Version 0 of TabLabel, Tab, and TabBar components

There's is no support for animating the selected tab indicator, there isn't a TabNavigator container yet, overflow layout (tabs don't fit) isn't supported yet, etc.

R=abarth@chromium.org, ianh@google.com

Review URL: https://codereview.chromium.org/1205953002.

examples/widgets/tabs.dart

@@ -0,0 +1,62 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:sky/theme/colors.dart';
+import 'package:sky/theme/typography.dart';
+import 'package:sky/widgets/basic.dart';
+import 'package:sky/widgets/material.dart';
+import 'package:sky/widgets/scaffold.dart';
+import 'package:sky/widgets/tabs.dart';
+import 'package:sky/widgets/tool_bar.dart';
+import 'package:sky/widgets/widget.dart';
+
+class TabbedNavigatorApp extends App {
+  static Iterable<String> items = const <String>["ONE", "TWO", "FREE", "FOUR"];
+  final List<int> navigatorSelections = new List<int>.filled(items.length, 0);
+
+  Widget buildTabNavigator(Iterable<TabLabel> labels, int navigatorIndex) {
+    TabBar tabBar = new TabBar(
+      labels: labels.toList(),
+      selectedIndex: navigatorSelections[navigatorIndex],
+      onChanged: (selectionIndex) {
+        setState(() { 
+          navigatorSelections[navigatorIndex] = selectionIndex;
+        });
+      }
+    );
+
+    return new Container(child: tabBar, margin: new EdgeDims.only(bottom: 16.0));
+  }
+
+  Widget build() {
+    Iterable<TabLabel> textLabels = items
+      .map((s) => new TabLabel(text: "ITEM " + s));
+
+    Iterable<TabLabel> iconLabels = items
+      .map((s) => new TabLabel(icon: 'action/search_white'));
+
+    Iterable<TabLabel> textAndIconLabels = items
+      .map((s) => new TabLabel(text: "ITEM " + s, icon: 'action/search_white'));
+
+    var navigatorIndex = 0;
+    Iterable<Widget> tabNavigators = [textLabels, iconLabels, textAndIconLabels]
+      .map((labels) => buildTabNavigator(labels, navigatorIndex++));
+
+    ToolBar toolbar = new ToolBar(
+      center: new Text('Tabbed Navigator', style: white.title),
+      backgroundColor: Blue[500]);
+
+    return new Scaffold(
+      toolbar: toolbar,
+      body: new Material(
+        child: new Center(child: new Block(tabNavigators.toList())),
+        color: Grey[500]
+      )
+    );
+  }
+}
+
+void main() {
+  runApp(new TabbedNavigatorApp());
+}

sdk/BUILD.gn

@@ -119,6 +119,7 @@ dart_pkg("sdk") {
     "lib/widgets/scaffold.dart",
     "lib/widgets/scrollable.dart",
     "lib/widgets/switch.dart",
+    "lib/widgets/tabs.dart",
     "lib/widgets/theme.dart",
     "lib/widgets/toggleable.dart",
     "lib/widgets/tool_bar.dart",

sdk/lib/rendering/block.dart

@@ -28,11 +28,11 @@ class RenderBlock extends RenderBox with ContainerRenderObjectMixin<RenderBox, B
 
   double getMinIntrinsicWidth(BoxConstraints constraints) {
     double width = 0.0;
-    BoxConstraints innerConstraints = new BoxConstraints(
-        minWidth: constraints.minWidth, maxWidth: constraints.maxWidth);
+    BoxConstraints innerConstraints = constraints.widthConstraints();
     RenderBox child = firstChild;
     while (child != null) {
       width = math.max(width, child.getMinIntrinsicWidth(innerConstraints));
+      assert(child.parentData is BlockParentData);
       child = child.parentData.nextSibling;
     }
     return width;
@@ -40,11 +40,11 @@ class RenderBlock extends RenderBox with ContainerRenderObjectMixin<RenderBox, B
 
   double getMaxIntrinsicWidth(BoxConstraints constraints) {
     double width = 0.0;
-    BoxConstraints innerConstraints = new BoxConstraints(
-        minWidth: constraints.minWidth, maxWidth: constraints.maxWidth);
+    BoxConstraints innerConstraints = constraints.widthConstraints();
     RenderBox child = firstChild;
     while (child != null) {
       width = math.max(width, child.getMaxIntrinsicWidth(innerConstraints));
+      assert(child.parentData is BlockParentData);
       child = child.parentData.nextSibling;
     }
     return width;
@@ -63,6 +63,7 @@ class RenderBlock extends RenderBox with ContainerRenderObjectMixin<RenderBox, B
       double childHeight = child.getMinIntrinsicHeight(innerConstraints);
       assert(childHeight == child.getMaxIntrinsicHeight(innerConstraints));
       height += childHeight;
+      assert(child.parentData is BlockParentData);
       child = child.parentData.nextSibling;
     }
     return height;

sdk/lib/rendering/box.dart

@@ -163,6 +163,10 @@ class BoxConstraints extends Constraints {
                               maxHeight: math.min(maxHeight, newMaxHeight));
   }
 
+  BoxConstraints widthConstraints() => new BoxConstraints(minWidth: minWidth, maxWidth: maxWidth);
+
+  BoxConstraints heightConstraints() => new BoxConstraints(minHeight: minHeight, maxHeight: maxHeight);
+
   final double minWidth;
   final double maxWidth;
   final double minHeight;

sdk/lib/widgets/tabs.dart

@@ -0,0 +1,262 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:math' as math;
+import 'dart:sky' as sky;
+
+import 'package:sky/painting/text_style.dart';
+import 'package:sky/rendering/box.dart';
+import 'package:sky/rendering/object.dart';
+import 'package:sky/theme/colors.dart';
+import 'package:sky/widgets/basic.dart';
+import 'package:sky/widgets/icon.dart';
+import 'package:sky/widgets/ink_well.dart';
+import 'package:sky/widgets/widget.dart';
+
+typedef void SelectedIndexChanged(int selectedIndex);
+
+const double _kTabHeight = 46.0;
+const double _kTabIndicatorHeight = 2.0;
+const double _kTabBarHeight = _kTabHeight + _kTabIndicatorHeight;
+const double _kMinTabWidth = 72.0;
+
+class TabBarParentData extends BoxParentData with
+    ContainerParentDataMixin<RenderBox> { }
+
+class RenderTabBar extends RenderBox with
+    ContainerRenderObjectMixin<RenderBox, TabBarParentData>,
+    RenderBoxContainerDefaultsMixin<RenderBox, TabBarParentData> {
+
+  int _selectedIndex;
+  int get selectedIndex => _selectedIndex;
+  void set selectedIndex(int value) {
+    if (_selectedIndex != value) {
+      _selectedIndex = value;
+      markNeedsPaint();
+    }
+  }
+
+  void setParentData(RenderBox child) {
+    if (child.parentData is! TabBarParentData)
+      child.parentData = new TabBarParentData();
+  }
+
+  double getMinIntrinsicWidth(BoxConstraints constraints) {
+    BoxConstraints widthConstraints =
+        new BoxConstraints(maxWidth: constraints.maxWidth, maxHeight: constraints.maxHeight);
+    double maxWidth = 0.0;
+    int childCount = 0;
+    RenderBox child = firstChild;
+    while (child != null) {
+      maxWidth = math.max(maxWidth, child.getMinIntrinsicWidth(widthConstraints));
+      ++childCount;
+      assert(child.parentData is TabBarParentData);
+      child = child.parentData.nextSibling;
+    }
+    return constraints.constrainWidth(maxWidth * childCount);
+  }
+
+  double getMaxIntrinsicWidth(BoxConstraints constraints) {
+    BoxConstraints widthConstraints =
+        new BoxConstraints(maxWidth: constraints.maxWidth, maxHeight: constraints.maxHeight);
+    double maxWidth = 0.0;
+    int childCount = 0;
+    RenderBox child = firstChild;
+    while (child != null) {
+      maxWidth = math.max(maxWidth, child.getMaxIntrinsicWidth(widthConstraints));
+      ++childCount;
+      assert(child.parentData is TabBarParentData);
+      child = child.parentData.nextSibling;
+    }
+    return constraints.constrainWidth(maxWidth * childCount);
+  }
+
+  double _getIntrinsicHeight(BoxConstraints constraints) => constraints.constrainHeight(_kTabBarHeight);
+
+  double getMinIntrinsicHeight(BoxConstraints constraints) => _getIntrinsicHeight(constraints);
+
+  double getMaxIntrinsicHeight(BoxConstraints constraints) => _getIntrinsicHeight(constraints);
+
+  // TODO(hansmuller): track this value in the parent rather than computing it.
+  int _childCount() {
+    int childCount = 0;
+    RenderBox child = firstChild;
+    while (child != null) {
+      ++childCount;
+      assert(child.parentData is TabBarParentData);
+      child = child.parentData.nextSibling;
+    }
+    return childCount;
+  }
+
+  void performLayout() {
+    assert(constraints is BoxConstraints);
+
+    size = constraints.constrain(new Size(constraints.maxWidth, _kTabBarHeight));
+    assert(size.width < double.INFINITY);
+    assert(size.height < double.INFINITY);
+
+    int childCount = _childCount();
+    if (childCount == 0)
+      return;
+
+    double tabWidth = size.width / childCount;
+    BoxConstraints tabConstraints =
+      new BoxConstraints.tightFor(width: tabWidth, height: size.height);
+    double x = 0.0;
+    RenderBox child = firstChild;
+    while (child != null) {
+      child.layout(tabConstraints);
+      assert(child.parentData is TabBarParentData);
+      child.parentData.position = new Point(x, 0.0);
+      x += tabWidth;
+      child = child.parentData.nextSibling;
+    }
+  }
+
+  void hitTestChildren(HitTestResult result, { Point position }) {
+    defaultHitTestChildren(result, position: position);
+  }
+
+  void _paintIndicator(RenderCanvas canvas, RenderBox selectedTab) {
+    var size = new Size(selectedTab.size.width, _kTabIndicatorHeight);
+    var point = new Point(selectedTab.parentData.position.x, _kTabHeight);
+    Rect rect = new Rect.fromPointAndSize(point, size);
+    // TODO(hansmuller): indicator color should be based on the theme.
+    canvas.drawRect(rect, new Paint()..color = White);
+  }
+
+  void paint(RenderCanvas canvas) {
+    Rect rect = new Rect.fromSize(size);
+    canvas.drawRect(rect, new Paint()..color = Blue[500]);
+
+    int index = 0;
+    RenderBox child = firstChild;
+    while (child != null) {
+      assert(child.parentData is TabBarParentData);
+      canvas.paintChild(child, child.parentData.position);
+      if (index++ == selectedIndex)
+        _paintIndicator(canvas, child);
+      child = child.parentData.nextSibling;
+    }
+  }
+}
+
+class TabBarWrapper extends MultiChildRenderObjectWrapper {
+  TabBarWrapper(List<Widget> children, this.selectedIndex, { String key })
+    : super(key: key, children: children);
+
+  final int selectedIndex;
+
+  RenderTabBar get root => super.root;
+  RenderTabBar createNode() => new RenderTabBar();
+
+  void syncRenderObject(Widget old) {
+    super.syncRenderObject(old);
+    root.selectedIndex = selectedIndex;
+  }
+}
+
+class TabLabel {
+  const TabLabel({ this.text, this.icon });
+
+  final String text;
+  final String icon;
+}
+
+class Tab extends Component {
+  Tab({
+    String key,
+    this.label,
+    this.selected: false
+  }) : super(key: key) {
+    assert(label.text != null || label.icon != null);
+  }
+
+  final TabLabel label;
+  final bool selected;
+
+  // TODO(hansmuller): use themes here.
+  static const TextStyle selectedStyle = const TextStyle(color: const Color(0xFFFFFFFF));
+  static const TextStyle style = const TextStyle(color: const Color(0xB2FFFFFF));
+
+  Widget _buildLabelText() {
+    assert(label.text != null);
+    return new Text(label.text, style: style);
+  }
+
+  Widget _buildLabelIcon() {
+    assert(label.icon != null);
+    return new Icon(type: label.icon, size: 24);
+  }
+
+  Widget build() {
+    Widget labelContents;
+    if (label.icon == null) {
+      labelContents = _buildLabelText();
+    } else if (label.text == null) {
+      labelContents = _buildLabelIcon();
+    } else {
+      labelContents = new Flex(
+        <Widget>[_buildLabelText(), _buildLabelIcon()], 
+        justifyContent: FlexJustifyContent.center,
+        alignItems: FlexAlignItems.center,
+        direction: FlexDirection.vertical
+      );
+    }
+
+    Widget highlightedLabel = new Opacity(
+      child: labelContents, 
+      opacity: selected ? 1.0 : 0.7
+    );
+
+    Container centeredLabel = new Container(
+      child: new Center(child: highlightedLabel),
+      constraints: new BoxConstraints(minWidth: _kMinTabWidth)
+    );
+
+    return new InkWell(child: centeredLabel);
+  }
+}
+
+class TabBar extends Component {
+  TabBar({
+    String key,
+    this.labels,
+    this.selectedIndex: 0,
+    this.onChanged
+  }) : super(key: key);
+
+  final List<TabLabel> labels;
+  final int selectedIndex;
+  final SelectedIndexChanged onChanged;
+
+  void _handleTap(int tabIndex) {
+    if (tabIndex != selectedIndex && onChanged != null)
+      onChanged(tabIndex);
+  }
+
+  Widget _toTab(TabLabel label, int tabIndex) {
+    Tab tab = new Tab(
+      label: label,
+      selected: tabIndex == selectedIndex,
+      key: label.text == null ? label.icon : label.text
+    );
+    return new Listener(
+      child: tab,
+      onGestureTap: (_) => _handleTap(tabIndex)
+    );
+  }
+
+  Widget build() {
+    assert(labels != null && labels.isNotEmpty);
+    List<Widget> tabs = <Widget>[];
+    for (int tabIndex = 0; tabIndex < labels.length; tabIndex++) {
+      tabs.add(_toTab(labels[tabIndex], tabIndex));
+    }
+    return new TabBarWrapper(tabs, selectedIndex);
+  }
+}
+
+