错误使用ParentDataWidget。- 怎么修复？

Question

我遇到了错误：父级数据组件的使用不正确。

import 'package:flutter/material.dart';
import 'package:font_awesome_flutter/font_awesome_flutter.dart';
import 'package:testapp/constants.dart';
import 'package:testapp/request/quotation_resources.dart';
import 'dart:math';

class AuctionDetails extends StatelessWidget {
  final QuotationResources quotationResources;

  const AuctionDetails({Key key, this.quotationResources}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: kPrimaryColor,
      appBar: buildAppBar,
      body: BodyAuction(),
    );
  }

  AppBar get buildAppBar {
    return AppBar(
      backgroundColor: kBackgroundColor,
      elevation: 0,
      leading: Padding(
        padding: EdgeInsets.only(left: kDefaultPadding),
        child:
            IconButton(icon: Icon(FontAwesomeIcons.backward), onPressed: () {}),
      ),
    );
  }
}

class BodyAuction extends StatelessWidget {
  final QuotationResources quotationResources;

  const BodyAuction({Key key, this.quotationResources}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    Size size = MediaQuery.of(context).size;
    var cardAspectRatio = 10.0 / 14.0;
    var widgetAspectRatio = cardAspectRatio * 1.2;
    return Column(
      children: <Widget>[
        Container(
          padding: EdgeInsets.symmetric(horizontal: kDefaultPadding),
          decoration: BoxDecoration(
            color: kBackgroundColor,
            borderRadius: BorderRadius.only(
              bottomLeft: Radius.circular(50),
              bottomRight: Radius.circular(50),
            ),
          ),
          child: Column(
            children: <Widget>[
              Container(
                margin: EdgeInsets.symmetric(vertical: kDefaultPadding),
                height: size.width * 0.8,
                child: CardSlider(),
              ),
            ],
          ),
        ),
      ],
    );
  }
}

class CardSlider extends StatefulWidget {
  @override
  _CardSliderState createState() => _CardSliderState();
}

var cardAspectRatio = 10.0 / 14.0;
var widgetAspectRatio = cardAspectRatio * 1.2;

class _CardSliderState extends State<CardSlider> {
  var currentPage = images.length - 1.0;
  @override
  Widget build(BuildContext context) {
    PageController controller = PageController(initialPage: images.length - 1);
    controller.addListener(() {
      setState(() {
        currentPage = controller.page;
      });
    });
    return Column(
      children: <Widget>[
        CardScrollWidget(currentPage),
        Positioned.fill(
          child: PageView.builder(
            itemCount: images.length,
            controller: controller,
            reverse: true,
            itemBuilder: (context, index) {
              return Container();
            },
          ),
        )
      ],
    );
  }
}

class CardScrollWidget extends StatelessWidget {
  var currentPage;
  var padding = 20.0;
  var verticalInset = 20.0;

  CardScrollWidget(this.currentPage);

  @override
  Widget build(BuildContext context) {
    return new AspectRatio(
      aspectRatio: widgetAspectRatio,
      child: LayoutBuilder(builder: (context, contraints) {
        var width = contraints.maxWidth;
        var height = contraints.maxHeight;

        var safeWidth = width - 2 * padding;
        var safeHeight = height - 2 * padding;

        var heightOfPrimaryCard = safeHeight;
        var widthOfPrimaryCard = heightOfPrimaryCard * cardAspectRatio;

        var primaryCardLeft = safeWidth - widthOfPrimaryCard;
        var horizontalInset = primaryCardLeft / 2;

        List<Widget> cardList = new List();

        for (var i = 0; i < images.length; i++) {
          var delta = i - currentPage;
          bool isOnRight = delta > 0;

          var start = padding +
              max(
                  primaryCardLeft -
                      horizontalInset * -delta * (isOnRight ? 15 : 1),
                  0.0);

          var cardItem = Positioned.directional(
            top: padding + verticalInset * max(-delta, 0.0),
            bottom: padding + verticalInset * max(-delta, 0.0),
            start: start,
            textDirection: TextDirection.rtl,
            child: ClipRRect(
              borderRadius: BorderRadius.circular(16.0),
              child: Container(
                decoration: BoxDecoration(color: Colors.white, boxShadow: [
                  BoxShadow(
                      color: Colors.black12,
                      offset: Offset(3.0, 6.0),
                      blurRadius: 10.0)
                ]),
                child: AspectRatio(
                  aspectRatio: cardAspectRatio,
                  child: Stack(
                    fit: StackFit.expand,
                    children: <Widget>[
                      Image.asset(images[i], fit: BoxFit.cover),
                      Align(
                        alignment: Alignment.bottomLeft,
                      )
                    ],
                  ),
                ),
              ),
            ),
          );
          cardList.add(cardItem);
        }
        return Stack(
          children: cardList,
        );
      }),
    );
  }
}

错误代码为：

The following assertion was thrown while applying parent data.:
Incorrect use of ParentDataWidget.

The ParentDataWidget Positioned(left: 0.0, top: 0.0, right: 0.0, bottom: 0.0) wants to apply ParentData of type StackParentData to a RenderObject, which has been set up to accept ParentData of incompatible type FlexParentData.

Usually, this means that the Positioned widget has the wrong ancestor RenderObjectWidget. Typically, Positioned widgets are placed directly inside Stack widgets.
The offending Positioned is currently placed inside a Column widget.

The ownership chain for the RenderObject that received the incompatible parent data was:
  _ScrollSemantics-[GlobalKey#8af92] ← Scrollable ← NotificationListener<ScrollNotification> ← PageView ← Positioned ← Column ← CardSlider ← ConstrainedBox ← Padding ← Container ← ⋯
When the exception was thrown, this was the stack: 
#0      RenderObjectElement._updateParentData.<anonymous closure> (package:flutter/src/widgets/framework.dart:5645:11)
#1      RenderObjectElement._updateParentData (package:flutter/src/widgets/framework.dart:5661:6)
#2      RenderObjectElement.attachRenderObject (package:flutter/src/widgets/framework.dart:5682:7)
#3      RenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5376:5)
#4      SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:5829:11)
...

- MGR DR

Answer 1

错误代码已经展示了问题所在。"定位组件放置在堆栈组件内直接放置。有问题的定位当前放置在列组件内。" 您必须将定位组件放置在堆栈组件内。您不能将它们放置在列中。

Column(
      children: <Widget>[
        CardScrollWidget(currentPage),
        Positioned.fill(
          child: PageView.builder(
            itemCount: images.length,
            controller: controller,
            reverse: true,
            itemBuilder: (context, index) {
              return Container();
            },
          ),
        )
      ],
    );

只需将Column替换为Stack或不使用Positioned.fill即可。

- Quasi