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 bool noTint = identical(tint, kMiuixTintUnspecified);
  final Color? resolvedTint =
      noTint ? null : (tint ?? MiuixContentColor.of(context));

  if (icon != null) {
    // Material 的 Icon 已通过 SrcIn 上色、默认 24、并在 semanticLabel 非空时
    // 发出 image 语义，与 miuix Icon.kt 完全一致。
    return Icon(
      icon,
      color: resolvedTint,
      size: size ?? MiuixIconDefaults.defaultSize,
      semanticLabel: contentDescription,
    );
  }

  if (vector != null) {
    // 矢量图标：目标框为显式 size（正方形）或矢量 intrinsic size；
    // FittedBox 把视口坐标系的绘制等比缩放进目标框（ContentScale.Fit）。
    // tint 语义与 Icon.kt 一致：kMiuixTintUnspecified 不上色，否则整幅 SrcIn。
    final Size box =
        size != null ? Size.square(size!) : vector!.intrinsicSize;
    Widget result = SizedBox.fromSize(
      size: box,
      child: FittedBox(
        fit: BoxFit.contain,
        child: SizedBox.fromSize(
          size: vector!.viewport,
          child: CustomPaint(
            size: vector!.viewport,
            painter: MiuixVectorIconPainter(vector!, tint: resolvedTint),
          ),
        ),
      ),
    );
    if (contentDescription != null) {
      result = Semantics(label: contentDescription, image: true, child: result);
    }
    return result;
  }

  // child 路径：任意 Widget（如多色 Image）。
  Widget result = child!;
  if (size != null) {
    // ContentScale.Fit -> BoxFit.contain，仅在显式给尺寸时约束。
    result = SizedBox(
      width: size,
      height: size,
      child: FittedBox(fit: BoxFit.contain, child: result),
    );
  }
  if (!noTint) {
    // ColorFilter.tint(color) 默认 BlendMode.SrcIn。
    result = ColorFiltered(
      colorFilter: ColorFilter.mode(resolvedTint!, BlendMode.srcIn),
      child: result,
    );
  }
  if (contentDescription != null) {
    // Role.Image -> image: true；contentDescription 为 null 时不包裹。
    result = Semantics(label: contentDescription, image: true, child: result);
  }
  return result;
}