代码拉取完成，页面将自动刷新
<!DOCTYPE HTML>
<html lang="" >
<head>
<meta charset="UTF-8">
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<title>消息传递的方式 · GitBook</title>
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="description" content="">
<meta name="generator" content="GitBook 3.2.3">
<link rel="stylesheet" href="gitbook/style.css">
<link rel="stylesheet" href="gitbook/gitbook-plugin-highlight/website.css">
<link rel="stylesheet" href="gitbook/gitbook-plugin-search/search.css">
<link rel="stylesheet" href="gitbook/gitbook-plugin-fontsettings/website.css">
<meta name="HandheldFriendly" content="true"/>
<meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no">
<meta name="apple-mobile-web-app-capable" content="yes">
<meta name="apple-mobile-web-app-status-bar-style" content="black">
<link rel="apple-touch-icon-precomposed" sizes="152x152" href="gitbook/images/apple-touch-icon-precomposed-152.png">
<link rel="shortcut icon" href="gitbook/images/favicon.ico" type="image/x-icon">
<link rel="next" href="Network.html" />
<link rel="prev" href="Memory-management.html" />
</head>
<body>
<div class="book">
<div class="book-summary">
<div id="book-search-input" role="search">
<input type="text" placeholder="Type to search" />
</div>
<nav role="navigation">
<ul class="summary">
<li class="chapter " data-level="1.1" data-path="./">
<a href="./">
关于
</a>
</li>
<li class="header">Part I</li>
<li class="chapter " data-level="2.1" data-path="Data-structure.html">
<a href="Data-structure.html">
数据结构
</a>
</li>
<li class="chapter " data-level="2.2" data-path="Arithmetic.html">
<a href="Arithmetic.html">
算法
</a>
</li>
<li class="header">Part II</li>
<li class="chapter " data-level="3.1" data-path="Foundation.html">
<a href="Foundation.html">
Foundation
</a>
</li>
<li class="chapter " data-level="3.2" data-path="UIKit.html">
<a href="UIKit.html">
UIKit
</a>
</li>
<li class="chapter " data-level="3.3" data-path="WebView.html">
<a href="WebView.html">
WebView
</a>
</li>
<li class="chapter " data-level="3.4" data-path="Memory-management.html">
<a href="Memory-management.html">
内存管理
</a>
</li>
<li class="chapter active" data-level="3.5" data-path="Message-passing.html">
<a href="Message-passing.html">
消息传递的方式
</a>
</li>
<li class="chapter " data-level="3.6" data-path="Network.html">
<a href="Network.html">
网络
</a>
</li>
<li class="chapter " data-level="3.7" data-path="Data-storage.html">
<a href="Data-storage.html">
数据存储
</a>
</li>
<li class="chapter " data-level="3.8" data-path="Multi-thread.html">
<a href="Multi-thread.html">
多线程
</a>
</li>
<li class="chapter " data-level="3.9" data-path="Animation.html">
<a href="Animation.html">
动画
</a>
</li>
<li class="chapter " data-level="3.10" data-path="Image-processing.html">
<a href="Image-processing.html">
图像处理
</a>
</li>
<li class="chapter " data-level="3.11" data-path="Data-encryption.html">
<a href="Data-encryption.html">
数据安全及加密
</a>
</li>
<li class="chapter " data-level="3.12" data-path="Runtime.html">
<a href="Runtime.html">
Runtime
</a>
</li>
<li class="chapter " data-level="3.13" data-path="Runloop.html">
<a href="Runloop.html">
Runloop
</a>
</li>
<li class="header">Part III</li>
<li class="chapter " data-level="4.1" data-path="Project-organization.html">
<a href="Project-organization.html">
项目架构
</a>
</li>
<li class="chapter " data-level="4.2" data-path="Design-patterns.html">
<a href="Design-patterns.html">
设计模式
</a>
</li>
<li class="chapter " data-level="4.3" data-path="Component-based.html">
<a href="Component-based.html">
组件化
</a>
</li>
<li class="chapter " data-level="4.4" data-path="Debug-tips.html">
<a href="Debug-tips.html">
调试技巧
</a>
</li>
<li class="chapter " data-level="4.5" data-path="Performance-optimization.html">
<a href="Performance-optimization.html">
性能优化
</a>
</li>
<li class="chapter " data-level="4.6" data-path="Source-code.html">
<a href="Source-code.html">
源码理解
</a>
</li>
<li class="chapter " data-level="4.7" data-path="Code-management.html">
<a href="Code-management.html">
代码管理
</a>
</li>
<li class="chapter " data-level="4.8" data-path="Continuous-integration.html">
<a href="Continuous-integration.html">
持续集成
</a>
</li>
<li class="divider"></li>
<li>
<a href="https://www.gitbook.com" target="blank" class="gitbook-link">
Published with GitBook
</a>
</li>
</ul>
</nav>
</div>
<div class="book-body">
<div class="body-inner">
<div class="book-header" role="navigation">
<!-- Title -->
<h1>
<i class="fa fa-circle-o-notch fa-spin"></i>
<a href="." >消息传递的方式</a>
</h1>
</div>
<div class="page-wrapper" tabindex="-1" role="main">
<div class="page-inner">
<div id="book-search-results">
<div class="search-noresults">
<section class="normal markdown-section">
<h1 id="消息传递的方式">消息传递的方式</h1>
<h2 id="1kvc实现原理">1.KVC实现原理</h2>
<ul>
<li><p>KVC，键-值编码，使用字符串直接访问对象的属性。</p>
</li>
<li><p>底层实现，当一个对象调用setValue方法时，方法内部会做以下操作：</p>
<p> 1.检查是否存在相应key的set方法，如果存在，就调用set方法</p>
<p> 2.如果set方法不存在，就会查找与key相同名称并且带下划线的成员属性，如果有，则直接给成员属性赋值</p>
<p> 3.如果没有找到_key，就会查找相同名称的属性key，如果有就直接赋值</p>
<p> 4.如果还没找到，则调用valueForUndefinedKey：和setValue：forUndefinedKey：方法</p>
</li>
</ul>
<h2 id="2kvo的实现原理">2.KVO的实现原理</h2>
<p><img src="https://qn.nobady.cn/iOS/kvo.png" alt="KVO"></p>
<p>KVO-键值观察机制，原理如下：</p>
<ul>
<li><p>1.当给A类添加KVO的时候，runtime动态的生成了一个子类NSKVONotifying_A，让A类的isa指针指向NSKVONotifying_A类，重写class方法，隐藏对象真实类信息</p>
</li>
<li><p>2.重写监听属性的setter方法，在setter方法内部调用了Foundation 的 _NSSetObjectValueAndNotify 函数</p>
</li>
<li><p>3._NSSetObjectValueAndNotify函数内部</p>
<p> a) 首先会调用 willChangeValueForKey </p>
<p> b) 然后给属性赋值 </p>
<p> c) 最后调用 didChangeValueForKey </p>
<p> d) 最后调用 observer 的 observeValueForKeyPath 去告诉监听器属性值发生了改变 .</p>
</li>
<li><p>4.重写了dealloc做一些 KVO 内存释放 </p>
</li>
</ul>
<h2 id="3如何手动触发kvo方法">3.如何手动触发KVO方法</h2>
<ul>
<li><p>手动调用willChangeValueForKey和didChangeValueForKey方法</p>
</li>
<li><p>键值观察通知依赖于 NSObject 的两个方法: willChangeValueForKey: 和 didChangeValueForKey。在一个被观察属性发生改变之前， willChangeValueForKey: 一定会被调用，这就 会记录旧的值。而当改变发生后， didChangeValueForKey 会被调用，继而 observeValueForKey:ofObject:change:context: 也会被调用。如果可以手动实现这些调用，就可以实现“手动触发”了
有人可能会问只调用didChangeValueForKey方法可以触发KVO方法，其实是不能的，因为willChangeValueForKey: 记录旧的值，如果不记录旧的值，那就没有改变一说了</p>
</li>
</ul>
<h2 id="4通知和代理有什么区别">4.通知和代理有什么区别</h2>
<ul>
<li><p>通知是观察者模式，适合一对多的场景</p>
</li>
<li><p>代理模式适合一对一的反向传值</p>
</li>
<li><p>通知耦合度低，代理的耦合度高</p>
</li>
</ul>
<h2 id="5block和delegate的区别">5.block和delegate的区别</h2>
<ul>
<li><p>delegate运行成本低，block的运行成本高</p>
<p> block出栈需要将使用的数据从栈内存拷贝到堆内存，当然对象的话就是加计数，使用完或者block置nil后才消除。delegate只是保存了一个对象指针，直接回调，没有额外消耗。就像C的函数指针，只多做了一个查表动作。</p>
</li>
<li><p>delegate更适用于多个回调方法（3个以上），block则适用于1，2个回调时。</p>
</li>
</ul>
<h2 id="6为什么block用copy关键字">6.为什么Block用copy关键字</h2>
<p>Block在没有使用外部变量时，内存存在全局区，然而，当Block在使用外部变量的时候，内存是存在于栈区，当Block copy之后，是存在堆区的。存在于栈区的特点是对象随时有可能被销毁，一旦销毁在调用的时候，就会造成系统的崩溃。所以Block要用copy关键字。</p>
</section>
</div>
<div class="search-results">
<div class="has-results">
<h1 class="search-results-title"><span class='search-results-count'></span> results matching "<span class='search-query'></span>"</h1>
<ul class="search-results-list"></ul>
</div>
<div class="no-results">
<h1 class="search-results-title">No results matching "<span class='search-query'></span>"</h1>
</div>
</div>
</div>
</div>
</div>
</div>
<a href="Memory-management.html" class="navigation navigation-prev " aria-label="Previous page: 内存管理">
<i class="fa fa-angle-left"></i>
</a>
<a href="Network.html" class="navigation navigation-next " aria-label="Next page: 网络">
<i class="fa fa-angle-right"></i>
</a>
</div>
<script>
var gitbook = gitbook || [];
gitbook.push(function() {
gitbook.page.hasChanged({"page":{"title":"消息传递的方式","level":"3.5","depth":1,"next":{"title":"网络","level":"3.6","depth":1,"path":"Network.md","ref":"Network.md","articles":[]},"previous":{"title":"内存管理","level":"3.4","depth":1,"path":"Memory-management.md","ref":"Memory-management.md","articles":[]},"dir":"ltr"},"config":{"gitbook":"*","theme":"default","variables":{},"plugins":["livereload"],"pluginsConfig":{"livereload":{},"highlight":{},"search":{},"lunr":{"maxIndexSize":1000000,"ignoreSpecialCharacters":false},"sharing":{"facebook":true,"twitter":true,"google":false,"weibo":false,"instapaper":false,"vk":false,"all":["facebook","google","twitter","weibo","instapaper"]},"fontsettings":{"theme":"white","family":"sans","size":2},"theme-default":{"styles":{"website":"styles/website.css","pdf":"styles/pdf.css","epub":"styles/epub.css","mobi":"styles/mobi.css","ebook":"styles/ebook.css","print":"styles/print.css"},"showLevel":false}},"structure":{"langs":"LANGS.md","readme":"README.md","glossary":"GLOSSARY.md","summary":"SUMMARY.md"},"pdf":{"pageNumbers":true,"fontSize":12,"fontFamily":"Arial","paperSize":"a4","chapterMark":"pagebreak","pageBreaksBefore":"/","margin":{"right":62,"left":62,"top":56,"bottom":56}},"styles":{"website":"styles/website.css","pdf":"styles/pdf.css","epub":"styles/epub.css","mobi":"styles/mobi.css","ebook":"styles/ebook.css","print":"styles/print.css"}},"file":{"path":"Message-passing.md","mtime":"2020-04-13T10:23:32.000Z","type":"markdown"},"gitbook":{"version":"3.2.3","time":"2020-05-27T09:12:21.691Z"},"basePath":".","book":{"language":""}});
});
</script>
</div>
<script src="gitbook/gitbook.js"></script>
<script src="gitbook/theme.js"></script>
<script src="gitbook/gitbook-plugin-livereload/plugin.js"></script>
<script src="gitbook/gitbook-plugin-search/search-engine.js"></script>
<script src="gitbook/gitbook-plugin-search/search.js"></script>
<script src="gitbook/gitbook-plugin-lunr/lunr.min.js"></script>
<script src="gitbook/gitbook-plugin-lunr/search-lunr.js"></script>
<script src="gitbook/gitbook-plugin-sharing/buttons.js"></script>
<script src="gitbook/gitbook-plugin-fontsettings/fontsettings.js"></script>
</body>
</html>
此处可能存在不合适展示的内容，页面不予展示。您可通过相关编辑功能自查并修改。
如您确认内容无涉及 不当用语 / 纯广告导流 / 暴力 / 低俗色情 / 侵权 / 盗版 / 虚假 / 无价值内容或违法国家有关法律法规的内容，可点击提交进行申诉，我们将尽快为您处理。