Implement ButtonBar, and Demo

Samples/MaterialSample/DividerButtonCanvas.cs

                                     )
                                 ),
                                 new Divider(),
-                                new Container(
-                                    width: 100,
-                                    height: 50,
-                                    child: new FlatButton(
-                                        onPressed: () => {
-                                            setState(() => {
-                                                title = controller.text;
-                                            });
-                                        },
-                                        padding: EdgeInsets.all(5.0),
-                                        child: new Center(
-                                            child: new Text("Set Title")
+                                new ButtonBar(
+                                    children: new List<Widget> {
+                                        new FlatButton(
+                                            onPressed: () => {
+                                                setState(() => {
+                                                    title = controller.text;
+                                                });
+                                            },
+                                            padding: EdgeInsets.all(5.0),
+                                            child: new Center(
+                                                child: new Text("Set Title")
+                                            )
+                                        ),
+                                        new RaisedButton(
+                                            onPressed: () => {
+                                                setState(() => {
+                                                    subtitle = controller.text;
+                                                });
+                                            },
+                                            padding: EdgeInsets.all(5.0),
+                                            child: new Center(
+                                                child: new Text("Set Subtitle")
+                                            )
-                                    )
-                                ),
-                                new Divider(),
-                                new Container(
-                                    width: 100,
-                                    height: 50,
-                                    child: new RaisedButton(
-                                        onPressed: () => {
-                                            setState(() => {
-                                                subtitle = controller.text;
-                                            });
-                                        },
-                                        padding: EdgeInsets.all(5.0),
-                                        child: new Center(
-                                            child: new Text("Set Subtitle")
-                                        )
-                                    )
+                                    }
                                 )
                             }
                         )

Runtime/material/button_bar.cs

+using System;
+using System.Collections;
+using System.Collections.Generic;
+using Unity.UIWidgets.rendering;
+using Unity.UIWidgets.foundation;
+using Unity.UIWidgets.painting;
+using Unity.UIWidgets.gestures;
+using Unity.UIWidgets.service;
+using Unity.UIWidgets.ui;
+using Unity.UIWidgets.widgets;
+
+namespace Unity.UIWidgets.material {
+
+    public class ButtonBar : StatelessWidget {
+
+        public ButtonBar(
+            Key key = null,
+            MainAxisAlignment alignment = MainAxisAlignment.end,
+            MainAxisSize mainAxisSize = MainAxisSize.max,
+            List<Widget> children = null
+        ) : base(key : key) {
+            this.alignment = alignment;
+            this.mainAxisSize = mainAxisSize;
+            this.children = children ?? new List<Widget>();
+        }
+
+        public readonly MainAxisAlignment alignment;
+        public readonly MainAxisSize mainAxisSize;
+        public readonly List<Widget> children;
+
+        public override Widget build(BuildContext context) {
+            ButtonThemeData buttonTheme = ButtonTheme.of(context);
+            double paddingUnit = buttonTheme.padding.horizontal / 4.0;
+            List<Widget> _children = new List<Widget>();
+            foreach(Widget _child in children) {
+                _children.Add(new Padding(
+                    padding: EdgeInsets.symmetric(horizontal: paddingUnit),
+                    child: _child
+                ));
+            }
+            Widget child = new Row(
+                mainAxisAlignment: alignment,
+                mainAxisSize: mainAxisSize,
+                children: _children
+            );
+            switch(buttonTheme.layoutBehavior) {
+            case ButtonBarLayoutBehavior.padded:
+                return new Padding(
+                  padding: EdgeInsets.symmetric(
+                    vertical: 2.0 * paddingUnit,
+                    horizontal: paddingUnit
+                  ),
+                  child: child
+                );
+            case ButtonBarLayoutBehavior.constrained:
+                return new Container(
+                    padding: EdgeInsets.symmetric(horizontal: paddingUnit),
+                    constraints: new BoxConstraints(minHeight: 52.0),
+                    alignment: Alignment.center,
+                    child: child
+                );
+            }
+            D.assert(false);
+            return null;
+        }
+    }
+}