Flutter 将圆形遮罩到容器中 [英] Flutter mask a circle into a container

问题描述

我想在容器上添加圆形效果，但我希望圆形不会扩展容器的尺寸，而是被它剪裁.这就是我想要实现的目标:

I want to add a circle effect over a container, but I want the circle to not extend the dimensions of the container, but instead get clipped by it. This is what I'm trying to achieve:

正如您所看到的，白色圆圈自然会延伸红色容器，但相反，我试图让它留在边界内.我该怎么做?

As you can see the white circle naturally would extend the red container but instead, I'm trying to make it stay into the borders. How can I do it?

推荐答案

最简单的方法是使用重叠和剪辑矩形.

The simplest way to do this is to using an overlap and cliprect.

class OverlapSquare extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      height: 200,
      decoration: BoxDecoration(
        borderRadius: BorderRadius.circular(10),
        color: Colors.red,
      ),
      child: ClipRect(
        clipBehavior: Clip.hardEdge,
        child: OverflowBox(
          maxHeight: 250,
          maxWidth: 250,
          child: Center(
            child: Container(
              decoration: BoxDecoration(
                color: Colors.white,
                shape: BoxShape.circle,
              ),
            ),
          ),
        ),
      ),
    );
  }
}

OverFlowBox 允许圆在其父级边界之外绘制，然后 cliprect 将其切回边缘.

The OverFlowBox allows the circle to draw outside the bounds of its parent, and then the cliprect cuts it back to the edge.

仅供参考 - 在我的设备上，我在顶部看到一条细小的红线 &白色圆圈的底部.我很确定这是最近在颤振中引入的错误，因为如果我在容器周围放置白色边框，我也会看到类似的东西.为此，我在 github 上提出了 一个问题.

Just an FYI - on my device I'm getting a tiny red line at the top & bottom of the white circle. I'm fairly sure that's a recently-introduced bug in flutter as I'm also seeing something similar if I put a white border around the container. I've raised an issue on github for that.

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