Flutter 使用Dart（颤振）为我的应用程序创建屏幕截图按钮的问题

我正试图捕获小部件的屏幕截图并将其保存到手机图库中，但它给我的错误如下。我需要帮助>您可以复制粘贴运行下面的完整代码
您需要权限

写入外部存储


步骤1：在
AndroidManifest.xml
中添加权限

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

工作演示


完整代码

import 'dart:io';
import 'dart:typed_data';

import 'package:flutter/material.dart';
import 'package:screenshot/screenshot.dart';
import 'package:image_gallery_saver/image_gallery_saver.dart';
import 'package:simple_permissions/simple_permissions.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: 'Screenshot Demo Home Page'),
    );
  }
}

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

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  File _imageFile;
  bool _allowWriteFile = false;

  //Create an instance of ScreenshotController
  ScreenshotController screenshotController = ScreenshotController();

  void _incrementCounter() {
    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.
      _counter++;
    });
  }

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

  _requestWritePermission() async {
    PermissionStatus permissionStatus = await SimplePermissions.requestPermission(Permission.WriteExternalStorage);

    if (permissionStatus == PermissionStatus.authorized) {
      setState(() {
        _allowWriteFile = true;
      });
    }
  }

  @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: Container(
        child: new Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Screenshot(
                controller: screenshotController,
                child: Column(
                  children: <Widget>[
                    Text(
                      'You have pushed the button this many times:' +
                          _counter.toString(),
                    ),
                    FlutterLogo(),
                  ],
                ),
              ),
              _imageFile != null ? Image.file(_imageFile) : Container(),
            ],
          ),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          _incrementCounter();
          _imageFile = null;
          screenshotController
              .capture(delay: Duration(seconds: 3))
              .then((File image) async {
            print("image path  ${image.path}");
            setState(() {
              _imageFile = image;
            });
            final result =
            await ImageGallerySaver.saveImage(image.readAsBytesSync());
            print("File Saved to Gallery");
          }).catchError((onError) {
            print(onError);
          });
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }

  _saved(File image) async {
    final result = await ImageGallerySaver.saveImage(image.readAsBytesSync());
    print("File Saved to Gallery");
  }
}

导入'dart:io'；
导入“dart:键入的_数据”；
进口“包装：颤振/材料.省道”；
导入“package:screenshot/screenshot.dart”；
导入“package:image_gallery_saver/image_gallery_saver.dart”；
导入“package:simple_permissions/simple_permissions.dart”；
void main（）=>runApp（MyApp（））；
类MyApp扩展了无状态小部件{
//此小部件是应用程序的根。
@凌驾
小部件构建（构建上下文）{
返回材料PP(
标题：“颤振演示”，
主题：主题数据(
//这是应用程序的主题。
//
//尝试使用“flutter run”运行应用程序。您将看到
//应用程序有一个蓝色工具栏。然后，在不退出应用程序的情况下，重试
//将下面的primarySwatch更改为Colors.green，然后调用
//“热重新加载”（在运行“颤振运行”的控制台中按“r”，
//或者只需将更改保存到颤振IDE中的“热重新加载”。
//请注意，计数器没有重置回零；应用程序
//未重新启动。
主样本：颜色。蓝色，
),
主页：MyHomePage（标题：“截图演示主页”），
);
}
}
类MyHomePage扩展StatefulWidget{
MyHomePage（{Key，this.title}）：超级（Key:Key）；
//此小部件是应用程序的主页。它是有状态的，表示
//它有一个状态对象（定义如下），其中包含影响
//看起来怎么样。
//此类是状态的配置。它保存值（在此
//案例名称）由家长（在本例中为应用程序小部件）提供，以及
//由State的build方法使用。小部件子类中的字段包括
//始终标记为“最终”。
最后的字符串标题；
@凌驾
_MyHomePageState createState（）=>\u MyHomePageState（）；
}
类_MyHomePageState扩展状态{
int _计数器=0；
文件imageFile；
bool\u allowWriteFile=false；
//创建ScreenshotController的实例
ScreenshotController ScreenshotController=ScreenshotController（）；
void _incrementCounter（）{
设置状态（）{
//这个对setState的调用告诉颤振框架，某些东西
//已在此状态下更改，这将导致它重新运行下面的生成方法
//以便显示能够反映更新的值。如果我们更改
//_计数器，而不调用setState（），则生成方法将不可用
//再打一次电话，似乎什么也没发生。
_计数器++；
});
}
@凌驾
void initState（）{
super.initState（）；
_requestWritePermission（）；
}
_requestWritePermission（）异步{
PermissionStatus PermissionStatus=等待SimplePermissions.requestPermission（Permission.WriteExternalStorage）；
if（permissionStatus==permissionStatus.authorized）{
设置状态（）{
_allowWriteFile=true；
});
}
}
@凌驾
小部件构建（构建上下文）{
//每次调用setState时都会重新运行此方法，例如，按done
//通过上面的_incrementCounter方法。
//
//对颤振框架进行了优化，以制定重新运行的构建方法
//快速，这样你就可以重建任何需要更新的东西
//而不是必须单独更改小部件的实例。
返回脚手架(
appBar:appBar(
//在这里，我们从MyHomePage对象中获取由创建的值
//使用App.build方法，并使用它设置appbar标题。
标题：文本（widget.title），
),
主体：容器(
孩子：新中心(
子：列(
mainAxisAlignment:mainAxisAlignment.center，
儿童：[
截图(
控制器：屏幕快照控制器，
子：列(
儿童：[
正文(
“你已经按下按钮这么多次了：”+
_counter.toString（），
),
徽标（），
],
),
),
_imageFile！=null？Image.file（_imageFile）：Container（），
],
),
),
),
浮动操作按钮：浮动操作按钮(
已按下：（）{
_递增计数器（）；
_imageFile=null；
屏幕快照控制器
.捕获（延迟：持续时间（秒：3））
.then（（文件映像）异步{
打印（“图像路径${image.path}”）；
设置状态（）{
_图像文件=图像；
});
最终结果=
等待ImageGallerySaver.saveImage（image.readAsBytesSync（））；
打印（“保存到图库的文件”）；
}).catchError（（onError）{
打印（onError）；
});
},
工具提示：“增量”，
子：图标（Icons.add），
)，//此尾随逗号使生成方法的自动格式设置更方便。
);
}
_已保存（文件映像）异步{
最终结果=等待ImageGallerySaver.saveImage（image.readAsBytesSync（））；
打印（“保存到图库的文件”）；
}
}
您可以复制粘贴运行下面的完整代码

您需要权限
写入外部存储


步骤1：在
AndroidManifest.xml
中添加权限

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

工作演示


完整代码

import 'dart:io';
import 'dart:typed_data';

import 'package:flutter/material.dart';
import 'package:screenshot/screenshot.dart';
import 'package:image_gallery_saver/image_gallery_saver.dart';
import 'package:simple_permissions/simple_permissions.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: 'Screenshot Demo Home Page'),
    );
  }
}

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

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  File _imageFile;
  bool _allowWriteFile = false;

  //Create an instance of ScreenshotController
  ScreenshotController screenshotController = ScreenshotController();

  void _incrementCounter() {
    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.
      _counter++;
    });
  }

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

  _requestWritePermission() async {
    PermissionStatus permissionStatus = await SimplePermissions.requestPermission(Permission.WriteExternalStorage);

    if (permissionStatus == PermissionStatus.authorized) {
      setState(() {
        _allowWriteFile = true;
      });
    }
  }

  @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: Container(
        child: new Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Screenshot(
                controller: screenshotController,
                child: Column(
                  children: <Widget>[
                    Text(
                      'You have pushed the button this many times:' +
                          _counter.toString(),
                    ),
                    FlutterLogo(),
                  ],
                ),
              ),
              _imageFile != null ? Image.file(_imageFile) : Container(),
            ],
          ),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          _incrementCounter();
          _imageFile = null;
          screenshotController
              .capture(delay: Duration(seconds: 3))
              .then((File image) async {
            print("image path  ${image.path}");
            setState(() {
              _imageFile = image;
            });
            final result =
            await ImageGallerySaver.saveImage(image.readAsBytesSync());
            print("File Saved to Gallery");
          }).catchError((onError) {
            print(onError);
          });
        },
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }

  _saved(File image) async {
    final result = await ImageGallerySaver.saveImage(image.readAsBytesSync());
    print("File Saved to Gallery");
  }
}

导入'dart:io'；
导入“dart:键入的_数据”；
进口“包装：颤振/材料.省道”；
导入“package:screenshot/screenshot.dart”；
导入“package:image_gallery_saver/image_gallery_saver.dart”；
“导入”包：简单权限/s