July 2020
Intermediate to advanced
235 pages
3h 37m
Chinese
Content preview from Kotlin 编程实践
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131
第
8
章
Kotlin 委托
本章将讨论 Kotlin 中的委托。你将学习到如何使用标准库中的委托，包括lazy、
observable、vetoable 以及 notNull，并创建自己的委托。
类委托
可以让你使用
组合代替继承，而
属性委托
则可以使用来自另一个类的属性来替换当前属性的 getter 与
setter。
除了基本的演示之外，本章也展示了标准的委托是如何在库中实现的，以作为良好使用
习惯的用例。
8.1
使用委托实现组合
问题
如何创建一个类，该类包含另一个类的实例，并将行为委托给它们。
解决方案
创建包含委托方法的接口，并在类中实现这些接口，然后使用关键字 by 来用它们构建
包装器类。
讨论
现代的面向对象设计趋向于使用组合而不是继承
注 1
来作为增加功能而不需要强耦合的方
式。在 Kotlin 中，关键字 by 允许一个类通过容器公开所有包含的对象中的公有函数。
注 1： 一个真正的坏笑话：贝多芬的父母不给他继承遗产，除非他放弃音乐创作，但他仍然选择作曲而
不是继承（画外音：此外，老实说，这不是真的）。
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例如，smartphone（智能手机）同时包含电话（phone）与相机（camera），以及大量的其
他组件。如果你将智能手机看作一个
包装器
对象，将内部的电话与相机看作
包含
对象， ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.