<p>Objective-C中，类的实例化变量的范围有@private、@protected、@public。他们代表的意思和C++中相同，只是前面添加了一个@符号。下面介绍一下他们代表的范围：</p>    <table class="ke-zeroborder" border="0" cellspacing="0" cellpadding="2">     <tbody>      <tr>       <td>指令</td>       <td>意思</td>      </tr>      <tr>       <td> <p>@private</p> </td>       <td>作用范围只能在自身类</td>      </tr>      <tr>       <td>@protected</td>       <td>作用范围在自身类和继承自己的子类，什么都不写，默认是此属性。</td>      </tr>      <tr>       <td>@public</td>       <td>作用范围最大，在任何地方</td>      </tr>     </tbody>    </table>    <p>下面是官方的图：</p>    <p><a href="/misc/goto?guid=4959500540007304927" rel="nofollow"><img title="image" alt="Objective-C 中public、protected、private 的使用" src="https://simg.open-open.com/show/1b513b1d317d48127087eb44b084f2a8.png" width="284" height="242" /></a></p>    <p>具体的可以参考：<a href="/misc/goto?guid=4959500540096662858" rel="nofollow">http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocDefiningClasses.html#//apple_ref/doc/uid/TP30001163-CH12-SW1</a></p>    <p></p>    <p>下面是一个例子，来说明他们之间的关系：</p>    <p>实现一个Boss类：</p>    <pre class="brush:cpp; toolbar: true; auto-links: false;">    #import                     <foundation foundation.h="">                               <span class="referer">@interface</span> Boss : NSObject     {                              <span class="referer">@private</span>         int age;     @protected         NSString *job;     }     @end                    </foundation></pre>实现一个Worker类继承Boss类：    <pre class="brush:cpp; toolbar: true; auto-links: false;">#import                     <foundation foundation.h="">                          #import "Boss.h"                         <span class="referer">@interface</span> Worker : Boss {     NSString *name;                         <span class="referer">@private</span>     NSString *evaluation; @protected     float wage;                         <span class="referer">@public</span>     NSString *boss; } - promoteTo:newPosition; @end                    </foundation></pre>在Worker的.m文件中添加：    <pre class="brush:cpp; toolbar: true; auto-links: false;">    #import "Worker.h"      @implementation Worker     - promoteTo:newPosition     {         id old = job;         job = newPosition;         return old;     }     -(NSString *)description     {         return [NSString stringWithFormat:@"Worker name:%@,evaluation:%@,job:%@,wage:%f,boss:%@",name,evaluation,job,wage,boss];     }     @end</pre>    <p>如果我们在Worker中调用Boss中的私有变量age，会报错：</p>    <p><img title="image" alt="Objective-C 中public、protected、private 的使用" src="https://simg.open-open.com/show/f3a1a896912009f13769be6a6608fa5c.png" width="391" height="65" /></p>    <p>但是调用job是没有问题的。</p>    <p>下面在其他类中调用Worker类：</p>    <pre class="brush:cpp; toolbar: true; auto-links: false;">Worker *ceo = [[Worker alloc] init];    ceo->boss = @"XX";    [ceo promoteTo:@"YY"];     NSLog(@">>>=%@",[ceo description]); </pre>    <p>运行结果：</p>    <p><img title="image" alt="Objective-C 中public、protected、private 的使用" src="https://simg.open-open.com/show/abcdf7dce6737cb4f3cb2f28cb52ea0f.png" width="422" height="27" /></p>    <p>但是调用protected的属性会报错：</p>    <p><img title="image" alt="Objective-C 中public、protected、private 的使用" src="https://simg.open-open.com/show/0e3fd8a00c285e82014b3955d1bf22b0.png" width="413" height="25" /></p>    <p>所以当一些比较重要的属性，不能随便更改的时候，要用private，这样避免其他继承类修改此属性。</p>    <p>文章出处：<a href="/misc/goto?guid=4959500540176191654" rel="nofollow">http://wangjun.easymorse.com/?p=1615</a></p>