packages/flutter/lib/src/material/button_bar.dart - mirrors/flutter - Git at Google

 // Copyright 2014 The Flutter 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:flutter/widgets.dart';
 import 'package:flutter/rendering.dart';

 import 'button_bar_theme.dart';
 import 'button_theme.dart';
 import 'dialog.dart';
 import 'flat_button.dart';
 import 'raised_button.dart';

 /// An end-aligned row of buttons, laying out into a column if there is not
 /// enough horizontal space.
 ///
 /// Places the buttons horizontally according to the [buttonPadding]. The
 /// children are laid out in a [Row] with [MainAxisAlignment.end]. When the
 /// [Directionality] is [TextDirection.ltr], the button bar's children are
 /// right justified and the last child becomes the rightmost child. When the
 /// [Directionality] [TextDirection.rtl] the children are left justified and
 /// the last child becomes the leftmost child.
 ///
 /// If the button bar's width exceeds the maximum width constraint on the
 /// widget, it aligns its buttons in a column. The key difference here
 /// is that the [MainAxisAlignment] will then be treated as a
 /// cross-axis/horizontal alignment. For example, if the buttons overflow and
 /// [ButtonBar.alignment] was set to [MainAxisAlignment.start], the buttons would
 /// align to the horizontal start of the button bar.
 ///
 /// The [ButtonBar] can be configured with a [ButtonBarTheme]. For any null
 /// property on the ButtonBar, the surrounding ButtonBarTheme's property
 /// will be used instead. If the ButtonBarTheme's property is null
 /// as well, the property will default to a value described in the field
 /// documentation below.
 ///
 /// The [children] are wrapped in a [ButtonTheme] that is a copy of the
 /// surrounding ButtonTheme with the button properties overridden by the
 /// properties of the ButtonBar as described above. These properties include
 /// [buttonTextTheme], [buttonMinWidth], [buttonHeight], [buttonPadding],
 /// and [buttonAlignedDropdown].
 ///
 /// Used by [Dialog] to arrange the actions at the bottom of the dialog.
 ///
 /// See also:
 ///
 ///  * [RaisedButton], a kind of button.
 ///  * [FlatButton], another kind of button.
 ///  * [Card], at the bottom of which it is common to place a [ButtonBar].
 ///  * [Dialog], which uses a [ButtonBar] for its actions.
 ///  * [ButtonBarTheme], which configures the [ButtonBar].
 class ButtonBar extends StatelessWidget {
   /// Creates a button bar.
   ///
   /// Both [buttonMinWidth] and [buttonHeight] must be non-negative if they
   /// are not null.
   const ButtonBar({
     Key key,
     this.alignment,
     this.mainAxisSize,
     this.buttonTextTheme,
     this.buttonMinWidth,
     this.buttonHeight,
     this.buttonPadding,
     this.buttonAlignedDropdown,
     this.layoutBehavior,
     this.overflowDirection,
     this.overflowButtonSpacing,
     this.children = const <Widget>[],
   }) : assert(buttonMinWidth == null || buttonMinWidth >= 0.0),
        assert(buttonHeight == null || buttonHeight >= 0.0),
        assert(overflowButtonSpacing == null || overflowButtonSpacing >= 0.0),
        super(key: key);

   /// How the children should be placed along the horizontal axis.
   ///
   /// If null then it will use [ButtonBarTheme.alignment]. If that is null,
   /// it will default to [MainAxisAlignment.end].
   final MainAxisAlignment alignment;

   /// How much horizontal space is available. See [Row.mainAxisSize].
   ///
   /// If null then it will use the surrounding [ButtonBarTheme.mainAxisSize].
   /// If that is null, it will default to [MainAxisSize.max].
   final MainAxisSize mainAxisSize;

   /// Overrides the surrounding [ButtonTheme.textTheme] to define a button's
   /// base colors, size, internal padding and shape.
   ///
   /// If null then it will use the surrounding [ButtonBarTheme.buttonTextTheme].
   /// If that is null, it will default to [ButtonTextTheme.primary].
   final ButtonTextTheme buttonTextTheme;

   /// Overrides the surrounding [ButtonThemeData.minWidth] to define a button's
   /// minimum width.
   ///
   /// If null then it will use the surrounding [ButtonBarTheme.buttonMinWidth].
   /// If that is null, it will default to 64.0 logical pixels.
   final double buttonMinWidth;

   /// Overrides the surrounding [ButtonThemeData.height] to define a button's
   /// minimum height.
   ///
   /// If null then it will use the surrounding [ButtonBarTheme.buttonHeight].
   /// If that is null, it will default to 36.0 logical pixels.
   final double buttonHeight;

   /// Overrides the surrounding [ButtonThemeData.padding] to define the padding
   /// for a button's child (typically the button's label).
   ///
   /// If null then it will use the surrounding [ButtonBarTheme.buttonPadding].
   /// If that is null, it will default to 8.0 logical pixels on the left
   /// and right.
   final EdgeInsetsGeometry buttonPadding;

   /// Overrides the surrounding [ButtonThemeData.alignedDropdown] to define whether
   /// a [DropdownButton] menu's width will match the button's width.
   ///
   /// If null then it will use the surrounding [ButtonBarTheme.buttonAlignedDropdown].
   /// If that is null, it will default to false.
   final bool buttonAlignedDropdown;

   /// Defines whether a [ButtonBar] should size itself with a minimum size
   /// constraint or with padding.
   ///
   /// Overrides the surrounding [ButtonThemeData.layoutBehavior].
   ///
   /// If null then it will use the surrounding [ButtonBarTheme.layoutBehavior].
   /// If that is null, it will default [ButtonBarLayoutBehavior.padded].
   final ButtonBarLayoutBehavior layoutBehavior;

   /// Defines the vertical direction of a [ButtonBar]'s children if it
   /// overflows.
   ///
   /// If [children] do not fit into a single row, then they
   /// are arranged in a column. The first action is at the top of the
   /// column if this property is set to [VerticalDirection.down], since it
   /// "starts" at the top and "ends" at the bottom. On the other hand,
   /// the first action will be at the bottom of the column if this
   /// property is set to [VerticalDirection.up], since it "starts" at the
   /// bottom and "ends" at the top.
   ///
   /// If null then it will use the surrounding
   /// [ButtonBarTheme.overflowDirection]. If that is null, it will
   /// default to [VerticalDirection.down].
   final VerticalDirection overflowDirection;

   /// The spacing between buttons when the button bar overflows.
   ///
   /// If the [children] do not fit into a single row, they are
   /// arranged into a column. This parameter provides additional
   /// vertical space in between buttons when it does overflow.
   ///
   /// Note that the button spacing may appear to be more than
   /// the value provided. This is because most buttons adhere to the
   /// [MaterialTapTargetSize] of 48px. So, even though a button
   /// might visually be 36px in height, it might still take up to
   /// 48px vertically.
   ///
   /// If null then no spacing will be added in between buttons in
   /// an overflow state.
   final double overflowButtonSpacing;

   /// The buttons to arrange horizontally.
   ///
   /// Typically [RaisedButton] or [FlatButton] widgets.
   final List<Widget> children;

   @override
   Widget build(BuildContext context) {
     final ButtonThemeData parentButtonTheme = ButtonTheme.of(context);
     final ButtonBarThemeData barTheme = ButtonBarTheme.of(context);

     final ButtonThemeData buttonTheme = parentButtonTheme.copyWith(
       textTheme: buttonTextTheme ?? barTheme.buttonTextTheme ?? ButtonTextTheme.primary,
       minWidth: buttonMinWidth ?? barTheme.buttonMinWidth ?? 64.0,
       height: buttonHeight ?? barTheme.buttonHeight ?? 36.0,
       padding: buttonPadding ?? barTheme.buttonPadding ?? const EdgeInsets.symmetric(horizontal: 8.0),
       alignedDropdown: buttonAlignedDropdown ?? barTheme.buttonAlignedDropdown ?? false,
       layoutBehavior: layoutBehavior ?? barTheme.layoutBehavior ?? ButtonBarLayoutBehavior.padded,
     );

     // We divide by 4.0 because we want half of the average of the left and right padding.
     final double paddingUnit = buttonTheme.padding.horizontal / 4.0;
     final Widget child = ButtonTheme.fromButtonThemeData(
       data: buttonTheme,
       child: _ButtonBarRow(
         mainAxisAlignment: alignment ?? barTheme.alignment ?? MainAxisAlignment.end,
         mainAxisSize: mainAxisSize ?? barTheme.mainAxisSize ?? MainAxisSize.max,
         overflowDirection: overflowDirection ?? barTheme.overflowDirection ?? VerticalDirection.down,
         children: children.map<Widget>((Widget child) {
           return Padding(
             padding: EdgeInsets.symmetric(horizontal: paddingUnit),
             child: child,
           );
         }).toList(),
         overflowButtonSpacing: overflowButtonSpacing,
       ),
     );
     switch (buttonTheme.layoutBehavior) {
       case ButtonBarLayoutBehavior.padded:
         return Padding(
           padding: EdgeInsets.symmetric(
             vertical: 2.0 * paddingUnit,
             horizontal: paddingUnit,
           ),
           child: child,
         );
       case ButtonBarLayoutBehavior.constrained:
         return Container(
           padding: EdgeInsets.symmetric(horizontal: paddingUnit),
           constraints: const BoxConstraints(minHeight: 52.0),
           alignment: Alignment.center,
           child: child,
         );
     }
     assert(false);
     return null;
   }
 }

 /// Attempts to display buttons in a row, but displays them in a column if
 /// there is not enough horizontal space.
 ///
 /// It first attempts to lay out its buttons as though there were no
 /// maximum width constraints on the widget. If the button bar's width is
 /// less than the maximum width constraints of the widget, it then lays
 /// out the widget as though it were placed in a [Row].
 ///
 /// However, if the button bar's width exceeds the maximum width constraint on
 /// the widget, it then aligns its buttons in a column. The key difference here
 /// is that the [MainAxisAlignment] will then be treated as a
 /// cross-axis/horizontal alignment. For example, if the buttons overflow and
 /// [ButtonBar.alignment] was set to [MainAxisAligment.start], the column of
 /// buttons would align to the horizontal start of the button bar.
 class _ButtonBarRow extends Flex {
   /// Creates a button bar that attempts to display in a row, but displays in
   /// a column if there is insufficient horizontal space.
   _ButtonBarRow({
     List<Widget> children,
     Axis direction = Axis.horizontal,
     MainAxisSize mainAxisSize = MainAxisSize.max,
     MainAxisAlignment mainAxisAlignment = MainAxisAlignment.start,
     CrossAxisAlignment crossAxisAlignment = CrossAxisAlignment.center,
     TextDirection textDirection,
     VerticalDirection overflowDirection = VerticalDirection.down,
     TextBaseline textBaseline,
     this.overflowButtonSpacing,
   }) : super(
     children: children,
     direction: direction,
     mainAxisSize: mainAxisSize,
     mainAxisAlignment: mainAxisAlignment,
     crossAxisAlignment: crossAxisAlignment,
     textDirection: textDirection,
     verticalDirection: overflowDirection,
     textBaseline: textBaseline,
   );

   final double overflowButtonSpacing;

   @override
   _RenderButtonBarRow createRenderObject(BuildContext context) {
     return _RenderButtonBarRow(
       direction: direction,
       mainAxisAlignment: mainAxisAlignment,
       mainAxisSize: mainAxisSize,
       crossAxisAlignment: crossAxisAlignment,
       textDirection: getEffectiveTextDirection(context),
       verticalDirection: verticalDirection,
       textBaseline: textBaseline,
       overflowButtonSpacing: overflowButtonSpacing,
     );
   }

   @override
   void updateRenderObject(BuildContext context, covariant _RenderButtonBarRow renderObject) {
     renderObject
       ..direction = direction
       ..mainAxisAlignment = mainAxisAlignment
       ..mainAxisSize = mainAxisSize
       ..crossAxisAlignment = crossAxisAlignment
       ..textDirection = getEffectiveTextDirection(context)
       ..verticalDirection = verticalDirection
       ..textBaseline = textBaseline
       ..overflowButtonSpacing = overflowButtonSpacing;
   }
 }

 /// Attempts to display buttons in a row, but displays them in a column if
 /// there is not enough horizontal space.
 ///
 /// It first attempts to lay out its buttons as though there were no
 /// maximum width constraints on the widget. If the button bar's width is
 /// less than the maximum width constraints of the widget, it then lays
 /// out the widget as though it were placed in a [Row].
 ///
 /// However, if the button bar's width exceeds the maximum width constraint on
 /// the widget, it then aligns its buttons in a column. The key difference here
 /// is that the [MainAxisAlignment] will then be treated as a
 /// cross-axis/horizontal alignment. For example, if the buttons overflow and
 /// [ButtonBar.alignment] was set to [MainAxisAligment.start], the buttons would
 /// align to the horizontal start of the button bar.
 class _RenderButtonBarRow extends RenderFlex {
   /// Creates a button bar that attempts to display in a row, but displays in
   /// a column if there is insufficient horizontal space.
   _RenderButtonBarRow({
     List<RenderBox> children,
     Axis direction = Axis.horizontal,
     MainAxisSize mainAxisSize = MainAxisSize.max,
     MainAxisAlignment mainAxisAlignment = MainAxisAlignment.start,
     CrossAxisAlignment crossAxisAlignment = CrossAxisAlignment.center,
     @required TextDirection textDirection,
     VerticalDirection verticalDirection = VerticalDirection.down,
     TextBaseline textBaseline,
     this.overflowButtonSpacing,
   }) : assert(textDirection != null),
        assert(overflowButtonSpacing == null || overflowButtonSpacing >= 0),
        super(
          children: children,
          direction: direction,
          mainAxisSize: mainAxisSize,
          mainAxisAlignment: mainAxisAlignment,
          crossAxisAlignment: crossAxisAlignment,
          textDirection: textDirection,
          verticalDirection: verticalDirection,
          textBaseline: textBaseline,
        );

   bool _hasCheckedLayoutWidth = false;
   double overflowButtonSpacing;

   @override
   BoxConstraints get constraints {
     if (_hasCheckedLayoutWidth)
       return super.constraints;
     return super.constraints.copyWith(maxWidth: double.infinity);
   }

   @override
   void performLayout() {
     // Set check layout width to false in reload or update cases.
     _hasCheckedLayoutWidth = false;

     // Perform layout to ensure that button bar knows how wide it would
     // ideally want to be.
     super.performLayout();
     _hasCheckedLayoutWidth = true;

     // If the button bar is constrained by width and it overflows, set the
     // buttons to align vertically. Otherwise, lay out the button bar
     // horizontally.
     if (size.width <= constraints.maxWidth) {
       // A second performLayout is required to ensure that the original maximum
       // width constraints are used. The original perform layout call assumes
       // a maximum width constraint of infinity.
       super.performLayout();
     } else {
       final BoxConstraints childConstraints = constraints.copyWith(minWidth: 0.0);
       RenderBox child;
       double currentHeight = 0.0;
       switch (verticalDirection) {
         case VerticalDirection.down:
           child = firstChild;
           break;
         case VerticalDirection.up:
           child = lastChild;
           break;
       }

       while (child != null) {
         final FlexParentData childParentData = child.parentData as FlexParentData;

         // Lay out the child with the button bar's original constraints, but
         // with minimum width set to zero.
         child.layout(childConstraints, parentUsesSize: true);

         // Set the cross axis alignment for the column to match the main axis
         // alignment for a row. For [MainAxisAligment.spaceAround],
         // [MainAxisAligment.spaceBetween] and [MainAxisAlignment.spaceEvenly]
         // cases, use [MainAxisAligmnent.start].
         switch (textDirection) {
           case TextDirection.ltr:
             switch (mainAxisAlignment) {
               case MainAxisAlignment.center:
                 final double midpoint = (constraints.maxWidth - child.size.width) / 2.0;
                 childParentData.offset = Offset(midpoint, currentHeight);
                 break;
               case MainAxisAlignment.end:
                 childParentData.offset = Offset(constraints.maxWidth - child.size.width, currentHeight);
                 break;
               default:
                 childParentData.offset = Offset(0, currentHeight);
                 break;
             }
             break;
           case TextDirection.rtl:
             switch (mainAxisAlignment) {
               case MainAxisAlignment.center:
                 final double midpoint = constraints.maxWidth / 2.0 - child.size.width / 2.0;
                 childParentData.offset = Offset(midpoint, currentHeight);
                 break;
               case MainAxisAlignment.end:
                 childParentData.offset = Offset(0, currentHeight);
                 break;
               default:
                 childParentData.offset = Offset(constraints.maxWidth - child.size.width, currentHeight);
                 break;
             }
             break;
         }
         currentHeight += child.size.height;
         switch (verticalDirection) {
           case VerticalDirection.down:
             child = childParentData.nextSibling;
             break;
           case VerticalDirection.up:
             child = childParentData.previousSibling;
             break;
         }

         if (overflowButtonSpacing != null && child != null)
           currentHeight += overflowButtonSpacing;
       }
       size = constraints.constrain(Size(constraints.maxWidth, currentHeight));
     }
   }
 }
	// Copyright 2014 The Flutter 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:flutter/widgets.dart';
	import 'package:flutter/rendering.dart';

	import 'button_bar_theme.dart';
	import 'button_theme.dart';
	import 'dialog.dart';
	import 'flat_button.dart';
	import 'raised_button.dart';

	/// An end-aligned row of buttons, laying out into a column if there is not
	/// enough horizontal space.
	///
	/// Places the buttons horizontally according to the [buttonPadding]. The
	/// children are laid out in a [Row] with [MainAxisAlignment.end]. When the
	/// [Directionality] is [TextDirection.ltr], the button bar's children are
	/// right justified and the last child becomes the rightmost child. When the
	/// [Directionality] [TextDirection.rtl] the children are left justified and
	/// the last child becomes the leftmost child.
	///
	/// If the button bar's width exceeds the maximum width constraint on the
	/// widget, it aligns its buttons in a column. The key difference here
	/// is that the [MainAxisAlignment] will then be treated as a
	/// cross-axis/horizontal alignment. For example, if the buttons overflow and
	/// [ButtonBar.alignment] was set to [MainAxisAlignment.start], the buttons would
	/// align to the horizontal start of the button bar.
	///
	/// The [ButtonBar] can be configured with a [ButtonBarTheme]. For any null
	/// property on the ButtonBar, the surrounding ButtonBarTheme's property
	/// will be used instead. If the ButtonBarTheme's property is null
	/// as well, the property will default to a value described in the field
	/// documentation below.
	///
	/// The [children] are wrapped in a [ButtonTheme] that is a copy of the
	/// surrounding ButtonTheme with the button properties overridden by the
	/// properties of the ButtonBar as described above. These properties include
	/// [buttonTextTheme], [buttonMinWidth], [buttonHeight], [buttonPadding],
	/// and [buttonAlignedDropdown].
	///
	/// Used by [Dialog] to arrange the actions at the bottom of the dialog.
	///
	/// See also:
	///
	/// * [RaisedButton], a kind of button.
	/// * [FlatButton], another kind of button.
	/// * [Card], at the bottom of which it is common to place a [ButtonBar].
	/// * [Dialog], which uses a [ButtonBar] for its actions.
	/// * [ButtonBarTheme], which configures the [ButtonBar].
	class ButtonBar extends StatelessWidget {
	/// Creates a button bar.
	///
	/// Both [buttonMinWidth] and [buttonHeight] must be non-negative if they
	/// are not null.
	const ButtonBar({
	Key key,
	this.alignment,
	this.mainAxisSize,
	this.buttonTextTheme,
	this.buttonMinWidth,
	this.buttonHeight,
	this.buttonPadding,
	this.buttonAlignedDropdown,
	this.layoutBehavior,
	this.overflowDirection,
	this.overflowButtonSpacing,
	this.children = const <Widget>[],
	}) : assert(buttonMinWidth == null \|\| buttonMinWidth >= 0.0),
	assert(buttonHeight == null \|\| buttonHeight >= 0.0),
	assert(overflowButtonSpacing == null \|\| overflowButtonSpacing >= 0.0),
	super(key: key);

	/// How the children should be placed along the horizontal axis.
	///
	/// If null then it will use [ButtonBarTheme.alignment]. If that is null,
	/// it will default to [MainAxisAlignment.end].
	final MainAxisAlignment alignment;

	/// How much horizontal space is available. See [Row.mainAxisSize].
	///
	/// If null then it will use the surrounding [ButtonBarTheme.mainAxisSize].
	/// If that is null, it will default to [MainAxisSize.max].
	final MainAxisSize mainAxisSize;

	/// Overrides the surrounding [ButtonTheme.textTheme] to define a button's
	/// base colors, size, internal padding and shape.
	///
	/// If null then it will use the surrounding [ButtonBarTheme.buttonTextTheme].
	/// If that is null, it will default to [ButtonTextTheme.primary].
	final ButtonTextTheme buttonTextTheme;

	/// Overrides the surrounding [ButtonThemeData.minWidth] to define a button's
	/// minimum width.
	///
	/// If null then it will use the surrounding [ButtonBarTheme.buttonMinWidth].
	/// If that is null, it will default to 64.0 logical pixels.
	final double buttonMinWidth;

	/// Overrides the surrounding [ButtonThemeData.height] to define a button's
	/// minimum height.
	///
	/// If null then it will use the surrounding [ButtonBarTheme.buttonHeight].
	/// If that is null, it will default to 36.0 logical pixels.
	final double buttonHeight;

	/// Overrides the surrounding [ButtonThemeData.padding] to define the padding
	/// for a button's child (typically the button's label).
	///
	/// If null then it will use the surrounding [ButtonBarTheme.buttonPadding].
	/// If that is null, it will default to 8.0 logical pixels on the left
	/// and right.
	final EdgeInsetsGeometry buttonPadding;

	/// Overrides the surrounding [ButtonThemeData.alignedDropdown] to define whether
	/// a [DropdownButton] menu's width will match the button's width.
	///
	/// If null then it will use the surrounding [ButtonBarTheme.buttonAlignedDropdown].
	/// If that is null, it will default to false.
	final bool buttonAlignedDropdown;

	/// Defines whether a [ButtonBar] should size itself with a minimum size
	/// constraint or with padding.
	///
	/// Overrides the surrounding [ButtonThemeData.layoutBehavior].
	///
	/// If null then it will use the surrounding [ButtonBarTheme.layoutBehavior].
	/// If that is null, it will default [ButtonBarLayoutBehavior.padded].
	final ButtonBarLayoutBehavior layoutBehavior;

	/// Defines the vertical direction of a [ButtonBar]'s children if it
	/// overflows.
	///
	/// If [children] do not fit into a single row, then they
	/// are arranged in a column. The first action is at the top of the
	/// column if this property is set to [VerticalDirection.down], since it
	/// "starts" at the top and "ends" at the bottom. On the other hand,
	/// the first action will be at the bottom of the column if this
	/// property is set to [VerticalDirection.up], since it "starts" at the
	/// bottom and "ends" at the top.
	///
	/// If null then it will use the surrounding
	/// [ButtonBarTheme.overflowDirection]. If that is null, it will
	/// default to [VerticalDirection.down].
	final VerticalDirection overflowDirection;

	/// The spacing between buttons when the button bar overflows.
	///
	/// If the [children] do not fit into a single row, they are
	/// arranged into a column. This parameter provides additional
	/// vertical space in between buttons when it does overflow.
	///
	/// Note that the button spacing may appear to be more than
	/// the value provided. This is because most buttons adhere to the
	/// [MaterialTapTargetSize] of 48px. So, even though a button
	/// might visually be 36px in height, it might still take up to
	/// 48px vertically.
	///
	/// If null then no spacing will be added in between buttons in
	/// an overflow state.
	final double overflowButtonSpacing;

	/// The buttons to arrange horizontally.
	///
	/// Typically [RaisedButton] or [FlatButton] widgets.
	final List<Widget> children;

	@override
	Widget build(BuildContext context) {
	final ButtonThemeData parentButtonTheme = ButtonTheme.of(context);
	final ButtonBarThemeData barTheme = ButtonBarTheme.of(context);

	final ButtonThemeData buttonTheme = parentButtonTheme.copyWith(
	textTheme: buttonTextTheme ?? barTheme.buttonTextTheme ?? ButtonTextTheme.primary,
	minWidth: buttonMinWidth ?? barTheme.buttonMinWidth ?? 64.0,
	height: buttonHeight ?? barTheme.buttonHeight ?? 36.0,
	padding: buttonPadding ?? barTheme.buttonPadding ?? const EdgeInsets.symmetric(horizontal: 8.0),
	alignedDropdown: buttonAlignedDropdown ?? barTheme.buttonAlignedDropdown ?? false,
	layoutBehavior: layoutBehavior ?? barTheme.layoutBehavior ?? ButtonBarLayoutBehavior.padded,
	);

	// We divide by 4.0 because we want half of the average of the left and right padding.
	final double paddingUnit = buttonTheme.padding.horizontal / 4.0;
	final Widget child = ButtonTheme.fromButtonThemeData(
	data: buttonTheme,
	child: _ButtonBarRow(
	mainAxisAlignment: alignment ?? barTheme.alignment ?? MainAxisAlignment.end,
	mainAxisSize: mainAxisSize ?? barTheme.mainAxisSize ?? MainAxisSize.max,
	overflowDirection: overflowDirection ?? barTheme.overflowDirection ?? VerticalDirection.down,
	children: children.map<Widget>((Widget child) {
	return Padding(
	padding: EdgeInsets.symmetric(horizontal: paddingUnit),
	child: child,
	);
	}).toList(),
	overflowButtonSpacing: overflowButtonSpacing,
	),
	);
	switch (buttonTheme.layoutBehavior) {
	case ButtonBarLayoutBehavior.padded:
	return Padding(
	padding: EdgeInsets.symmetric(
	vertical: 2.0 * paddingUnit,
	horizontal: paddingUnit,
	),
	child: child,
	);
	case ButtonBarLayoutBehavior.constrained:
	return Container(
	padding: EdgeInsets.symmetric(horizontal: paddingUnit),
	constraints: const BoxConstraints(minHeight: 52.0),
	alignment: Alignment.center,
	child: child,
	);
	}
	assert(false);
	return null;
	}
	}

	/// Attempts to display buttons in a row, but displays them in a column if
	/// there is not enough horizontal space.
	///
	/// It first attempts to lay out its buttons as though there were no
	/// maximum width constraints on the widget. If the button bar's width is
	/// less than the maximum width constraints of the widget, it then lays
	/// out the widget as though it were placed in a [Row].
	///
	/// However, if the button bar's width exceeds the maximum width constraint on
	/// the widget, it then aligns its buttons in a column. The key difference here
	/// is that the [MainAxisAlignment] will then be treated as a
	/// cross-axis/horizontal alignment. For example, if the buttons overflow and
	/// [ButtonBar.alignment] was set to [MainAxisAligment.start], the column of
	/// buttons would align to the horizontal start of the button bar.
	class _ButtonBarRow extends Flex {
	/// Creates a button bar that attempts to display in a row, but displays in
	/// a column if there is insufficient horizontal space.
	_ButtonBarRow({
	List<Widget> children,
	Axis direction = Axis.horizontal,
	MainAxisSize mainAxisSize = MainAxisSize.max,
	MainAxisAlignment mainAxisAlignment = MainAxisAlignment.start,
	CrossAxisAlignment crossAxisAlignment = CrossAxisAlignment.center,
	TextDirection textDirection,
	VerticalDirection overflowDirection = VerticalDirection.down,
	TextBaseline textBaseline,
	this.overflowButtonSpacing,
	}) : super(
	children: children,
	direction: direction,
	mainAxisSize: mainAxisSize,
	mainAxisAlignment: mainAxisAlignment,
	crossAxisAlignment: crossAxisAlignment,
	textDirection: textDirection,
	verticalDirection: overflowDirection,
	textBaseline: textBaseline,
	);

	final double overflowButtonSpacing;

	@override
	_RenderButtonBarRow createRenderObject(BuildContext context) {
	return _RenderButtonBarRow(
	direction: direction,
	mainAxisAlignment: mainAxisAlignment,
	mainAxisSize: mainAxisSize,
	crossAxisAlignment: crossAxisAlignment,
	textDirection: getEffectiveTextDirection(context),
	verticalDirection: verticalDirection,
	textBaseline: textBaseline,
	overflowButtonSpacing: overflowButtonSpacing,
	);
	}

	@override
	void updateRenderObject(BuildContext context, covariant _RenderButtonBarRow renderObject) {
	renderObject
	..direction = direction
	..mainAxisAlignment = mainAxisAlignment
	..mainAxisSize = mainAxisSize
	..crossAxisAlignment = crossAxisAlignment
	..textDirection = getEffectiveTextDirection(context)
	..verticalDirection = verticalDirection
	..textBaseline = textBaseline
	..overflowButtonSpacing = overflowButtonSpacing;
	}
	}

	/// Attempts to display buttons in a row, but displays them in a column if
	/// there is not enough horizontal space.
	///
	/// It first attempts to lay out its buttons as though there were no
	/// maximum width constraints on the widget. If the button bar's width is
	/// less than the maximum width constraints of the widget, it then lays
	/// out the widget as though it were placed in a [Row].
	///
	/// However, if the button bar's width exceeds the maximum width constraint on
	/// the widget, it then aligns its buttons in a column. The key difference here
	/// is that the [MainAxisAlignment] will then be treated as a
	/// cross-axis/horizontal alignment. For example, if the buttons overflow and
	/// [ButtonBar.alignment] was set to [MainAxisAligment.start], the buttons would
	/// align to the horizontal start of the button bar.
	class _RenderButtonBarRow extends RenderFlex {
	/// Creates a button bar that attempts to display in a row, but displays in
	/// a column if there is insufficient horizontal space.
	_RenderButtonBarRow({
	List<RenderBox> children,
	Axis direction = Axis.horizontal,
	MainAxisSize mainAxisSize = MainAxisSize.max,
	MainAxisAlignment mainAxisAlignment = MainAxisAlignment.start,
	CrossAxisAlignment crossAxisAlignment = CrossAxisAlignment.center,
	@required TextDirection textDirection,
	VerticalDirection verticalDirection = VerticalDirection.down,
	TextBaseline textBaseline,
	this.overflowButtonSpacing,
	}) : assert(textDirection != null),
	assert(overflowButtonSpacing == null \|\| overflowButtonSpacing >= 0),
	super(
	children: children,
	direction: direction,
	mainAxisSize: mainAxisSize,
	mainAxisAlignment: mainAxisAlignment,
	crossAxisAlignment: crossAxisAlignment,
	textDirection: textDirection,
	verticalDirection: verticalDirection,
	textBaseline: textBaseline,
	);

	bool _hasCheckedLayoutWidth = false;
	double overflowButtonSpacing;

	@override
	BoxConstraints get constraints {
	if (_hasCheckedLayoutWidth)
	return super.constraints;
	return super.constraints.copyWith(maxWidth: double.infinity);
	}

	@override
	void performLayout() {
	// Set check layout width to false in reload or update cases.
	_hasCheckedLayoutWidth = false;

	// Perform layout to ensure that button bar knows how wide it would
	// ideally want to be.
	super.performLayout();
	_hasCheckedLayoutWidth = true;

	// If the button bar is constrained by width and it overflows, set the
	// buttons to align vertically. Otherwise, lay out the button bar
	// horizontally.
	if (size.width <= constraints.maxWidth) {
	// A second performLayout is required to ensure that the original maximum
	// width constraints are used. The original perform layout call assumes
	// a maximum width constraint of infinity.
	super.performLayout();
	} else {
	final BoxConstraints childConstraints = constraints.copyWith(minWidth: 0.0);
	RenderBox child;
	double currentHeight = 0.0;
	switch (verticalDirection) {
	case VerticalDirection.down:
	child = firstChild;
	break;
	case VerticalDirection.up:
	child = lastChild;
	break;
	}

	while (child != null) {
	final FlexParentData childParentData = child.parentData as FlexParentData;

	// Lay out the child with the button bar's original constraints, but
	// with minimum width set to zero.
	child.layout(childConstraints, parentUsesSize: true);

	// Set the cross axis alignment for the column to match the main axis
	// alignment for a row. For [MainAxisAligment.spaceAround],
	// [MainAxisAligment.spaceBetween] and [MainAxisAlignment.spaceEvenly]
	// cases, use [MainAxisAligmnent.start].
	switch (textDirection) {
	case TextDirection.ltr:
	switch (mainAxisAlignment) {
	case MainAxisAlignment.center:
	final double midpoint = (constraints.maxWidth - child.size.width) / 2.0;
	childParentData.offset = Offset(midpoint, currentHeight);
	break;
	case MainAxisAlignment.end:
	childParentData.offset = Offset(constraints.maxWidth - child.size.width, currentHeight);
	break;
	default:
	childParentData.offset = Offset(0, currentHeight);
	break;
	}
	break;
	case TextDirection.rtl:
	switch (mainAxisAlignment) {
	case MainAxisAlignment.center:
	final double midpoint = constraints.maxWidth / 2.0 - child.size.width / 2.0;
	childParentData.offset = Offset(midpoint, currentHeight);
	break;
	case MainAxisAlignment.end:
	childParentData.offset = Offset(0, currentHeight);
	break;
	default:
	childParentData.offset = Offset(constraints.maxWidth - child.size.width, currentHeight);
	break;
	}
	break;
	}
	currentHeight += child.size.height;
	switch (verticalDirection) {
	case VerticalDirection.down:
	child = childParentData.nextSibling;
	break;
	case VerticalDirection.up:
	child = childParentData.previousSibling;
	break;
	}

	if (overflowButtonSpacing != null && child != null)
	currentHeight += overflowButtonSpacing;
	}
	size = constraints.constrain(Size(constraints.maxWidth, currentHeight));
	}
	}
	}