每日见闻之Container Decoration

1 Decoation 主要有两个方法

javascript 复制代码

Path getClipPath(Rect rect, TextDirection textDirection) {
  throw UnsupportedError('${objectRuntimeType(this, 'This Decoration subclass')} does not expect to be used for clipping.');
}

less 复制代码

@factory
BoxPainter createBoxPainter([ VoidCallback onChanged ]);

getClipPath 返回的是裁剪的路径，裁剪的是child的显示区域。Rect 就是Container的范围。

createBoxPainter 返回的是自定义绘制内容的BoxPointer

2 BoxPainter主要是实现下面的方法

arduino 复制代码

void paint(Canvas canvas, Offset offset, ImageConfiguration configuration);

offset Container 在父节点中的位置

configuration Container的一些信息，包含宽高

最后留下一个demo，裁剪圆形图片

scala 复制代码

// 自定义装饰：绘制矩形，但裁剪为圆形
class CircleWithRectDecoration extends Decoration {
  final Color color;

  const CircleWithRectDecoration({required this.color});

  @override
  BoxPainter createBoxPainter([VoidCallback? onChanged]) {
    return _CircleWithRectPainter(this, onChanged);
  }

  @override
  Path getClipPath(Rect rect, TextDirection textDirection) {
    // 返回圆形裁剪路径
    return Path()
      ..addRect(Rect.fromCenter(center: rect.center, width: rect.width / 2, height: rect.height/2));
  }
}

class _CircleWithRectPainter extends BoxPainter {
  final CircleWithRectDecoration decoration;

  _CircleWithRectPainter(this.decoration, VoidCallback? onChanged) : super(onChanged);

  @override
  void paint(Canvas canvas, Offset offset, ImageConfiguration configuration) {
    final rect = offset & configuration.size!;
    final paint = Paint()
      ..color = decoration.color
      ..style = PaintingStyle.fill;

    // 绘制矩形（而非圆形）
    canvas.drawOval(rect, paint);
  }
}

使用

less 复制代码

Container(
  width: 150,
  height: 150,
  clipBehavior: Clip.antiAlias, // 启用裁剪
  decoration: const CircleWithRectDecoration(color: Colors.blue),
  // 默认 clipBehavior: Clip.none，getClipPath() 无效
  child: const FlutterLogo(size: 150),
)