Flutter“屏幕快照软件包：为什么是captureandsave（）`方法将图像保存到我的（Android）设备？

Question

序言：

我正在使用 ScreenShot package。在此软件包中，有一个方法 cartureandsave（）代码>将小部件作为图像保存到特定位置，但是，当我调用此功能时，我的图像没有被保存。为什么？

完整的代码示例：

import 'dart:io';

import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';
import 'package:qr_flutter/qr_flutter.dart';
import 'package:screenshot/screenshot.dart';

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

  @override
  State<QrCodeScreen> createState() => _QrCodeScreenState();
}

class _QrCodeScreenState extends State<QrCodeScreen> {
  final _screenshotController = ScreenshotController();
  Image? image;
  var doesTheImageExist = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          if (image == null)
            TextButton(
              child: Text("Save QR Code"),
              onPressed: () async {
                await _captureAndSaveQRCode();
                image = await _loadImage();
                setState(() {});
              },
            )
          else
            image!,
          Text("Is the QR Code saved to your device? ${doesTheImageExist}"),
          if (image == null)
            Screenshot(
                controller: _screenshotController,
                child: _buildQRImage('_authProvider.user!.uid')),
        ],
      ),
    );
  }

  Widget _buildQRImage(String data) {
    return QrImage(
      data: data,
      size: 250.0,
      gapless: false,
      foregroundColor: Colors.black,
      backgroundColor: Colors.white,
    );
  }

  Future<String> get imagePath async {
    final directory = (await getApplicationDocumentsDirectory()).path;
    return '$directory/qr.png';
  }

  Future<Image> _loadImage() async {
    return imagePath.then((imagePath) => Image.asset(imagePath));
  }

  Future<void> _captureAndSaveQRCode() async {
    final path = await imagePath;
    await _screenshotController.captureAndSave(path);
    // It always returns false, although I'm saving the file using `captureAndSave` .
    doesTheImageExist = File(path).existsSync();
  }
}

问题：

在上面的代码中，当我单击textButton（）时，它说“保存qr code” ，然后调用_CAPTUREANDSAVEQRCRCRCODE（）和_loadimage（）。因此，我的图像应该成功地保存到我的（Android）手机中。但是，我遇到了一个错误：

Unable to load asset: /data/user/0/com.example.qr/app_flutter/qr.png

全追溯：

======== Exception caught by image resource service ================================================
The following assertion was thrown resolving an image codec:
Unable to load asset: /data/user/0/com.example.qr/app_flutter/qr.png

When the exception was thrown, this was the stack: 
#0      PlatformAssetBundle.load (package:flutter/src/services/asset_bundle.dart:237:7)
<asynchronous suspension>
#1      AssetBundleImageProvider._loadAsync (package:flutter/src/painting/image_provider.dart:675:14)
<asynchronous suspension>
Image provider: AssetImage(bundle: null, name: "/data/user/0/com.example.qr/app_flutter/qr.png")
Image key: AssetBundleImageKey(bundle: PlatformAssetBundle#5986d(), name: "/data/user/0/com.example.qr/app_flutter/qr.png", scale: 1.0)
====================================================================================================

• 为什么我的图像在调用时不会保存到设备_CAPTUREANDSAVEQRCODE（）？

---

旁注：

i 最近发布了一个答案（当前在赏金中）（几乎）与此问题相同的代码（几乎）正常工作，那么有什么区别？

Answer 1

问题是我有一个空的setState：

onPressed: () async {
                await _captureAndSaveQRCode();
                image = await _loadImage();
                setState(() {});
              },
            )

为了解决问题，我删除了setState，也摆脱了_loadimage（）>功能。
然后更新image在textButton（）中更新了变量：

  TextButton(
              child: Text("Save QR Code"),
              onPressed: () async {
                await _captureAndSaveQRCode();

                setState(() {
                  doesTheImageExist = true;
                  image = image;
                });
              },
            )

---

完成工作示例：

import 'dart:io';

import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';
import 'package:qr_flutter/qr_flutter.dart';
import 'package:screenshot/screenshot.dart';

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

  @override
  State<QrCodeScreen> createState() => _QrCodeScreenState();
}

class _QrCodeScreenState extends State<QrCodeScreen> {
  final _screenshotController = ScreenshotController();
  Image? image;
  var doesTheImageExist = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          if (image == null)
            TextButton(
              child: Text("Save QR Code"),
              onPressed: () async {
                await _captureAndSaveQRCode();

                setState(() {
                  doesTheImageExist = true;
                  image = image;
                });
              },
            )
          else
            image!,
          Row(children: [
            Text('hi'),
            Text("Is the QR Code saved to your device? ${doesTheImageExist}")
          ]),
          if (image == null)
            Screenshot(
                controller: _screenshotController,
                child: _buildQRImage('_authProvider.user!.uid')),
        ],
      ),
    );
  }

  Widget _buildQRImage(String data) {
    return QrImage(
      data: data,
      size: 250.0,
      gapless: false,
      foregroundColor: Colors.black,
      backgroundColor: Colors.white,
    );
  }

  Future<String> get imagePath async {
    final directory = (await getApplicationDocumentsDirectory()).path;
    return '$directory/qr.png';
  }

  // Future<Image> _loadImage() async {
  //   return imagePath.then((imagePath) => Image.asset(imagePath));
  // }

  Future<void> _captureAndSaveQRCode() async {
    final path = await imagePath;
    await _screenshotController.captureAndSave(path);
    // It always returns false, although I'm saving the file using `captureAndSave` .
    doesTheImageExist = File(path).existsSync();
  }
}

Answer 2

加载图像带有image.file（file（imagepath））
image.asset用于加载pubspec.yaml

编辑中定义的图像：
Caureandsave的路径是目录路径。它需要另一个可选的参数文件名。

// previous code

// i create new getter for directory
Future<String> get dirPath async {
    final directory = (await getApplicationDocumentsDirectory()).path;
    return directory;
  }

  Future<String> get imagePath async {
    final directory = await dirPath;
    return '$directory/qr.png';
  }

  Future<Image> _loadImage() async {
    return imagePath.then((imagePath) => Image.file(File(imagePath)));
  }

  Future<void> _captureAndSaveQRCode() async {
    final path = await dirPath;
    await _screenshotController.captureAndSave(path, fileName: "qr.png");
    // It always returns false, although I'm saving the file using `captureAndSave` .
    doesTheImageExist = File(path).existsSync();
  }

// the rest of the code