Flutter Packages 开发（一）

Package 介绍

通过使用 packages （的模式）可以创建易于共享的模块化代码。一个最基本的 package 由以下内容构成：

• pubspec.yaml 文件
  用于定义 package 名称、版本号、作者等其他信息的元数据文件。
• lib 目录
  包含共享代码的 lib 目录，其中至少包含一个 .dart 文件。

Package 类别

纯 Dart 库 (Dart packages)

用 Dart 编写的传统 package，比如 上面的gift_board_component UI组件包，纯dart的工具类包。其中一些可能包含 Flutter 的特定功能，因此依赖于 Flutter 框架，其使用范围仅限于 Flutter，没有调用原生功能代码的需求。

原生插件 (Plugin packages)

使用 Dart 编写的，按需使用 Java 或 Kotlin、ObjC 或 Swift 分别在 Android 和/或 iOS 平台实现的 package。有调用原生功能代码的需求

开发纯 Dart 库的 packages

第一步：创建 package

flutter create --template=package hello_plugin

其中 hello_plugin为包的名称

会在hello_plugin目录生成以下文件：

image.png

其中就有最基础的两个文件：pubspec.yaml 和 lib文件夹
将默认生成的hello_plugin.dart文件修改一下

library hello_plugin;

abstract class HelloPluginInterface{
  int addOne(int value);
}

class HelloPlugin extends HelloPluginInterface {

  @override
  int addOne(int value) {
    return value + 1;
  }

}

第二步：实现 package

对于纯 Dart 库的 package，只要在 lib/.dart 文件中添加功能实现，或在 lib 目录中的多个文件中添加功能实现。
如果要对 package 进行测试，在 test 目录下添加 单元测试。
关于如何组织 package 内容的更多详细信息，请参考 Dart library package 文档

常见的目录结构如下：

image.png

说明：

• example ：使用例子
• lib : src(源码目录) + .dart 或者其他需要单独公开的功能（如shelf_io.dart）
• test: 单元测试目录
• tool: 工具目录，如一些批处理工具文件

由于纯dart库（不依赖Flutter的视图框架），基本没有其他步骤了。
下面主要说明一下实现UI组件package

1. 实现UI组件package

1.1 生成example工程

在上面的hello_plugin目录下执行

flutter create -i objc -a kotlin example

命令说明:-i 指定ios开发语言； -a指定android开发语言；

会在hello_plugin目录下生成example目录；example中包含android, ios 原生工程目录：

下面以android开发为例：
使用android studio 打开hello_plugin项目

1.2 在example中依赖本地库hello_plugin

在example目录中的pubspec.yaml文件中加入

hello_plugin:
  path: ../

其中：

• hello_plugin：包的名称
• path为本地hello_plugin库lib目录所在的目录

1.3 使用pub get来获取依赖库

使用android studio中的

image.png

1.4 使用本地库开发

exmple目录下的lib目录：main.dart

导入hello_plugin.dart

import 'package:hello_plugin/hello_plugin.dart';

在_MyHomePageState中声明HelloPlugin

HelloPlugin helloPlugin = HelloPlugin();

点击按钮执行_incrementCounter()方法将_counter的值进行自增

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 = helloPlugin.addOne(_counter);
    });
  }

import 'package:flutter/material.dart';
import 'package:hello_plugin/hello_plugin.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // 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: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required 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
  State createState() => _MyHomePageState();
}

class _MyHomePageState extends State {
  int _counter = 0;
  HelloPlugin helloPlugin = HelloPlugin();

  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 = helloPlugin.addOne(_counter);
    });
  }

  @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: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

参考

Flutter Packages 的开发和提交