radio_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 'list_tile_theme.dart';
import 'radio.dart';
import 'theme.dart';
import 'theme_data.dart';

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

/// A [ListTile] with a [Radio]. In other words, a radio button with a label.
///
/// The entire list tile is interactive: tapping anywhere in the tile selects
/// the radio button.
///
/// The [value], [groupValue], [onChanged], and [activeColor] properties of this
/// widget are identical to the similarly-named properties on the [Radio]
/// widget. The type parameter `T` serves the same purpose as that of the
/// [Radio] class' type parameter.
///
/// 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
/// [checked] state; to have the list tile appear selected when the
/// radio button is the selected radio button, set [selected] to true
/// when [value] matches [groupValue].
///
/// The radio button is shown on the left by default in left-to-right languages
/// (i.e. the leading edge). This can be changed using [controlAffinity]. The
/// [secondary] widget is placed on the opposite side. This maps to the
/// [ListTile.leading] and [ListTile.trailing] properties of [ListTile].
///
/// To show the [RadioListTile] as disabled, pass null as the [onChanged]
/// callback.
///
/// {@tool dartpad}
/// ![RadioListTile sample](https://flutter.github.io/assets-for-api-docs/assets/material/radio_list_tile.png)
///
/// This widget shows a pair of radio buttons that control the `_character`
/// field. The field is of the type `SingingCharacter`, an enum.
///
/// ** See code in examples/api/lib/material/radio_list_tile/radio_list_tile.0.dart **
/// {@end-tool}
///
/// ## Semantics in RadioListTile
///
/// Since the entirety of the RadioListTile is interactive, it should represent
/// itself as a single interactive entity.
///
/// To do so, a RadioListTile 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, RadioListTile 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
/// RadioListTile. [RichText] has an embedded gesture recognizer that
/// requires its own [Semantics] node, which directly conflicts with
/// RadioListTile'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}
/// ![Radio list tile semantics sample](https://flutter.github.io/assets-for-api-docs/assets/material/radio_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.
///
/// ** See code in examples/api/lib/material/radio_list_tile/radio_list_tile.1.dart **
/// {@end-tool}
///
/// ## RadioListTile isn't exactly what I want
///
/// If the way RadioListTile pads and positions its elements isn't quite what
/// you're looking for, you can create custom labeled radio widgets by
/// combining [Radio] with other widgets, such as [Text], [Padding] and
/// [InkWell].
///
/// {@tool dartpad}
/// ![Custom radio list tile sample](https://flutter.github.io/assets-for-api-docs/assets/material/radio_list_tile_custom.png)
///
/// Here is an example of a custom LabeledRadio widget, but you can easily
/// make your own configurable widget.
///
/// ** See code in examples/api/lib/material/radio_list_tile/radio_list_tile.2.dart **
/// {@end-tool}
///
/// See also:
///
///  * [ListTileTheme], which can be used to affect the style of list tiles,
///    including radio list tiles.
///  * [CheckboxListTile], a similar widget for checkboxes.
///  * [SwitchListTile], a similar widget for switches.
///  * [ListTile] and [Radio], the widgets from which this widget is made.
class RadioListTile<T> extends StatelessWidget {
  /// Creates a combination of a list tile and a radio button.
  ///
  /// The radio tile itself does not maintain any state. Instead, when the radio
  /// button is selected, the widget calls the [onChanged] callback. Most
  /// widgets that use a radio button will listen for the [onChanged] callback
  /// and rebuild the radio tile with a new [groupValue] to update the visual
  /// appearance of the radio button.
  ///
  /// The following arguments are required:
  ///
  /// * [value] and [groupValue] together determine whether the radio button is
  ///   selected.
  /// * [onChanged] is called when the user selects this radio button.
  const RadioListTile({
    super.key,
    required this.value,
    required this.groupValue,
    required this.onChanged,
    this.toggleable = false,
    this.activeColor,
    this.title,
    this.subtitle,
    this.isThreeLine = false,
    this.dense,
    this.secondary,
    this.selected = false,
    this.controlAffinity = ListTileControlAffinity.platform,
    this.autofocus = false,
    this.contentPadding,
    this.shape,
    this.tileColor,
    this.selectedTileColor,
    this.visualDensity,
    this.focusNode,
    this.enableFeedback,
  }) : assert(toggleable != null),
       assert(isThreeLine != null),
       assert(!isThreeLine || subtitle != null),
       assert(selected != null),
       assert(controlAffinity != null),
       assert(autofocus != null);

  /// The value represented by this radio button.
  final T value;

  /// The currently selected value for this group of radio buttons.
  ///
  /// This radio button is considered selected if its [value] matches the
  /// [groupValue].
  final T? groupValue;

  /// Called when the user selects this radio button.
  ///
  /// The radio button passes [value] as a parameter to this callback. The radio
  /// button does not actually change state until the parent widget rebuilds the
  /// radio tile with the new [groupValue].
  ///
  /// If null, the radio button will be displayed as disabled.
  ///
  /// The provided callback will not be invoked if this radio button is already
  /// selected.
  ///
  /// 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
  /// RadioListTile<SingingCharacter>(
  ///   title: const Text('Lafayette'),
  ///   value: SingingCharacter.lafayette,
  ///   groupValue: _character,
  ///   onChanged: (SingingCharacter newValue) {
  ///     setState(() {
  ///       _character = newValue;
  ///     });
  ///   },
  /// )
  /// ```
  final ValueChanged<T?>? onChanged;

  /// Set to true if this radio list tile is allowed to be returned to an
  /// indeterminate state by selecting it again when selected.
  ///
  /// To indicate returning to an indeterminate state, [onChanged] will be
  /// called with null.
  ///
  /// If true, [onChanged] can be called with [value] when selected while
  /// [groupValue] != [value], or with null when selected again while
  /// [groupValue] == [value].
  ///
  /// If false, [onChanged] will be called with [value] when it is selected
  /// while [groupValue] != [value], and only by selecting another radio button
  /// in the group (i.e. changing the value of [groupValue]) can this radio
  /// list tile be unselected.
  ///
  /// The default is false.
  ///
  /// {@tool dartpad}
  /// This example shows how to enable deselecting a radio button by setting the
  /// [toggleable] attribute.
  ///
  /// ** See code in examples/api/lib/material/radio_list_tile/radio_list_tile.toggleable.0.dart **
  /// {@end-tool}
  final bool toggleable;

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

  /// 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 radio button.
  ///
  /// 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 [ListTileThemeData.dense].
  final bool? dense;

  /// Whether to render icons and text in the [activeColor].
  ///
  /// No effort is made to automatically coordinate the [selected] state and the
  /// [checked] state. To have the list tile appear selected when the radio
  /// button is the selected radio button, set [selected] to true when [value]
  /// matches [groupValue].
  ///
  /// Normally, this property is left to its default value, false.
  final bool selected;

  /// Where to place the control relative to the text.
  final ListTileControlAffinity controlAffinity;

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

  /// Defines the insets surrounding the contents of the tile.
  ///
  /// Insets the [Radio], [title], [subtitle], and [secondary] widgets
  /// in [RadioListTile].
  ///
  /// When null, `EdgeInsets.symmetric(horizontal: 16.0)` is used.
  final EdgeInsetsGeometry? contentPadding;

  /// Whether this radio button is checked.
  ///
  /// To control this value, set [value] and [groupValue] appropriately.
  bool get checked => value == groupValue;

  /// If specified, [shape] defines the shape of the [RadioListTile]'s [InkWell] border.
  final ShapeBorder? shape;

  /// If specified, defines the background color for `RadioListTile` when
  /// [RadioListTile.selected] is false.
  final Color? tileColor;

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

  /// Defines how compact the list tile's layout will be.
  ///
  /// {@macro flutter.material.themedata.visualDensity}
  final VisualDensity? visualDensity;

  /// {@macro flutter.widgets.Focus.focusNode}
  final FocusNode? focusNode;

  /// {@macro flutter.material.ListTile.enableFeedback}
  ///
  /// See also:
  ///
  ///  * [Feedback] for providing platform-specific feedback to certain actions.
  final bool? enableFeedback;

  @override
  Widget build(BuildContext context) {
    final Widget control = Radio<T>(
      value: value,
      groupValue: groupValue,
      onChanged: onChanged,
      toggleable: toggleable,
      activeColor: activeColor,
      materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
      autofocus: autofocus,
    );
    Widget? leading, trailing;
    switch (controlAffinity) {
      case ListTileControlAffinity.leading:
      case ListTileControlAffinity.platform:
        leading = control;
        trailing = secondary;
        break;
      case ListTileControlAffinity.trailing:
        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,
          enabled: onChanged != null,
          shape: shape,
          tileColor: tileColor,
          selectedTileColor: selectedTileColor,
          onTap: onChanged != null ? () {
            if (toggleable && checked) {
              onChanged!(null);
              return;
            }
            if (!checked) {
              onChanged!(value);
            }
          } : null,
          selected: selected,
          autofocus: autofocus,
          contentPadding: contentPadding,
          visualDensity: visualDensity,
          focusNode: focusNode,
          enableFeedback: enableFeedback,
        ),
      ),
    );
  }
}