build method

@override Widget build(BuildContext context)

Describes the part of the user interface represented by this widget.

The framework calls this method when this widget is inserted into the tree in a given BuildContext and when the dependencies of this widget change (e.g., an InheritedWidget referenced by this widget changes). This method can potentially be called in every frame and should not have any side effects beyond building a widget.

The framework replaces the subtree below this widget with the widget returned by this method, either by updating the existing subtree or by removing the subtree and inflating a new subtree, depending on whether the widget returned by this method can update the root of the existing subtree, as determined by calling Widget.canUpdate.

Typically implementations return a newly created constellation of widgets that are configured with information from this widget's constructor and from the given BuildContext.

The given BuildContext contains information about the location in the tree at which this widget is being built. For example, the context provides the set of inherited widgets for this location in the tree. A given widget might be built with multiple different BuildContext arguments over time if the widget is moved around the tree or if the widget is inserted into the tree in multiple places at once.

The implementation of this method must only depend on:

• the fields of the widget, which themselves must not change over time, and
• any ambient state obtained from the context using BuildContext.dependOnInheritedWidgetOfExactType.

If a widget's build method is to depend on anything else, use a StatefulWidget instead.

See also:

• StatelessWidget, which contains the discussion on performance considerations.

Implementation

@override
Widget build(BuildContext context) {
  final effectiveColors = colors ??
      MiuixRadioButtonPreferenceDefaults.radioButtonPreferenceColors(context);
  final effectiveRadioButtonColors = radioButtonColors ??
      MiuixRadioButtonDefaults.radioButtonColors(context);

  final bool interactive = enabled && onClick != null;
  // 单选按钮在 Kotlin 中 onClick=null（仅作视觉指示），整行点击触发 onClick。
  // 为保持视觉启用态（MiuixRadioButton 把 onChanged=null 视为禁用并变灰），
  // 这里把行的点击行为同样挂到单选按钮上：点击单选按钮也会触发 onClick。
  final ValueChanged<bool>? radioButtonCallback =
      interactive ? (_) => _tap() : null;

  final Widget radioButtonWidget = MiuixRadioButton(
    selected: selected,
    onChanged: radioButtonCallback,
    enabled: enabled,
    colors: effectiveRadioButtonColors,
  );

  // 起始侧：单选按钮（如果在起始）+ 调用方 startAction。
  final Widget? startActionWidget;
  if (radioButtonLocation == MiuixRadioButtonLocation.start ||
      startAction != null) {
    startActionWidget = Row(
      mainAxisSize: MainAxisSize.min,
      children: <Widget>[
        if (radioButtonLocation == MiuixRadioButtonLocation.start)
          Padding(
            padding: const EdgeInsetsDirectional.only(end: 5),
            child: radioButtonWidget,
          ),
        if (startAction != null)
          Flexible(
            fit: FlexFit.loose,
            flex: 1,
            child: Padding(
              padding: const EdgeInsetsDirectional.only(end: 5),
              child: startAction!,
            ),
          ),
      ],
    );
  } else {
    startActionWidget = null;
  }

  // 末尾侧：调用方 endActions + 单选按钮（如果在末尾）。
  final hasExtraEndActions = endActions != null && endActions!.isNotEmpty;
  final List<Widget>? endActionsWithRadioButton;
  if (hasExtraEndActions ||
      radioButtonLocation == MiuixRadioButtonLocation.end) {
    endActionsWithRadioButton = <Widget>[
      if (hasExtraEndActions)
        Flexible(
          fit: FlexFit.loose,
          flex: 1,
          child: Padding(
            padding: const EdgeInsetsDirectional.only(end: 8),
            child: Row(
              mainAxisSize: MainAxisSize.min,
              children: endActions!,
            ),
          ),
        ),
      if (radioButtonLocation == MiuixRadioButtonLocation.end)
        radioButtonWidget,
    ];
  } else {
    endActionsWithRadioButton = null;
  }

  return MiuixBasicComponent(
    title: title,
    titleColor: effectiveColors.resolveTitleColor(selected),
    summary: summary,
    summaryColor: effectiveColors.resolveSummaryColor(selected),
    startAction: startActionWidget,
    endActions: endActionsWithRadioButton,
    bottomAction: bottomAction,
    insideMargin: insideMargin,
    onClick: interactive ? _tap : null,
    role: MiuixBasicComponentRole.radioButton,
    holdDownState: holdDownState,
    enabled: enabled,
  );
}