类型“List<dynamic>”不是类型“Uint8List”的子类型

Question

我正在使用一个名为的 flutter 插件device_apps来获取安装在我的 Android 设备中的应用程序信息。

List<Application>如果我将对象从应用程序转换为 ，它会返回一个提供图标的图标ApplicationWithIcon。

但它返回的图标是 Uint8 List 类型，我想将其保存在本地并稍后在 Image.memory() 中使用它。

如果我直接使用它而不在本地保存，那么它可以像 Image.memory(app.icon) 一样正常工作。但是当我将图标保存在 json 文件中然后使用它时，它会显示错误：

类型“List”不是类型“Uint8List”的子类型

如何将其保存到本地然后使用？

import 'dart:async';
import 'dart:convert';
import 'dart:ffi';
import 'dart:io';
import 'dart:typed_data';
import 'package:flutter/material.dart';
import 'package:path_provider/path_provider.dart';
import 'package:device_apps/device_apps.dart';
import 'package:app_settings/app_settings.dart';
import 'package:flutter/services.dart' show rootBundle;

void main() {
  runApp(
    MaterialApp(
      title: 'Reading and Writing Files',
      home: MyApp(),
    ),
  );
}

const String dataFile = 'data1.json';

class MyApp extends StatefulWidget {
  @override
  _AppState createState() => _AppState();
}

class _AppState extends State<MyApp> {
  String data;

  File _filePath;
  bool _fileExists = false;
  String jsonString;

  List<dynamic> _json = [];
  List<dynamic> _jsonshow = [];

  List<Application> appsDetail;

  void checkFile() async {
    // chek if file exists
    String dir = (await getApplicationDocumentsDirectory()).path;
    String savePath = '$dir/$dataFile';

//for a directory: await Directory(savePath).exists();
    if (await File(savePath).exists()) {
      print("File exists");
    } else {
      print("File don't exists");
    }
  }

  Future<String> get _localPath async {
    final directory = await getApplicationDocumentsDirectory();
    print(directory.path);
    return directory.path;
  }

  Future<File> get _localFile async {
    final path = await _localPath;
    return File('$path/$dataFile');
  }

  void appDetail() async {
    print("Getting app informations using 'device_apps' : ");
    List<Application> apps = await DeviceApps.getInstalledApplications(
      includeSystemApps: true,
      includeAppIcons: true,
      onlyAppsWithLaunchIntent: true,
    );
    print("Printing apps detail from appDetail() Funtion  apps : ");
    // for (int i = 0; i < apps.length; i++) print(apps[i]);

    print(apps);

    appsDetail = apps;

    for (int i = 0; i < apps.length; i++) {
      ApplicationWithIcon icon = apps[i] as ApplicationWithIcon;

      print(icon.icon.runtimeType);

      // print(apps[i]);
      _json.add({
        "totalApps": apps.length,
        "appName": apps[i].appName,
        "apkFilePath": apps[i].apkFilePath,
        "packageName": apps[i].packageName,
        "versionName": apps[i].versionName,
        "versionCode": apps[i].versionCode,
        "dataDir": apps[i].dataDir,
        "systemApp": apps[i].systemApp,
        "installTimeMillis": apps[i].installTimeMillis,
        "updateTimeMillis": apps[i].updateTimeMillis,
        "icon": icon.icon,

        // "category": apps[i].category
      });
    }

    print(_json);
  }

  void writeJsonfile() async {
    print("Writing json file : ");

    _filePath = await _localFile;

    print("json before encoding : ");
    print("$_json");

    jsonString = jsonEncode(_json);

    print("jsonString after encoding : ");

    print(jsonString);
    _filePath.writeAsString(
      jsonEncode(jsonString),
    );
  }

  Future<List<Object>> Apps() async {
    print("Reading Json file");

    _filePath = await _localFile;
    _fileExists = await _filePath.exists();
    print('0. File exists? $_fileExists');

    if (_fileExists) {
      try {
        String jsonString = await _filePath.readAsString();
        _json = jsonDecode(jsonString);
        print('printing json file after reading : ');
        print(_json);
        return _json;
      } catch (e) {
        // Print exception errors
        print('Tried reading _file error: $e');
        // If encountering an error, return null
      }
    } else {}
  }

  @override
  void initState() {
    super.initState();
    appDetail();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(title: Text('Reading and Writing data')),
        body: Column(
          children: <Widget>[
            IconButton(icon: Icon(Icons.ac_unit), onPressed: Apps),
            _json.length >= 1
                ? GridView.builder(
                    shrinkWrap: true,
                    physics: ScrollPhysics(),
                    scrollDirection: Axis.vertical,
                    itemCount: _json.length,
                    gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
                        crossAxisCount: 5, childAspectRatio: 2.0),
                    itemBuilder: (BuildContext context, int index) {
                      return Column(
                        children: <Widget>[
                          Expanded(child: Text(_json[index]["appName"])),
                          Expanded(child: Image.memory(_json[index]["icon"])),
                        ],
                      );
                    })
                : Text("No Data Found"),
          ],
        ));
  }
}

Answer 1

我在将图像从本机模块（Android）传递到 Flutter 时遇到了同样的问题。（我正在做一个插件）

默认情况下，Flutter 将处理来自底层平台的数据类型并将其映射到 Dart 中的正确数据类型，请在此处查看此表以查看数据类型。但我的情况听起来像是 Flutter 拦截了类型的值byte[]，因此List<dynamic>只需将其从 Flutter 可以处理它的地方强制转换List<dynamic>即可List<Int>。

• 只需复制这个方法并给它你的 List，它就会强制转换 &return Unit8List，它可以在 Flutter 中的任何地方使用，例如image.memory().

  Uint8List _getImageBinary(dynamicList) {
    List<int> intList = dynamicList.cast<int>().toList(); //This is the magical line.
    Uint8List data = Uint8List.fromList(intList);
    return data;
  }