# 库 lib

本文作者：阳九五 (opens new window)

本站地址：https://blog.56321654.xyz (opens new window)

# 导入核心库

import 'dart:io';

void main() {
  var f = new File('README.md');
  var content = f.readAsStringSync();
  print(content);
}

# Dart 语言学习示例

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# 导入第三方库

编写根目录下面的pubspec.yaml文件

dependencies:
  dio: ^4.0.6

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执行拉取包命令

$ dart pub get

3.程序套用

import 'package:dio/dio.dart';

void main() async {
  Dio dio = Dio();
  Response<String> response =
      await dio.get("https://wpapi.ducafecat.tech/products/categories");
  print(response.data);
}

[{"id":34,"name":"Bag","slug":"bag","parent":0,"description":" ......

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# 导入自己的 git 仓库

编写根目录下面的pubspec.yaml文件

dependencies:
  uuid:
    git:
      url: https://github.com/Daegalus/dart-uuid
      ref: master

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执行拉取包命令

$ dart pub get

从 master 分支拉取

# 导入类文件

phone.dart

class Phone {
  void call() {
    print('Phone is calling...');
  }
}

class Android {
  void playStore() {
    print('Google play store');
  }

  void call() {
    print('Android phone is calling...');
  }
}

class Ios {
  void appleStore() {
    print('Apply store');
  }

  void call() {
    print('Ios phone is calling...');
  }
}

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hello.dart

class Hello {
    void call() {
        print('Hello Dart');
    }
}

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dev_pubspec 是 dev_pubspec.yaml 里面的name字段

import 'package:dev_pubspec/phone.dart';  // phone.dart的路径是在lib文件夹里面
import 'hello.dart';  // hello.dart的路径是相对当前文件

void main() {
    var p = Phone();
    p.call();

    var h = Hello();
    h.call();
}

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# 前缀&别名

as 关键字可以为package增加一个前缀&别名

import 'package:dart_learn/phone.dart' as pp;

void main() {
  var p = pp.Android();
  p.call();
  p.playStore();
}

Android phone is calling...
Google play store

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# 筛选包内容

import 'package:dart_learn/phone.dart' show Ios;

void main() {
  var p = Ios();
  p.call();
  p.appleStore();
}

Ios phone is calling...
Apply store

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hide 筛掉某几个包 show 只使用某几个包

# 延迟载入

deferred 关键字表明这个 package 是延迟加载

import 'package:dart_learn/phone.dart' deferred as pp;

Future<void> main() async {
  await pp.loadLibrary();
  var p = pp.Android();
  p.call();
  p.playStore();
}

Android phone is calling...
Google play store

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loadLibrary() 方式在需要的时候载入包可提高程序启动速度用在不常使用的功能用在载入时间过长的包

← 工厂函数 factory 泛型 generices →