无法在 flutter 应用程序中加载资产图像

Question

我正在尝试制作一个可以为我掷骰子的应用程序，并遵循相同的教程。看起来教程很旧，这就是我收到错误的原因。该错误将我带到 image_provider.dart 页面，上面写着

<----------------

@protected
  Future<ui.Codec> _loadAsync(AssetBundleImageKey key, DecoderCallback decode) async {

    ByteData? data;
    // Hot reload/restart could change whether an asset bundle or key in a
    // bundle are available, or if it is a network backed bundle.
    try {
      data = await key.bundle.load(key.name);
    } on FlutterError {
      PaintingBinding.instance.imageCache.evict(key);
      rethrow;
    }
    if (data == null) {
      PaintingBinding.instance.imageCache.evict(key);
      throw StateError('Unable to read data');
    }
    return decode(data.buffer.asUint8List());
  }
}
                  ---------->

在模拟器中我看不到图像。

import 'package:flutter/material.dart';


import 'homepage.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Dice Roller',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.green,
      ),
      home: HomePage(),
    );
  }
}

这是homepage.dart

import 'dart:math';

import 'package:flutter/material.dart';

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  AssetImage one = const AssetImage("images/one.png");
  AssetImage two = const AssetImage("images/two.png");
  AssetImage three = const AssetImage("images/three.png");
  AssetImage four = const AssetImage("images/four.png");
  AssetImage five = const AssetImage("images/five.png");
  AssetImage six = const AssetImage("images/six.png");

  AssetImage? diceImage;

  @override
  void initState() {
    super.initState();
    setState(() {
      diceImage = one;
    });
  }

  void rollDice() {
    int rnd = 1 + (Random().nextInt(6));

    AssetImage? newImage;

    switch (rnd) {
      case 1:
        newImage = one;
        break;
      case 2:
        newImage = two;
        break;
      case 3:
        newImage = three;
        break;
      case 4:
        newImage = four;
        break;
      case 5:
        newImage = five;
        break;
      case 6:
        newImage = six;
        break;
    }
    setState(() {
      diceImage = newImage;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Dice Roller'),
      ),
      body: Container(
        child: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Image(
                image: AssetImage('$diceImage'),
                width: 200.0,
                height: 200.0,
              ),
              Container(
                margin: const EdgeInsets.only(top: 100.0),
                child: ElevatedButton(
                  onPressed: rollDice,
                  child: const Text("Roll The Dice!!"),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

这是pubsec.yaml

name: diceroller
description: A new Flutter project.

# The following line prevents the package from being accidentally published to
# pub.dev using `flutter pub publish`. This is preferred for private packages.
publish_to: "none" # Remove this line if you wish to publish to pub.dev

# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# In Android, build-name is used as versionName while build-number used as versionCode.
# Read more about Android versioning at https://developer.android.com/studio/publish/versioning
# In iOS, build-name is used as CFBundleShortVersionString while build-number used as CFBundleVersion.
# Read more about iOS versioning at
# https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
version: 1.0.0+1

environment:
  sdk: ">=2.17.0 <3.0.0"

# Dependencies specify other packages that your package needs in order to work.
# To automatically upgrade your package dependencies to the latest versions
# consider running `flutter pub upgrade --major-versions`. Alternatively,
# dependencies can be manually updated by changing the version numbers below to
# the latest version available on pub.dev. To see which dependencies have newer
# versions available, run `flutter pub outdated`.
dependencies:
  flutter:
    sdk: flutter

  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^1.0.2

dev_dependencies:
  flutter_test:
    sdk: flutter

  # The "flutter_lints" package below contains a set of recommended lints to
  # encourage good coding practices. The lint set provided by the package is
  # activated in the `analysis_options.yaml` file located at the root of your
  # package. See that file for information about deactivating specific lint
  # rules and activating additional ones.
  flutter_lints: ^2.0.0

# For information on the generic Dart part of this file, see the
# following page: https://dart.dev/tools/pub/pubspec

# The following section is specific to Flutter packages.
flutter:
  # The following line ensures that the Material Icons font is
  # included with your application, so that you can use the icons in
  # the material Icons class.
  uses-material-design: true

  # To add assets to your application, add an assets section, like this:
  assets:
    - images/

  # An image asset can refer to one or more resolution-specific "variants", see
  # https://flutter.dev/assets-and-images/#resolution-aware

  # For details regarding adding assets from package dependencies, see
  # https://flutter.dev/assets-and-images/#from-packages

  # To add custom fonts to your application, add a fonts section here,
  # in this "flutter" section. Each entry in this list should have a
  # "family" key with the font family name, and a "fonts" key with a
  # list giving the asset and other descriptors for the font. For
  # example:
  # fonts:
  #   - family: Schyler
  #     fonts:
  #       - asset: fonts/Schyler-Regular.ttf
  #       - asset: fonts/Schyler-Italic.ttf
  #         style: italic
  #   - family: Trajan Pro
  #     fonts:
  #       - asset: fonts/TrajanPro.ttf
  #       - asset: fonts/TrajanPro_Bold.ttf
  #         weight: 700
  #
  # For details regarding fonts from package dependencies,
  # see https://flutter.dev/custom-fonts/#from-packages

调试控制台显示无法加载资产：AssetImage(bundle: null, name: "images/one.png")

Answer 1

出现此错误的原因可能有以下任何一种：

1- 图片名称拼写错误 2- 提供的图片路径错误（指定位置不存在图片） 3- pubspec.yaml 文件

中的资产缩进错误

enter image description here

Answer 2

以下代码仅在 one.png 位于图像目录中时有效。如果任何其他目录包含图像目录，则需要在 pubspec.yaml.

中实现它

试试这个并确认。

Image(
                image: AssetImage("images/one.png"),
                width: 200.0,
                height: 200.0,
              ),

如果可行，您需要检查 $diceImage

的值

试试这个。

Image(
                image: diceImage,
                width: 200.0,
                height: 200.0,
              ),

Answer 3

diceImage 已经是 AssetImage.

Image(
  image: diceImage,
  width: 200.0,
  height: 200.0,
),

Answer 4

这里直接赋值AssetImage

 AssetImage? diceImage;

  @override
  void initState() {
    super.initState();
    setState(() {
      diceImage = one;
    });
  }

所以我相信你应该像这样使用它，

 children: <Widget>[
              Image(
                image: diceImage,
                width: 200.0,
                height: 200.0,
              ),
              Container(
                margin: const EdgeInsets.only(top: 100.0),
                child: ElevatedButton(
                  onPressed: rollDice,
                  child: const Text("Roll The Dice!!"),
                ),
              ),
            ],

无法在 flutter 应用程序中加载资产图像

Unable to load asset image in the flutter app

dart

flutter