如何在flutter中使用rootBundle加载图片？

Question

我使用图像插件 (image: ^2.0.4)，所以我可以在图像上写一些东西，然后将新图像保存到设备或通过邮件发送。我尝试使用“new File”加载图像，但在 Flutter 上出现错误。我询问并搜索并得到提示，我可以使用 rootBundle 在 Flutter 中加载图像。我做到了，我得到了以下错误。

[ERROR:topaz/lib/tonic/logging/dart_error.cc(16)] 未处理的异常： 无法加载资产：packages/myAppName/assets/images/ReceiptRaw_1.jpg

当我创建一个简单的 dart 控制台应用程序时，该插件可以工作，但无法使用颤振加载。请帮忙，

这是 Flutter 代码：

    Future<bool> makeReceiptImage() async {

// UPDATE ****************************************

      // load the receipt jpeg
  var imageData = await rootBundle.load('packages/myAppName/dekonts/ReceiptRaw_1.jpg');
  print("imageData: $imageData"); // Prints as imageData: Instance of 
'_ByteDataView'

// UPDATE ****************************************

  Image _receiptImage = await decodeImage(new File(imageData).readAsBytesSync());

      drawString(_receiptImage, arial_48, 440, 30, “Customer Name”, color: 0xFF000000); 

      // Write it to disk as a different jpeg 
      var new_jpeg = await encodeJpg(_receiptImage); 
      String newImagePath = await rootBundle.loadString('packages/myAppName/assets/images/ReceiptRaw_2.jpg'); 
      await new File(‘$newImagePath’).writeAsBytesSync(new_jpeg); 
    }

这是 Dart 控制台代码：

import 'dart:io';
import 'dart:convert';
import 'dart:async';
import 'package:image/image.dart';

void main() async {
  // load the receipt jpeg
  String mImagePath = 'images/ReceiptRaw_1.jpg';
  Image _receiptImage = decodeImage(new File(mImagePath).readAsBytesSync());
  drawString(_receiptImage, arial_48, 440, 30, “Customer Name”, color: 0xFF000000);

  // Write it to disk as a different jpeg
  var new_jpeg = encodeJpg(_receiptImage);
  new File('images/ReceiptRaw_1.jpg').writeAsBytesSync(new_jpeg);
}

更新 1： 当我使用下面的代码时，我收到以下错误：

在 pubspec.yaml 中检测到错误： 找不到资产的文件或变体：packages/myAppName/assets/images/ReceiptRaw_1.jpg

 String imageData = await rootBundle.loadString('packages/myAppName/assets/images/ReceiptRaw_1.jpg');
  Image _receiptImage = await decodeImage(new File(imageData).readAsBytesSync());

更新 2： 如果我使用rootBundle.load，则会出现以下错误。

错误：“dart.typed_data::ByteData”类型的值无法分配给“dart.core::String”类型的变量。

var imageData = await rootBundle.load('packages/myAppName/assets/images/ReceiptRaw_1.jpg');
  Image _receiptImage = await decodeImage(new File(imageData).readAsBytesSync());

新更新：

第 1 步： 移动到ReceiptRaw_1.jpg 进入lib/dekonts/ 文件夹

改为：

assets:
  - packages/myAppName/dekonts/ReceiptRaw_1.jpg

改为：

var imageData = await rootBundle.load('packages/myAppName/dekonts/ReceiptRaw_1.jpg');
print("imageData: $imageData"); 

结果： 打印为

imageData：“_ByteDataView”的实例

第 2 步： 移动到 /lib/assets/images/ReceiptRaw_1.jpg 文件夹

改为：

assets:
  - packages/myAppName/lib/assets/images/ReceiptRaw_1.jpg

改为：

var imageData = await rootBundle.load('packages/myAppName/lib/assets/images/ReceiptRaw_1.jpg');
print("imageData: $imageData"); 

结果：错误如下：

解决依赖关系... 运行“gradlew assembleDebug”... 在 pubspec.yaml 中检测到错误： 未找到资产的文件或变体：packages/myAppName/lib/assets/images/ReceiptRaw_1.jpg

更新：

/// 要包括第一张图片，应用程序的pubspec.yaml 应该
/// 在资产部分指定它：
///
/// 资产： /// - 包/fancy_backgrounds/backgrounds/background1.png ///
/// lib/ 是隐含的，因此它不应包含在资产路径中。

Answer 1

pub 依赖的文件不能作为文件使用。它们包含在存档文件中。

将图片添加到pubspec.yaml中的资产

flutter:
  assets:
    - packages/myAppName/assets/images/ReceiptRaw_1.jpg

然后加载它

var imageData = await rootBundle.load('packages/myAppName/assets/images/ReceiptRaw_1.jpg');

为此，文件ReceiptRaw_1.jpg 需要在

myAppName/lib/assets/images/ReceiptRaw_1.jpg

lib/ 部分是强制性的。

Answer 2

在@Günter Zöchbauer 的帮助下，我终于成功了。我对 Stack Overflow 成员的小小贡献。

// TODO: 1 - 加载所有内容

  Future _loadEverything() async {
    await _requestAppDocumentsDirectory();   // TODO: 2 - GET APP DOCUMENTS DIRECTORY
    _dekontExist = await makeReceiptImage(); // TODO: 3 - MAKE A RECEIPT

    // Show the writen image
    if (_dekontExist == true) {
      setState(() {
        newDekontImage = _appDocumentsDirectory + "/" + widget._currentUserReceiptNo + ".jpg";
        imageOkay = true; // FOR - 4 - MAIN WIDGET BUILD
      });
    }
  }

// TODO: 2 - 获取应用文档目录

Future _requestAppDocumentsDirectory() async {
  // I choose temp dir because I don’t want to write twice same Receipt
  // Also when user close the app it will destroys the images
  final _directory =
      await getTemporaryDirectory(); //getApplicationDocumentsDirectory();
  setState(() {
    _appDocumentsDirectory = _directory.path;
  });
}

// TODO: 3 - 制作收据

Future<bool> makeReceiptImage() async {

  // I use this as a template:
  // 'packages/mayApp/assets/images/CapitalReceipt.jpg'  

  ByteData imageData = await rootBundle.load('packages/mayApp/assets/images/CapitalReceipt.jpg');
  List<int> bytes = Uint8List.view(imageData.buffer);
  Image _receiptImage = decodeImage(bytes);

  // TODO: WRITE ON TO THE IMAGE
  drawString(_receiptImage, arial_48, 440, 30, “Customer Receipt - Customer Name”, color: 0xFF000000);


  // Write it to disk as a different jpeg
    var new_jpeg = await encodeJpg(_receiptImage);
    String newDekontImage = _appDocumentsDirectory + "/" + "${_currentUserReceiptNo}" + ".jpg";
    await new File(newDekontImage).writeAsBytesSync(new_jpeg);

  return true;
}

// TODO: 4 - 主要小部件构建

  @override
  Widget build(BuildContext context) {
    capitalHeight = MediaQuery.of(context).size.height;
    capitalWidth = MediaQuery.of(context).size.width;

    if (imageOkay == true) {
      return new Scaffold(
        resizeToAvoidBottomPadding: true,
        appBar: new AppBar(
          title: new Text("Customer Receipt"),
          backgroundColor: const Color(0xFF7CB342),
          elevation: 0.0,
          actions: <Widget>[
            new Container(
              padding: EdgeInsets.only(right: 10.0),
              child: new Icon(Icons.mail),
            )
          ],
        ),
        body: new Column(
          children: <Widget>[
            new Padding(
              padding: EdgeInsets.fromLTRB(0.0, 0.0, 0.0, 0.0),
              child: new Center(
                child: new Container(
                  width: capitalWidth,
                  height: capitalHeight / 2.3,
                  color: Colors.black54, //capitalLightGreen,
                  child: new Container(
                    width: capitalWidth - 20.0,
                    height: capitalHeight / 2.3,
                    child: Image.file(File('$newDekontImage')),
                  )
                ),
              )
            ),
          ],
        ),
      );
    } else {
      return new Scaffold(
          resizeToAvoidBottomPadding: true,
          appBar: new AppBar(
            title: new Text("Customer Receipt"),
            backgroundColor: const Color(0xFF7CB342),
            elevation: 0.0,
            actions: <Widget>[
              new Container(
                padding: EdgeInsets.only(right: 10.0),
                child: new Icon(Icons.mail),
              )
            ],
          ),
          body: new Center(
            child: new CircularProgressIndicator(),
          ));
    }
  }