在Flutter中显示图像一次

Question

当我在文件中设置图像并以这样的方式设置图像时，Image.assets出现了问题：

flutter: uses-material-design: true assets: - images/facebook.png

以及当我将其放入代码中时：

Center(
    child: Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        Image.asset(
          "images/facebook.png"

        ),
        Text(
          '$_counter',
          style: Theme.of(context).textTheme.display1,
        ),
      ],
    ),
  ),

运行它，效果很好 但是第二次我运行代码时，它没有显示 这是我得到的错误：

  

I / flutter（4784）：BY图像资源服务引起的异常提示   ╞═════════════════════════════════════════════════ ═══我/颤振（   4784）：解析图像时引发了以下断言：   I / flutter（4784）：无法加载资产：AssetManifest.json。 。 。   I / flutter（4784）：＃381 RenderObjectToWidgetElement.mount   （package：flutter / src / widgets / binding.dart：969：5）I / flutter（4784）：

     

382 RenderObjectToWidgetAdapter.attachToRenderTree。 （package：flutter / src / widgets / binding.dart：915：17）I / flutter（

     

4784）：＃383 BuildOwner.buildScope   （package：flutter / src / widgets / framework.dart：2328：19）I / flutter（   4784）：＃384 RenderObjectToWidgetAdapter.attachToRenderTree   （package：flutter / src / widgets / binding.dart：914：13）I / flutter（4784）：

     

385 WidgetsBinding.attachRootWidget（package：flutter / src / widgets / binding.dart：795：7）I / flutter（4784）：

     

386 runApp（package：flutter / src / widgets / binding.dart：845：7）I / flutter（4784）：＃387 main（package：flutter_app / main.dart：4：16）

     

I / flutter（4784）：＃388 _runMainZoned ..（dart：ui / hooks.dart：229：25）I / flutter（   4784）：＃393 _runMainZoned。   （dart：ui / hooks.dart：221：5）I / flutter（4784）：＃394
  _startIsolate。 （dart：isolate-patch / isolate_patch.dart：305：19）I / flutter（4784）：＃395   _RawReceivePortImpl._handleMessage（dart：isolate-patch / isolate_patch.dart：172：12）I / flutter（4784）：   （从dart：async包中删除了7帧）I / flutter（4784）：图像   提供者：AssetImage（捆绑：null，名称：“ images / facebook.png”）   I / flutter（4784）：映像配置：ImageConfiguration（捆绑：   PlatformAssetBundle＃b5447（），devicePixelRatio：1.5，I / flutter（4784）：   区域设置：en_US，textDirection：TextDirection.ltr，平台：android）   I /颤振（4784）：   ══════════════════════════════════════════════════ ══════════════════════════════════════════════════

Answer 1

检查此

assets:
   - images/facebook.png

确保您拥有完全相同的空格

flutter:

[2 whitespaces or 1 tab]assets:
[4 whitespaces or 2 tabs]- images/facebook.png

每个空间都很重要

Answer 2

我的代码：

import 'package:flutter/material.dart';
import 'dart:io';
import 'package:image_picker/image_picker.dart';
void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'myApp'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  File imageFile;
  int _counter = 0;
  Color red = Colors.red;
   _incrementCounter() async{
     var picture = await ImagePicker.pickImage(source: ImageSource.camera);

    this.setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      imageFile = picture;
      _counter++;
      print("work");
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Image.asset(
              "images/facebook.png"

            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

我的pubspec.yaml：

name: flutter_app
description: A new Flutter application.

# 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: ">=2.1.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter
  image_picker:


  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^0.1.2

dev_dependencies:
  flutter_test:
    sdk: flutter


# 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.
flutter:
  uses-material-design: true
  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

Answer 3

请确保您在pubspec.yaml中使用2或4个空格（避免使用制表符）作为缩进。

您的pubspec.yaml必须是这样

flutter:
  uses-material-design: true
  assets:
    - images/facebook.png

不喜欢

flutter:
  uses-material-design: true
  assets:
      - images/facebook.png # error

或这样

flutter:
  uses-material-design: true
  assets:
  - images/facebook.png # also error

运行
flutter clean
flutter pub get
在您的终端中

Answer 4

1）。创建名为images的文件夹 2）。添加要添加的图像 3）。像这样在pubspec中添加 资产：   -images / xyz.png 4）点击Package得到 5）运行该应用程序（先杀死应用程序并运行）。

Answer 5

这个问题最近发生在我身上。正如@Mohamed Adel回答的那样，您必须保留适当的空格。 您还可以包含整个文件夹eg: images

flutter:

[2 whitespaces]assets:
[4 whitespaces]- images/

如果images文件夹包含子文件夹eg: images/products/

flutter:

[2 whitespaces]assets:
[4 whitespaces]- images/products

在pubspec.yaml中，使用空格比制表符总是安全的

Answer 6

步骤1： -创建一个名为资产的目录，如下所示。并将图像添加到此目录。

第2步：

-将您的目录添加到pubspec.yaml。这支持该目录的所有图像。

第3步：

-在终端上运行此命令。

flutter pub get

第4步：

-编写这样的代码。如果要控制图像大小，请使用height和width属性。

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Image.asset("assets/facebook.png"),
      ),
    );
  }
}

结果：