Android '中未定义的类；路径提供程序'；颤振依赖

在添加path_提供程序依赖项后，我遇到了一些未定义某些类的问题。“目录”和“文件”未定义，这个问题是在我尝试在pubspec.yaml中将path_提供程序实现到我的项目后出现的。这是在按下图标按钮时向文本文件添加字符串所必需的

导入：

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:cryptick/data/crypto_data.dart';
import 'package:cryptick/modules/crypto_presenter.dart';
import 'package:shimmer/shimmer.dart';
import 'dart:async';
import 'package:path_provider/path_provider.dart';

ListTile _getListItemUi(Crypto currency, MaterialColor color) {
    return new ListTile(
      leading: new Image.network("http://cryptoicons.co/32@2x/color/"+currency.symbol.toLowerCase()+"@2x.png"),
      title: new Text(currency.name,
          style: new TextStyle(fontWeight: FontWeight.bold)),
      subtitle:
      _getSubtitleText(currency.price_usd, currency.percent_change_1h),
      isThreeLine: true,
      trailing: new IconButton(
        icon: new Icon(Icons.add),
        onPressed: () async { Directory appDocDir = await getApplicationDocumentsDirectory();
        String appDocPath = appDocDir.path;
        new File('$appDocPath/my_file.txt').writeAsStringSync('myVar: $_currencies');  
        }
      ),
    );
  }

onPressed: () async { Directory appDocDir = await getApplicationDocumentsDirectory();

new File('$appDocPath/my_file.txt').writeAsStringSync('myVar: $_currencies');  

问题代码：

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:cryptick/data/crypto_data.dart';
import 'package:cryptick/modules/crypto_presenter.dart';
import 'package:shimmer/shimmer.dart';
import 'dart:async';
import 'package:path_provider/path_provider.dart';

ListTile _getListItemUi(Crypto currency, MaterialColor color) {
    return new ListTile(
      leading: new Image.network("http://cryptoicons.co/32@2x/color/"+currency.symbol.toLowerCase()+"@2x.png"),
      title: new Text(currency.name,
          style: new TextStyle(fontWeight: FontWeight.bold)),
      subtitle:
      _getSubtitleText(currency.price_usd, currency.percent_change_1h),
      isThreeLine: true,
      trailing: new IconButton(
        icon: new Icon(Icons.add),
        onPressed: () async { Directory appDocDir = await getApplicationDocumentsDirectory();
        String appDocPath = appDocDir.path;
        new File('$appDocPath/my_file.txt').writeAsStringSync('myVar: $_currencies');  
        }
      ),
    );
  }

onPressed: () async { Directory appDocDir = await getApplicationDocumentsDirectory();

new File('$appDocPath/my_file.txt').writeAsStringSync('myVar: $_currencies');  

这是显示错误的两行：

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:cryptick/data/crypto_data.dart';
import 'package:cryptick/modules/crypto_presenter.dart';
import 'package:shimmer/shimmer.dart';
import 'dart:async';
import 'package:path_provider/path_provider.dart';

ListTile _getListItemUi(Crypto currency, MaterialColor color) {
    return new ListTile(
      leading: new Image.network("http://cryptoicons.co/32@2x/color/"+currency.symbol.toLowerCase()+"@2x.png"),
      title: new Text(currency.name,
          style: new TextStyle(fontWeight: FontWeight.bold)),
      subtitle:
      _getSubtitleText(currency.price_usd, currency.percent_change_1h),
      isThreeLine: true,
      trailing: new IconButton(
        icon: new Icon(Icons.add),
        onPressed: () async { Directory appDocDir = await getApplicationDocumentsDirectory();
        String appDocPath = appDocDir.path;
        new File('$appDocPath/my_file.txt').writeAsStringSync('myVar: $_currencies');  
        }
      ),
    );
  }

onPressed: () async { Directory appDocDir = await getApplicationDocumentsDirectory();

new File('$appDocPath/my_file.txt').writeAsStringSync('myVar: $_currencies');  

和：

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:cryptick/data/crypto_data.dart';
import 'package:cryptick/modules/crypto_presenter.dart';
import 'package:shimmer/shimmer.dart';
import 'dart:async';
import 'package:path_provider/path_provider.dart';

ListTile _getListItemUi(Crypto currency, MaterialColor color) {
    return new ListTile(
      leading: new Image.network("http://cryptoicons.co/32@2x/color/"+currency.symbol.toLowerCase()+"@2x.png"),
      title: new Text(currency.name,
          style: new TextStyle(fontWeight: FontWeight.bold)),
      subtitle:
      _getSubtitleText(currency.price_usd, currency.percent_change_1h),
      isThreeLine: true,
      trailing: new IconButton(
        icon: new Icon(Icons.add),
        onPressed: () async { Directory appDocDir = await getApplicationDocumentsDirectory();
        String appDocPath = appDocDir.path;
        new File('$appDocPath/my_file.txt').writeAsStringSync('myVar: $_currencies');  
        }
      ),
    );
  }

onPressed: () async { Directory appDocDir = await getApplicationDocumentsDirectory();

new File('$appDocPath/my_file.txt').writeAsStringSync('myVar: $_currencies');  

---

导入此文件，您就可以开始了：-

import 'dart:io';

---

导入此文件，您就可以开始了：-

import 'dart:io';

---

你的问题到底是什么？？哪个类是未定义的。那个代码示例是什么。您需要清楚地说明一些事情。“目录”和“文件”未定义，问题发生在我尝试在pubspec.yaml中为我的项目实现path_provider（需要在按下按钮时向文本文件添加字符串）后。我将此添加到我的原始问题您的问题到底是什么？？哪个类是未定义的。那个代码示例是什么。您需要清楚地说明一些事情。'Directory'和'File'未定义，问题发生在我试图在pubspec.yaml中为我的项目实现path_provider（需要在按下按钮时向文本文件添加字符串）之后。我将把这一点添加到我的原始问题谢谢您的建议，但是这并没有什么区别，因为这两个类都还没有定义：/你能告诉我哪两行显示了错误吗？检查原始问题，因为它已被编辑以反映这两行。虽然有一点值得注意，但它在“dart”和“io”之间有一个分号，而不是一个完整的句号。非常感谢你的建议，但是这并没有造成太大的区别，因为这两个类都还没有定义：/你能告诉我哪两行显示了错误吗？检查原始问题，因为它已被编辑以反映这两行。不过需要注意的是，它在“dart”和“io”之间有一个分号，而不是一个完整的stopMy bad