switch_list_tile.dart

// 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 'list_tile.dart';
import 'switch.dart';
import 'theme.dart';
import 'theme_data.dart';

// Examples can assume:
// void setState(VoidCallback fn) { }
// bool _isSelected;

enum _SwitchListTileType { material, adaptive }

/// A [ListTile] with a [Switch]. In other words, a switch with a label.
///
/// {@youtube 560 315 https://www.youtube.com/watch?v=0igIjvtEWNU}
///
/// The entire list tile is interactive: tapping anywhere in the tile toggles
/// the switch. Tapping and dragging the [Switch] also triggers the [onChanged]
/// callback.
///
/// To ensure that [onChanged] correctly triggers, the state passed
/// into [value] must be properly managed. This is typically done by invoking
/// [State.setState] in [onChanged] to toggle the state value.
///
/// The [value], [onChanged], [activeColor], [activeThumbImage], and
/// [inactiveThumbImage] properties of this widget are identical to the
/// similarly-named properties on the [Switch] widget.
///
/// The [title], [subtitle], [isThreeLine], and [dense] properties are like
/// those of the same name on [ListTile].
///
/// The [selected] property on this widget is similar to the [ListTile.selected]
/// property. This tile's [activeColor] is used for the selected item's text color, or
/// the theme's [ThemeData.toggleableActiveColor] if [activeColor] is null.
///
/// This widget does not coordinate the [selected] state and the
/// [value]; to have the list tile appear selected when the
/// switch button is on, use the same value for both.
///
/// The switch is shown on the right by default in left-to-right languages (i.e.
/// in the [ListTile.trailing] slot) which can be changed using [controlAffinity].
/// The [secondary] widget is placed in the [ListTile.leading] slot.
///
/// To show the [SwitchListTile] as disabled, pass null as the [onChanged]
/// callback.
///
/// {@tool dartpad --template=stateful_widget_scaffold_center}
///
/// ![SwitchListTile sample](https://flutter.github.io/assets-for-api-docs/assets/material/switch_list_tile.png)
///
/// This widget shows a switch that, when toggled, changes the state of a [bool]
/// member field called `_lights`.
///
/// ```dart
/// bool _lights = false;
///
/// @override
/// Widget build(BuildContext context) {
///   return SwitchListTile(
///     title: const Text('Lights'),
///     value: _lights,
///     onChanged: (bool value) { setState(() { _lights = value; }); },
///     secondary: const Icon(Icons.lightbulb_outline),
///   );
/// }
/// ```
/// {@end-tool}
///
/// ## Semantics in SwitchListTile
///
/// Since the entirety of the SwitchListTile is interactive, it should represent
/// itself as a single interactive entity.
///
/// To do so, a SwitchListTile widget wraps its children with a [MergeSemantics]
/// widget. [MergeSemantics] will attempt to merge its descendant [Semantics]
/// nodes into one node in the semantics tree. Therefore, SwitchListTile will
/// throw an error if any of its children requires its own [Semantics] node.
///
/// For example, you cannot nest a [RichText] widget as a descendant of
/// SwitchListTile. [RichText] has an embedded gesture recognizer that
/// requires its own [Semantics] node, which directly conflicts with
/// SwitchListTile's desire to merge all its descendants' semantic nodes
/// into one. Therefore, it may be necessary to create a custom radio tile
/// widget to accommodate similar use cases.
///
/// {@tool dartpad --template=stateful_widget_scaffold_center}
///
/// ![Switch list tile semantics sample](https://flutter.github.io/assets-for-api-docs/assets/material/switch_list_tile_semantics.png)
///
/// Here is an example of a custom labeled radio widget, called
/// LinkedLabelRadio, that includes an interactive [RichText] widget that
/// handles tap gestures.
///
/// ```dart imports
/// import 'package:flutter/gestures.dart';
/// ```
/// ```dart preamble
/// class LinkedLabelSwitch extends StatelessWidget {
///   const LinkedLabelSwitch({
///     Key? key,
///     required this.label,
///     required this.padding,
///     required this.value,
///     required this.onChanged,
///   }) : super(key: key);
///
///   final String label;
///   final EdgeInsets padding;
///   final bool value;
///   final Function onChanged;
///
///   @override
///   Widget build(BuildContext context) {
///     return Padding(
///       padding: padding,
///       child: Row(
///         children: <Widget>[
///           Expanded(
///             child: RichText(
///               text: TextSpan(
///                 text: label,
///                 style: const TextStyle(
///                   color: Colors.blueAccent,
///                   decoration: TextDecoration.underline,
///                 ),
///                 recognizer: TapGestureRecognizer()
///                   ..onTap = () {
///                   print('Label has been tapped.');
///                 },
///               ),
///             ),
///           ),
///           Switch(
///             value: value,
///             onChanged: (bool newValue) {
///               onChanged(newValue);
///             },
///           ),
///         ],
///       ),
///     );
///   }
/// }
/// ```
/// ```dart
/// bool _isSelected = false;
///
/// @override
/// Widget build(BuildContext context) {
///   return LinkedLabelSwitch(
///     label: 'Linked, tappable label text',
///     padding: const EdgeInsets.symmetric(horizontal: 20.0),
///     value: _isSelected,
///     onChanged: (bool newValue) {
///       setState(() {
///         _isSelected = newValue;
///       });
///     },
///   );
/// }
/// ```
/// {@end-tool}
///
/// ## SwitchListTile isn't exactly what I want
///
/// If the way SwitchListTile pads and positions its elements isn't quite what
/// you're looking for, you can create custom labeled switch widgets by
/// combining [Switch] with other widgets, such as [Text], [Padding] and
/// [InkWell].
///
/// {@tool dartpad --template=stateful_widget_scaffold_center}
///
/// ![Custom switch list tile sample](https://flutter.github.io/assets-for-api-docs/assets/material/switch_list_tile_custom.png)
///
/// Here is an example of a custom LabeledSwitch widget, but you can easily
/// make your own configurable widget.
///
/// ```dart preamble
/// class LabeledSwitch extends StatelessWidget {
///   const LabeledSwitch({
///     Key? key,
///     required this.label,
///     required this.padding,
///     required this.value,
///     required this.onChanged,
///   }) : super(key: key);
///
///   final String label;
///   final EdgeInsets padding;
///   final bool value;
///   final Function onChanged;
///
///   @override
///   Widget build(BuildContext context) {
///     return InkWell(
///       onTap: () {
///         onChanged(!value);
///       },
///       child: Padding(
///         padding: padding,
///         child: Row(
///           children: <Widget>[
///             Expanded(child: Text(label)),
///             Switch(
///               value: value,
///               onChanged: (bool newValue) {
///                 onChanged(newValue);
///               },
///             ),
///           ],
///         ),
///       ),
///     );
///   }
/// }
/// ```
/// ```dart
/// bool _isSelected = false;
///
/// @override
/// Widget build(BuildContext context) {
///   return LabeledSwitch(
///     label: 'This is the label text',
///     padding: const EdgeInsets.symmetric(horizontal: 20.0),
///     value: _isSelected,
///     onChanged: (bool newValue) {
///       setState(() {
///         _isSelected = newValue;
///       });
///     },
///   );
/// }
/// ```
/// {@end-tool}
///
/// See also:
///
///  * [ListTileTheme], which can be used to affect the style of list tiles,
///    including switch list tiles.
///  * [CheckboxListTile], a similar widget for checkboxes.
///  * [RadioListTile], a similar widget for radio buttons.
///  * [ListTile] and [Switch], the widgets from which this widget is made.
class SwitchListTile extends StatelessWidget {
  /// Creates a combination of a list tile and a switch.
  ///
  /// The switch tile itself does not maintain any state. Instead, when the
  /// state of the switch changes, the widget calls the [onChanged] callback.
  /// Most widgets that use a switch will listen for the [onChanged] callback
  /// and rebuild the switch tile with a new [value] to update the visual
  /// appearance of the switch.
  ///
  /// The following arguments are required:
  ///
  /// * [value] determines whether this switch is on or off.
  /// * [onChanged] is called when the user toggles the switch on or off.
  const SwitchListTile({
    Key? key,
    required this.value,
    required this.onChanged,
    this.tileColor,
    this.activeColor,
    this.activeTrackColor,
    this.inactiveThumbColor,
    this.inactiveTrackColor,
    this.activeThumbImage,
    this.inactiveThumbImage,
    this.title,
    this.subtitle,
    this.isThreeLine = false,
    this.dense,
    this.contentPadding,
    this.secondary,
    this.selected = false,
    this.autofocus = false,
    this.controlAffinity = ListTileControlAffinity.platform,
    this.shape,
    this.selectedTileColor,
  }) : _switchListTileType = _SwitchListTileType.material,
       assert(value != null),
       assert(isThreeLine != null),
       assert(!isThreeLine || subtitle != null),
       assert(selected != null),
       assert(autofocus != null),
       super(key: key);

  /// Creates a Material [ListTile] with an adaptive [Switch], following
  /// Material design's
  /// [Cross-platform guidelines](https://material.io/design/platform-guidance/cross-platform-adaptation.html).
  ///
  /// This widget uses [Switch.adaptive] to change the graphics of the switch
  /// component based on the ambient [ThemeData.platform]. On iOS and macOS, a
  /// [CupertinoSwitch] will be used. On other platforms a Material design
  /// [Switch] will be used.
  ///
  /// If a [CupertinoSwitch] is created, the following parameters are
  /// ignored: [activeTrackColor], [inactiveThumbColor], [inactiveTrackColor],
  /// [activeThumbImage], [inactiveThumbImage].
  const SwitchListTile.adaptive({
    Key? key,
    required this.value,
    required this.onChanged,
    this.tileColor,
    this.activeColor,
    this.activeTrackColor,
    this.inactiveThumbColor,
    this.inactiveTrackColor,
    this.activeThumbImage,
    this.inactiveThumbImage,
    this.title,
    this.subtitle,
    this.isThreeLine = false,
    this.dense,
    this.contentPadding,
    this.secondary,
    this.selected = false,
    this.autofocus = false,
    this.controlAffinity = ListTileControlAffinity.platform,
    this.shape,
    this.selectedTileColor,
  }) : _switchListTileType = _SwitchListTileType.adaptive,
       assert(value != null),
       assert(isThreeLine != null),
       assert(!isThreeLine || subtitle != null),
       assert(selected != null),
       assert(autofocus != null),
       super(key: key);

  /// Whether this switch is checked.
  ///
  /// This property must not be null.
  final bool value;

  /// Called when the user toggles the switch on or off.
  ///
  /// The switch passes the new value to the callback but does not actually
  /// change state until the parent widget rebuilds the switch tile with the
  /// new value.
  ///
  /// If null, the switch will be displayed as disabled.
  ///
  /// The callback provided to [onChanged] should update the state of the parent
  /// [StatefulWidget] using the [State.setState] method, so that the parent
  /// gets rebuilt; for example:
  ///
  /// ```dart
  /// SwitchListTile(
  ///   value: _isSelected,
  ///   onChanged: (bool newValue) {
  ///     setState(() {
  ///       _isSelected = newValue;
  ///     });
  ///   },
  ///   title: Text('Selection'),
  /// )
  /// ```
  final ValueChanged<bool>? onChanged;

  /// The color to use when this switch is on.
  ///
  /// Defaults to accent color of the current [Theme].
  final Color? activeColor;

  /// The color to use on the track when this switch is on.
  ///
  /// Defaults to [ThemeData.toggleableActiveColor] with the opacity set at 50%.
  ///
  /// Ignored if created with [SwitchListTile.adaptive].
  final Color? activeTrackColor;

  /// The color to use on the thumb when this switch is off.
  ///
  /// Defaults to the colors described in the Material design specification.
  ///
  /// Ignored if created with [SwitchListTile.adaptive].
  final Color? inactiveThumbColor;

  /// The color to use on the track when this switch is off.
  ///
  /// Defaults to the colors described in the Material design specification.
  ///
  /// Ignored if created with [SwitchListTile.adaptive].
  final Color? inactiveTrackColor;

  /// {@macro flutter.material.ListTile.tileColor}
  final Color? tileColor;

  /// An image to use on the thumb of this switch when the switch is on.
  final ImageProvider? activeThumbImage;

  /// An image to use on the thumb of this switch when the switch is off.
  ///
  /// Ignored if created with [SwitchListTile.adaptive].
  final ImageProvider? inactiveThumbImage;

  /// The primary content of the list tile.
  ///
  /// Typically a [Text] widget.
  final Widget? title;

  /// Additional content displayed below the title.
  ///
  /// Typically a [Text] widget.
  final Widget? subtitle;

  /// A widget to display on the opposite side of the tile from the switch.
  ///
  /// Typically an [Icon] widget.
  final Widget? secondary;

  /// Whether this list tile is intended to display three lines of text.
  ///
  /// If false, the list tile is treated as having one line if the subtitle is
  /// null and treated as having two lines if the subtitle is non-null.
  final bool isThreeLine;

  /// Whether this list tile is part of a vertically dense list.
  ///
  /// If this property is null then its value is based on [ListTileTheme.dense].
  final bool? dense;

  /// The tile's internal padding.
  ///
  /// Insets a [SwitchListTile]'s contents: its [title], [subtitle],
  /// [secondary], and [Switch] widgets.
  ///
  /// If null, [ListTile]'s default of `EdgeInsets.symmetric(horizontal: 16.0)`
  /// is used.
  final EdgeInsetsGeometry? contentPadding;

  /// Whether to render icons and text in the [activeColor].
  ///
  /// No effort is made to automatically coordinate the [selected] state and the
  /// [value] state. To have the list tile appear selected when the switch is
  /// on, pass the same value to both.
  ///
  /// Normally, this property is left to its default value, false.
  final bool selected;

  /// {@macro flutter.widgets.Focus.autofocus}
  final bool autofocus;

  /// If adaptive, creates the switch with [Switch.adaptive].
  final _SwitchListTileType _switchListTileType;

  /// Defines the position of control and [secondary], relative to text.
  ///
  /// By default, the value of `controlAffinity` is [ListTileControlAffinity.platform].
  final ListTileControlAffinity controlAffinity;

  /// {@macro flutter.material.ListTileTheme.shape}
  final ShapeBorder? shape;

  /// If non-null, defines the background color when [SwitchListTile.selected] is true.
  final Color? selectedTileColor;

  @override
  Widget build(BuildContext context) {
    final Widget control;
    switch (_switchListTileType) {
      case _SwitchListTileType.adaptive:
        control = Switch.adaptive(
          value: value,
          onChanged: onChanged,
          activeColor: activeColor,
          activeThumbImage: activeThumbImage,
          inactiveThumbImage: inactiveThumbImage,
          materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
          activeTrackColor: activeTrackColor,
          inactiveTrackColor: inactiveTrackColor,
          inactiveThumbColor: inactiveThumbColor,
          autofocus: autofocus,
        );
        break;

      case _SwitchListTileType.material:
        control = Switch(
          value: value,
          onChanged: onChanged,
          activeColor: activeColor,
          activeThumbImage: activeThumbImage,
          inactiveThumbImage: inactiveThumbImage,
          materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
          activeTrackColor: activeTrackColor,
          inactiveTrackColor: inactiveTrackColor,
          inactiveThumbColor: inactiveThumbColor,
          autofocus: autofocus,
        );
    }

    Widget? leading, trailing;
    switch (controlAffinity) {
      case ListTileControlAffinity.leading:
        leading = control;
        trailing = secondary;
        break;
      case ListTileControlAffinity.trailing:
      case ListTileControlAffinity.platform:
        leading = secondary;
        trailing = control;
        break;
    }

    return MergeSemantics(
      child: ListTileTheme.merge(
        selectedColor: activeColor ?? Theme.of(context).toggleableActiveColor,
        child: ListTile(
          leading: leading,
          title: title,
          subtitle: subtitle,
          trailing: trailing,
          isThreeLine: isThreeLine,
          dense: dense,
          contentPadding: contentPadding,
          enabled: onChanged != null,
          onTap: onChanged != null ? () { onChanged!(!value); } : null,
          selected: selected,
          selectedTileColor: selectedTileColor,
          autofocus: autofocus,
          shape: shape,
          tileColor: tileColor,
        ),
      ),
    );
  }
}