Preface:

I'm using the

Full Traceback:

======== 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)
====================================================================================================

• Why isn't my image being saved to the device when calling _captureAndSaveQRCode()?

Side note:

I recently posted an answer (currently in Bounty) with (almost) the same code as in this question which does work correctly, so, what's the difference?

CodePudding user response：

load image with Image.file(File(imagePath))
Image.Asset is for loading images defined in pubspec.yaml

Edit:
the path in captureAndSave is directory path. it takes another optional argument fileName.

// 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

CodePudding user response：

The problem was that I had an empty setState:

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

So to solve the problem, I removed the setState and also got rid of the _loadImage() function. And then change the image variable within the TextButton():

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

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

Complete working example:

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();
  }
}