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

// 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:flutter/widgets.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.
///
/// 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.
///
/// 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.children = const <Widget>[],
  }) : assert(buttonMinWidth == null || buttonMinWidth >= 0.0),
       assert(buttonHeight == null || buttonHeight >= 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;

  /// 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: Row(
        mainAxisAlignment: alignment ?? barTheme.alignment ?? MainAxisAlignment.end,
        mainAxisSize: mainAxisSize ?? barTheme.mainAxisSize ?? MainAxisSize.max,
        children: children.map<Widget>((Widget child) {
          return Padding(
            padding: EdgeInsets.symmetric(horizontal: paddingUnit),
            child: child,
          );
        }).toList(),
      ),
    );
    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;
  }
}