle].fontSize and [selectedFontSize] are set,
   /// [selectedLabelStyle].fontSize will be used.
   ///
@@ -193,6 +198,7 @@ class BottomNavigationBar extends StatefulWidget {
     this.mouseCursor,
     this.enableFeedback,
     this.landscapeLayout,
+    this.useLegacyColorScheme = true,
   }) : assert(items != null),
        assert(items.length >= 2),
        assert(
@@ -381,6 +387,13 @@ class BottomNavigationBar extends StatefulWidget {
   ///    orientation.
   final BottomNavigationBarLandscapeLayout? landscapeLayout;
 
+  /// This flag is controlling how [BottomNavigationBar] is going to use
+  /// the colors provided by the [selectedIconTheme], [unselectedIconTheme],
+  /// [selectedItemColor], [unselectedItemColor].
+  /// The default value is `true` as the new theming logic is a breaking change.
+  /// To opt-in the new theming logic set the flag to `false`
+  final bool useLegacyColorScheme;
+
   @override
   State<BottomNavigationBar> createState() => _BottomNavigationBarState();
 }
@@ -394,7 +407,8 @@ class _BottomNavigationTile extends StatelessWidget {
     this.animation,
     this.iconSize, {
     this.onTap,
-    this.colorTween,
+    this.labelColorTween,
+    this.iconColorTween,
     this.flex,
     this.selected = false,
     required this.selectedLabelStyle,
@@ -420,7 +434,8 @@ class _BottomNavigationTile extends StatelessWidget {
   final Animation<double> animation;
   final double iconSize;
   final VoidCallback? onTap;
-  final ColorTween? colorTween;
+  final ColorTween? labelColorTween;
+  final ColorTween? iconColorTween;
   final double? flex;
   final bool selected;
   final IconThemeData? selectedIconTheme;
@@ -523,7 +538,7 @@ class _BottomNavigationTile extends StatelessWidget {
         child: _Tile(
           layout: layout,
           icon: _TileIcon(
-            colorTween: colorTween!,
+            colorTween: iconColorTween!,
             animation: animation,
             iconSize: iconSize,
             selected: selected,
@@ -532,7 +547,7 @@ class _BottomNavigationTile extends StatelessWidget {
             unselectedIconTheme: unselectedIconTheme,
           ),
           label: _Label(
-            colorTween: colorTween!,
+            colorTween: labelColorTween!,
             animation: animation,
             item: item,
             selectedLabelStyle: selectedLabelStyle,
@@ -910,6 +925,15 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
     return textStyle.fontSize == null ? textStyle.copyWith(fontSize: fontSize) : textStyle;
   }
 
+  // If [IconThemeData] is provided, it should be used.
+  // Otherwise, the [IconThemeData]'s color should be selectedItemColor
+  // or unselectedItemColor.
+  static IconThemeData _effectiveIconTheme(IconThemeData? iconTheme, Color? itemColor) {
+    // Prefer the iconTheme over itemColor if present.
+    return iconTheme ?? IconThemeData(color: itemColor);
+  }
+
+
   List<Widget> _createTiles(BottomNavigationBarLandscapeLayout layout) {
     final MaterialLocalizations localizations = MaterialLocalizations.of(context);
     assert(localizations != null);
@@ -917,17 +941,6 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
     final ThemeData themeData = Theme.of(context);
     final BottomNavigationBarThemeData bottomTheme = BottomNavigationBarTheme.of(context);
 
-    final TextStyle effectiveSelectedLabelStyle =
-      _effectiveTextStyle(
-        widget.selectedLabelStyle ?? bottomTheme.selectedLabelStyle,
-        widget.selectedFontSize,
-      );
-    final TextStyle effectiveUnselectedLabelStyle =
-      _effectiveTextStyle(
-        widget.unselectedLabelStyle ?? bottomTheme.unselectedLabelStyle,
-        widget.unselectedFontSize,
-      );
-
     final Color themeColor;
     switch (themeData.brightness) {
       case Brightness.light:
@@ -938,6 +951,39 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
         break;
     }
 
+    final TextStyle effectiveSelectedLabelStyle =
+      _effectiveTextStyle(
+        widget.selectedLabelStyle
+        ?? bottomTheme.selectedLabelStyle,
+        widget.selectedFontSize,
+      );
+
+    final TextStyle effectiveUnselectedLabelStyle =
+      _effectiveTextStyle(
+        widget.unselectedLabelStyle
+        ?? bottomTheme.unselectedLabelStyle,
+        widget.unselectedFontSize,
+      );
+
+    final IconThemeData effectiveSelectedIconTheme =
+      _effectiveIconTheme(
+        widget.selectedIconTheme
+        ?? bottomTheme.selectedIconTheme,
+        widget.selectedItemColor
+        ?? bottomTheme.selectedItemColor
+        ?? themeColor
+      );
+
+    final IconThemeData effectiveUnselectedIconTheme =
+      _effectiveIconTheme(
+        widget.unselectedIconTheme
+        ?? bottomTheme.unselectedIconTheme,
+        widget.unselectedItemColor
+        ?? bottomTheme.unselectedItemColor
+        ?? themeData.unselectedWidgetColor
+      );
+
+
     final ColorTween colorTween;
     switch (_effectiveType) {
       case BottomNavigationBarType.fixed:
@@ -963,6 +1009,64 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
         break;
     }
 
+    final ColorTween labelColorTween;
+    switch (_effectiveType) {
+      case BottomNavigationBarType.fixed:
+        labelColorTween = ColorTween(
+          begin: effectiveUnselectedLabelStyle.color
+            ?? widget.unselectedItemColor
+            ?? bottomTheme.unselectedItemColor
+            ?? themeData.unselectedWidgetColor,
+          end: effectiveSelectedLabelStyle.color
+            ?? widget.selectedItemColor
+            ?? bottomTheme.selectedItemColor
+            ?? widget.fixedColor
+            ?? themeColor,
+        );
+        break;
+      case BottomNavigationBarType.shifting:
+        labelColorTween = ColorTween(
+          begin: effectiveUnselectedLabelStyle.color
+            ?? widget.unselectedItemColor
+            ?? bottomTheme.unselectedItemColor
+            ?? themeData.colorScheme.surface,
+          end: effectiveSelectedLabelStyle.color
+            ?? widget.selectedItemColor
+            ?? bottomTheme.selectedItemColor
+            ?? themeColor,
+        );
+        break;
+    }
+
+    final ColorTween iconColorTween;
+    switch (_effectiveType) {
+      case BottomNavigationBarType.fixed:
+        iconColorTween = ColorTween(
+          begin: effectiveSelectedIconTheme.color
+            ?? widget.unselectedItemColor
+            ?? bottomTheme.unselectedItemColor
+            ?? themeData.unselectedWidgetColor,
+          end: effectiveUnselectedIconTheme.color
+            ?? widget.selectedItemColor
+            ?? bottomTheme.selectedItemColor
+            ?? widget.fixedColor
+            ?? themeColor,
+        );
+        break;
+      case BottomNavigationBarType.shifting:
+        iconColorTween = ColorTween(
+          begin: effectiveUnselectedIconTheme.color
+            ?? widget.unselectedItemColor
+            ?? bottomTheme.unselectedItemColor
+            ?? themeData.colorScheme.surface,
+          end: effectiveSelectedIconTheme.color
+            ?? widget.selectedItemColor
+            ?? bottomTheme.selectedItemColor
+            ?? themeColor,
+        );
+        break;
+    }
+
     final List<Widget> tiles = <Widget>[];
     for (int i = 0; i < widget.items.length; i++) {
       final Set<MaterialState> states = <MaterialState>{
@@ -978,15 +1082,16 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
         widget.items[i],
         _animations[i],
         widget.iconSize,
-        selectedIconTheme: widget.selectedIconTheme ?? bottomTheme.selectedIconTheme,
-        unselectedIconTheme: widget.unselectedIconTheme ?? bottomTheme.unselectedIconTheme,
+        selectedIconTheme: widget.useLegacyColorScheme ? widget.selectedIconTheme ?? bottomTheme.selectedIconTheme : effectiveSelectedIconTheme,
+        unselectedIconTheme: widget.useLegacyColorScheme ? widget.unselectedIconTheme ?? bottomTheme.unselectedIconTheme : effectiveUnselectedIconTheme,
         selectedLabelStyle: effectiveSelectedLabelStyle,
         unselectedLabelStyle: effectiveUnselectedLabelStyle,
         enableFeedback: widget.enableFeedback ?? bottomTheme.enableFeedback ?? true,
         onTap: () {
           widget.onTap?.call(i);
         },
-        colorTween: colorTween,
+        labelColorTween: widget.useLegacyColorScheme ? colorTween : labelColorTween,
+        iconColorTween: widget.useLegacyColorScheme ? colorTween : iconColorTween,
         flex: _evaluateFlex(_animations[i]),
         selected: i == widget.currentIndex,
         showSelectedLabels: widget.showSelectedLabels ?? bottomTheme.showSelectedLabels ?? true,