Flutter：断言失败：第 1927 行 pos 12：\'hasSize\'答案

【问题标题】：Flutter: Failed assertion: line 1927 pos 12: 'hasSize'Flutter：断言失败：第 1927 行 pos 12：\'hasSize\'
【发布时间】：2023-01-24 01:53:34
【问题描述】：

我想在背景中添加图像。我在 StackOverflow 中找到了这段代码 sn-p。

SizedBox.expand(
        // -> 01
        child: Container(
          decoration: BoxDecoration(
            image: DecorationImage(
              image: NetworkImage(
                  'https://wallpapercave.com/wp/wp5561184.jpg'),
              fit: BoxFit.cover, // -> 02
            ),
          ),
        ),
      ),

这在这段代码中对我来说效果很好：

enter codeimport 'package:flutter/material.dart';

class Welcome extends StatelessWidget {
  final int _picState;

  final VoidCallback _picStateChange;

  final Function _quizStarted;

  Welcome(this._quizStarted, this._picState, this._picStateChange);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        alignment: AlignmentDirectional.bottomCenter,
        children: [
          SizedBox.expand(
            // -> 01
            child: Container(
              decoration: BoxDecoration(
                image: DecorationImage(
                  image: NetworkImage(
                      'https://wallpapercave.com/wp/wp5561184.jpg'),
                  fit: BoxFit.cover, // -> 02
                ),
              ),
            ),
          ),
          SafeArea(
              child: Padding(
            padding: const EdgeInsets.symmetric(horizontal: 20),
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                const Spacer(),
                Text(
                  'Start Application',
                  style: Theme.of(context).textTheme.headline3?.copyWith(
                        color: Colors.white54,
                        fontWeight: FontWeight.bold,
                      ),
                  textAlign: TextAlign.center,
                ),
                Spacer(),
                Spacer(),
                TextField(
                  onTap: () => _picStateChange(),
                  decoration: InputDecoration(
                    focusColor: Colors.amber,
                    filled: true,
                    fillColor: Colors.white.withOpacity(0.2),
                    hintText: 'ENTER YOUR NAME HERE',
                    hintStyle: TextStyle(
                        wordSpacing: 2,
                        fontWeight: FontWeight.bold,
                        color: Colors.white,
                        decoration: TextDecoration.underline),
                    border: OutlineInputBorder(
                        borderRadius: BorderRadius.all(Radius.circular(12))),
                  ),
                ),
                InkWell(
                  onTap: () => _quizStarted(),
                  child: Container(
                    width: double.infinity,
                    alignment: Alignment.center,
                    padding: EdgeInsets.all(15),
                    decoration: BoxDecoration(
                        borderRadius: BorderRadius.all(Radius.circular(20)),
                        gradient: (LinearGradient(
                            colors: [Colors.lime, Colors.blueGrey.shade700],
                            begin: Alignment.topRight,
                            end: Alignment.bottomLeft))),
                    child: Text('START THE APPLICATION',
                        style: Theme.of(context)
                            .textTheme
                            .button
                            ?.copyWith(color: Colors.white38)),
                  ),
                ),
                Spacer(),
              ],
            ),
          ))
        ],
      ),
    );
  }
}

但是当我在另一部分（下面的部分）中使用相同的代码时，错误“断言失败：第 1927 行第 12 行：'hasSize'“出现

**import 'package:flutter/material.dart';

class Answer extends StatelessWidget {
  final VoidCallback ansk;
  final String gimme_Da_Answer;

  Answer(this.ansk, this.gimme_Da_Answer);
  @override
  Widget build(BuildContext context) {
    return Stack(
        alignment: AlignmentDirectional.bottomCenter,
        children: [
          SizedBox.expand(
            // -> 01
            child: Container(
              decoration: BoxDecoration(
                image: DecorationImage(
                  image: NetworkImage(
                      'https://wallpapercave.com/wp/wp5561184.jpg'),
                  fit: BoxFit.fitHeight, // -> 02
                ),
              ),
            ),
          ),
          SafeArea(
            child: Padding(
              padding: const EdgeInsets.symmetric(vertical: 18, horizontal: 17),
              child: InkWell(
                onTap: () => ansk(),
                child: (Container(
                  child: Text(gimme_Da_Answer,textAlign: TextAlign.center,
                      style: TextStyle(
                        
                          fontSize: 25,
                          color: Colors.cyan.shade800,
                          fontWeight: FontWeight.bold)),
                  width: double.infinity,
                  padding: EdgeInsets.all(15),
                  margin: EdgeInsets.all(10),
                  decoration: BoxDecoration(
                      border: Border.all(color: Colors.blue, width: 4),
                      color: Colors.blueAccent.shade100.withOpacity(0.4),
                      borderRadius: BorderRadius.all(Radius.circular(15))),
                )),
              ),
            ),
          ),
        ]);
  }
}**

^为我显示错误的代码多谢！！！

【问题讨论】：

用 material 小部件包裹你的堆栈，比如 Scaffold

标签： flutter dart

【解决方案1】：

此处出现错误是因为 Widget 正在寻找尺寸，因为 fit 已在 BoxDecoration 上设置。要解决此问题，请在Container 上设置宽度和高度。

Container(
  // set Container dimension
  width: 100, 
  height: 100,
  decoration: BoxDecoration(
    image: DecorationImage(
      image: NetworkImage(),
      fit: BoxFit.cover,
    ),
  ),
)

【讨论】：