Flutter 零件和导出-dart的用途是什么？

我是飞镖和飞镖的初学者。我在GitHub上看到了很多使用part和export关键字的示例。我在谷歌上搜索过，但还是不太清楚。我已经看过答案了

不过，我还是不明白。也许有点长，我不是以英语为母语的人

为什么这些关键词会被使用

他们做什么

---

下面是一个由3个文件组成的简单代码示例。两个文件组成库，一个使用库。所有功能的说明都包含在整个文件的注释中

图书馆

// declare a name for this library to reference from parts
// this is not necessary if we do not need to reference elsewhere
// NOTE: generally, a Dart file is a Library
library counter;

// export adds contents of another Library to this Library's namespace
// here we are adding all content (accessible from outside the library) from
// the material library
// NOTE: this is intended for related libraries
// this arbitrary usage is simply for demonstration purposes
export 'package:flutter/material.dart';

// for finer control, we can use the 'show' directive
// try this to see the effects of selected export
// export 'package:flutter/material.dart' show StatefulWidget, State;

// include any files containing parts of this library
part 'library_part.dart';

class Counter extends AbstractCounter {
  // we can access library private variable _count even though it is in a different
  // file because we made it part of the same library
  reset() => _count = 0;
}

库_零件.dart

// declare this file as part of the counter library
part of counter;

abstract class AbstractCounter {
  // this is a library private variable (_varName)
  // if this file were not made part of the counter library, this variable
  // would not be accessible to the Counter class in library_main.dart
  // this is an important concept to understand about Dart's library privacy
  // it differs from class based privacy, like that used in Java
  int _count = 0;

  get count => _count;
  increment() => ++_count;
}

library\u示例.dart

// note that 'material.dart' does not need to be imported
// because it has been exported with the counter library
import 'library_main.dart';

class LibraryExample extends StatefulWidget {
  @override
  _LibraryExampleState createState() => _LibraryExampleState();
}

class _LibraryExampleState extends State<LibraryExample> {
  final _counter = Counter();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Library Example'),
      ),
      body: Center(
        child: Text('You have pressed the button ${_counter.count} times.'),
      ),
      floatingActionButton: Row(
        mainAxisAlignment: MainAxisAlignment.end,
        children: [
          FloatingActionButton(
            child: Text('Reset'),
            onPressed: () => setState(() => _counter.reset()),
          ),
          SizedBox(width: 10),
          FloatingActionButton(
            child: Icon(Icons.add),
            onPressed: () => setState(() => _counter.increment()),
          ),
        ],
      ),
    );
  }
}

//请注意，不需要导入“material.dart”
//因为它已与计数器库一起导出
导入“library_main.dart”；
类库示例扩展StatefulWidget{
@凌驾
_LibraryExampleState createState（）=>\u LibraryExampleState（）；
}
类_LibraryExampleState扩展状态{
最终计数器=计数器（）；
@凌驾
小部件构建（构建上下文）{
返回脚手架(
appBar:appBar(
标题：文本（“库示例”），
),
正文：中(
child:Text（'您已按下按钮${u counter.count}次。'），
),
浮动操作按钮：行(
mainAxisAlignment:mainAxisAlignment.end，
儿童：[
浮动操作按钮(
子项：文本（“重置”），
按下时：（）=>设置状态（（）=>_counter.reset（）），
),
尺寸箱（宽度：10），
浮动操作按钮(
子：图标（Icons.add），
按下时：（）=>设置状态（（）=>_counter.increment（）），
),
],
),
);
}
}

这是否回答了您的问题？我不是以英语为母语的人。所以simple engish只帮助meSo你是说一个简单的dart文件可以称为库，导出就会导入库。那个么第二部分呢？我已经更新了我的答案，以便更好地解决每个关键词。你们能举一个简单的导出示例吗。那真的很有帮助没问题。查看更新的答案。我已经包括了一个简单的实现和大量的评论。希望能有帮助。