如何在Flutter中将父小部件的高度传递给子小部件？

Question

我正在尝试从Flutter中的父部件传递堆栈的高度，但我无法做到。请帮助我找到解决方案，我将把我的代码作为参考。

父小工具

  @override
  Widget build(BuildContext context) {
    return  SingleChildScrollView(
      child: Stack(
        children: [

          Picturebackground(//pass Stack height ),

          Center(
            child: Column(
              mainAxisSize: MainAxisSize.max,
              crossAxisAlignment: CrossAxisAlignment.center,
              children: <Widget>[
                Text('varying text'),
              ],
            ),
          ),
        ],
      ),
    );
  }

子部件

dynamic listImagesnotFound = ['assets/svg1.svg','assets/svg2.svg','assets/svg3.svg','assets/svg4.svg'];
Random rnd;

class Picturebackground extends StatelessWidget {
  final double stack_height;
  Picturebackground ({Key key, this.stack_height}) : super(key: key);

  Widget build(BuildContext context) {
    int min = 0;
    int max = listImagesnotFound.length - 1;
    rnd = new Random();
    int r = min + rnd.nextInt(max - min);
    String image_name = listImagesnotFound[r].toString();
    return SvgPicture.asset(image_name,
      fit: BoxFit.cover,
      width: MediaQuery.of(context).size.width,
      height: // get the height of the Stack
    );
  }
}

如何将堆栈的高度传递给SVGPicture。

Answer 1

可以使用LayoutBuilder获取PictureBackground小部件的约束：

dynamic listImagesnotFound = ['assets/svg1.svg','assets/svg2.svg','assets/svg3.svg','assets/svg4.svg'];
Random rnd;

class Picturebackground extends StatelessWidget {
  Widget build(BuildContext context) {
    int min = 0;
    int max = listImagesnotFound.length - 1;
    rnd = new Random();
    int r = min + rnd.nextInt(max - min);
    String image_name = listImagesnotFound[r].toString();

    return LayoutBuilder(
      builder: (context, constraints) {
        // get here
        final height = constraints.maxHeight;

        return SvgPicture.asset(image_name,
          fit: BoxFit.cover,
          width: MediaQuery.of(context).size.width,
          height: height // use here
        );
      }
    );
  }
}