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 ThemeData theme = Theme.of(context);

  // 获取全局主题配置
  final JunnySectionHeaderThemeData? globalTheme =
      JunnyGlobalWidgetConfig.instance.sectionHeaderTheme;

  // 默认装饰：优先使用全局配置，否则使用内置默认值（仅顶部 12.0 圆角）
  final Decoration defaultDecoration = globalTheme?.defaultTitleDecoration ??
      BoxDecoration(
        color: theme.primaryColor,
        borderRadius: const BorderRadius.only(
          topLeft: Radius.circular(12.0),
          topRight: Radius.circular(12.0),
        ),
      );

  // 默认分割线装饰
  final Decoration defaultDividerDecoration = dividerDecoration ??
      globalTheme?.defaultDividerDecoration ??
      BoxDecoration(
        color: dividerColor ??
            globalTheme?.defaultDividerColor ??
            theme.primaryColor,
      );

  // 默认文本样式：优先使用全局配置
  final TextStyle defaultTextStyle = titleTextStyle ??
      globalTheme?.defaultTitleTextStyle ??
      theme.textTheme.bodyMedium?.copyWith(
        color: Colors.white,
        fontWeight: FontWeight.w500,
      ) ??
      const TextStyle(
        color: Colors.white,
        fontWeight: FontWeight.w500,
      );
  // 统一产出 Stack 布局需要的三个关键值，避免标题层和分割线层各自估算后出现错位。
  final ({
    double effectiveDividerHeight,
    double resolvedHeight,
    double titleBottomPosition,
  }) layoutMetrics = _resolveLayoutMetrics(
    context,
    globalTheme: globalTheme,
    defaultTextStyle: defaultTextStyle,
  );

  return Padding(
    padding: margin,
    child: SizedBox(
      height: layoutMetrics.resolvedHeight,
      width: width,
      child: Stack(
        children: <Widget>[
          // 背景分割线层 - 分割线底边贴住标题底边，看起来像从标题自然延伸出去。
          if (showDivider)
            _buildDividerWidget(
              defaultDividerDecoration,
              effectiveDividerHeight: layoutMetrics.effectiveDividerHeight,
              titleBottomPosition: layoutMetrics.titleBottomPosition,
            ),

          // 标题层
          _buildTitleWidget(defaultDecoration, defaultTextStyle),
        ],
      ),
    ),
  );
}