BottomNavigationBar accepts widget icons (#7161)

examples/flutter_gallery/lib/demo/bottom_navigation_demo.dart

@@ -6,7 +6,7 @@ import 'package:flutter/material.dart';
 
 class NavigationIconView {
   NavigationIconView({
-    Icon icon,
+    Widget icon,
     Widget title,
     Color color,
     TickerProvider vsync,
@@ -27,7 +27,7 @@ class NavigationIconView {
     );
   }
 
-  final Icon _icon;
+  final Widget _icon;
   final Color _color;
   final DestinationLabel destinationLabel;
   final AnimationController controller;
@@ -51,7 +51,28 @@ class NavigationIconView {
           begin: const FractionalOffset(0.0, 0.02), // Small offset from the top.
           end: FractionalOffset.topLeft,
         ).animate(_animation),
-        child: new Icon(_icon.icon, color: iconColor, size: 120.0),
+        child: new IconTheme(
+          data: new IconThemeData(
+            color: iconColor,
+            size: 120.0,
+          ),
+          child: _icon,
+        ),
+      ),
+    );
+  }
+}
+
+class CustomIcon extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    final IconThemeData iconTheme = IconTheme.of(context).fallback();
+    return new Container(
+      margin: const EdgeInsets.all(4.0),
+      width: iconTheme.size - 8.0,
+      height: iconTheme.size - 8.0,
+      decoration: new BoxDecoration(
+        backgroundColor: iconTheme.color,
       ),
     );
   }
@@ -80,6 +101,12 @@ class _BottomNavigationDemoState extends State<BottomNavigationDemo>
         color: Colors.deepPurple[500],
         vsync: this,
       ),
+      new NavigationIconView(
+        icon: new CustomIcon(),
+        title: new Text('Box'),
+        color: Colors.deepOrange[500],
+        vsync: this,
+      ),
       new NavigationIconView(
         icon: new Icon(Icons.cloud),
         title: new Text('Cloud'),

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

@@ -11,7 +11,6 @@ import 'package:vector_math/vector_math_64.dart' show Vector3;
 
 import 'colors.dart';
 import 'constants.dart';
-import 'icon.dart';
 import 'icon_theme.dart';
 import 'icon_theme_data.dart';
 import 'ink_well.dart';
@@ -59,7 +58,11 @@ class DestinationLabel {
   }
 
   /// The icon of the label.
-  final Icon icon;
+  ///
+  /// Typically the icon is an [Icon] or an [IconImage] widget. If another type
+  /// of widget is provided then it should configure itself to match the current
+  /// [IconTheme] size and color.
+  final Widget icon;
 
   /// The title of the label.
   final Widget title;
@@ -104,15 +107,15 @@ class BottomNavigationBar extends StatefulWidget {
     this.onTap,
     this.currentIndex: 0,
     this.type: BottomNavigationBarType.fixed,
-    this.fixedColor
+    this.fixedColor,
+    this.iconSize: 24.0,
   }) : super(key: key) {
-    assert(this.labels != null);
-    assert(this.labels.length >= 2);
-    assert(0 <= currentIndex && currentIndex < this.labels.length);
-    assert(this.type != null);
-    assert(
-      this.type == BottomNavigationBarType.fixed || this.fixedColor == null
-    );
+    assert(labels != null);
+    assert(labels.length >= 2);
+    assert(0 <= currentIndex && currentIndex < labels.length);
+    assert(type != null);
+    assert(type == BottomNavigationBarType.fixed || fixedColor == null);
+    assert(iconSize != null);
   }
 
   /// The interactive labels laid out within the bottom navigation bar.
@@ -135,6 +138,13 @@ class BottomNavigationBar extends StatefulWidget {
   /// [BottomNavigationBarType.fixed].
   final Color fixedColor;
 
+  /// The size of all of the [DestinationLabel] icons.
+  ///
+  /// This value is used to to configure the [IconTheme] for the navigation
+  /// bar. When a [DestinationLabel.icon] widget is not an [Icon] the widget
+  /// should configure itself to match the icon theme's size and color.
+  final double iconSize;
+
   @override
   BottomNavigationBarState createState() => new BottomNavigationBarState();
 }
@@ -251,8 +261,8 @@ class BottomNavigationBarState extends State<BottomNavigationBar> with TickerPro
     return (leftWeights + _flex(animations[index]) / 2.0) / allWeights;
   }
 
-  FractionalOffset cirleOffset(int index) {
-    final double iconSize = config.labels[index].icon.size ?? 24.0;
+  FractionalOffset _circleOffset(int index) {
+    final double iconSize = config.iconSize;
     final Tween<double> yOffsetTween = new Tween<double>(
       begin: (18.0 + iconSize / 2.0) / kBottomNavigationBarHeight, // 18dp + icon center
       end: (6.0 + iconSize / 2.0) / kBottomNavigationBarHeight     // 6dp + icon center
@@ -332,6 +342,7 @@ class BottomNavigationBarState extends State<BottomNavigationBar> with TickerPro
                         child: new IconTheme(
                           data: new IconThemeData(
                             color: colorTween.evaluate(animations[i]),
+                            size: config.iconSize,
                           ),
                           child: config.labels[i].icon,
                         ),
@@ -400,7 +411,8 @@ class BottomNavigationBarState extends State<BottomNavigationBar> with TickerPro
                         ),
                         child: new IconTheme(
                           data: new IconThemeData(
-                            color: Colors.white
+                            color: Colors.white,
+                            size: config.iconSize,
                           ),
                           child: config.labels[i].icon,
                         ),
@@ -507,7 +519,7 @@ class _Circle {
   CurvedAnimation animation;
 
   FractionalOffset get offset {
-    return state.cirleOffset(index);
+    return state._circleOffset(index);
   }
 
   void dispose() {

packages/flutter/test/material/bottom_navigation_bar_test.dart

@@ -240,4 +240,40 @@ void main() {
     await tester.pump(const Duration(seconds: 1));
     expect(Theme.of(tester.element(find.text('Alarm'))).brightness, equals(Brightness.dark));
   });
+
+  testWidgets('BottomNavigationBar iconSize test', (WidgetTester tester) async {
+    double builderIconSize;
+    await tester.pumpWidget(
+      new Scaffold(
+        bottomNavigationBar: new BottomNavigationBar(
+          iconSize: 12.0,
+          labels: <DestinationLabel>[
+            new DestinationLabel(
+              title: new Text('A'),
+              icon: new Icon(Icons.ac_unit),
+            ),
+            new DestinationLabel(
+              title: new Text('B'),
+              icon: new Builder(
+                builder: (BuildContext context) {
+                  builderIconSize = IconTheme.of(context).fallback().size;
+                  return new SizedBox(
+                    width: builderIconSize,
+                    height: builderIconSize,
+                  );
+                },
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+
+    RenderBox box = tester.renderObject(find.byType(Icon));
+    expect(box.size.width, equals(12.0));
+    expect(box.size.height, equals(12.0));
+    expect(builderIconSize, 12.0);
+  });
+
+
 }