iOS开发中属性 property 和 synthesize

╰+攻爆jí腚メ 2022-06-06 23:59 201阅读 0赞

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        <p style="margin-top:0px; margin-bottom:0px; padding-top:0px; padding-bottom:0px; font-family:Helvetica,Tahoma,Arial,sans-serif"> <span style="margin:0px; padding:0px; color:rgb(50,62,50)">在Objective－c 2 .0中引入了 property 和 synthesize 为方便存取&nbsp;</span></p> 
        <span style="margin:0px; padding:0px">&nbsp;1 让大家认识一下 property &nbsp;and &nbsp;synthesize &nbsp;吧&nbsp;</span> 
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          @property预编译命令的作用是自动声明属性的setter和getter方法&nbsp; 
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          @synthesize也是一种新的编译器功能，表示“创建该属性的访问器” 
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          废话少说～～ 下面更精彩哦～～～ 
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          下面我们来对比一下 有这两个属性和不用这两个属性的区别吧！！！&nbsp; 
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          &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;没用之前 
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         <span style="margin:0px; padding:0px">&nbsp;// Student.h&nbsp;<br> #import &lt;Cocoa/Cocoa.h&gt;&nbsp;<br> @interface Student : NSObject { &nbsp;<br> NSString *name;&nbsp;<br> NSString *studentNO;&nbsp;<br> }&nbsp;<br> - (NSString*)name;&nbsp;<br> - (NSString*)studentNO;&nbsp;<br> - (void)setName:(NSString*)aName;&nbsp;<br> - (void)setStudentNO:(NSString*)aStudentNO;&nbsp;<br> @end&nbsp;<br> <br> </span> 
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         <span style="margin:0px; padding:0px">// Student.m&nbsp;<br> - (NSString*)name&nbsp;<br> { &nbsp;<br> return name;&nbsp;<br> }&nbsp;<br> - (NSString*)studentNO&nbsp;<br> { &nbsp;<br> return studentNO;&nbsp;<br> }&nbsp;<br> <br> - (void)setName:(NSString*)aName&nbsp;<br> { &nbsp;<br> [name autorelease];&nbsp;<br> name = [aName copy];&nbsp;<br> }&nbsp;<br> <br> - (void)setStudentNO:(NSString*)aStudentNO&nbsp;<br> { &nbsp;<br> [studentNO autorelease];&nbsp;<br> studentNO = [aStudentNO copy];&nbsp;<br> }&nbsp;<br> <br> <br> <br> </span> 
         <br> main里面这么用： &nbsp; 
         <br> Student *hayes = [[Student alloc] init]; &nbsp; 
         <br> [hayes setName:@"Hayes"]; &nbsp; 
         <br> [hayes setStudentNO:@"00000"]; &nbsp; 
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         <br> NSLog(@"Name: %@", [hayes name]); &nbsp; 
         <br> NSLog(@"Student NO: %@", [hayes studentNO]); &nbsp; 
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           用了之后&nbsp; 
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          <span style="margin:0px; padding:0px"><span style="margin:0px; padding:0px; color:rgb(138,138,138)"><span style="margin:0px; padding:0px; color:rgb(51,102,255)">// Student.h&nbsp;<br> <span style="margin:0px; padding:0px">#import &lt;Cocoa/Cocoa.h&gt;&nbsp;<br> <br> @interface Student : NSObject &lt;NSCoding&gt; { &nbsp;<br> NSString *name;&nbsp;<br> NSString *studentNO;&nbsp;<br> }&nbsp;<br> <br> @property(copy) NSString *name;&nbsp;<br> @property(copy) NSString *studentNO;&nbsp;<br> <br> @end&nbsp;<br> <br> &nbsp;</span></span></span>&nbsp;// Student.m&nbsp;<br> #import "Student.h"&nbsp;<br> <br> @implementation Student&nbsp;<br> <br> @synthesize name;&nbsp;<br> @synthesize studentNO;&nbsp;<br> <br> @end&nbsp;<br> <br> </span> 
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          <span style="margin:0px; padding:0px; color:rgb(51,102,255)">在main函数里可以这么调用：<br> <span style="margin:0px; padding:0px">Student *hayes = [[Student alloc] init];&nbsp;<br> hayes.name = @"hayes";&nbsp;<br> hayes.studentNO = @"00001";&nbsp;<br> <br> NSLog(@"%@", hayes.name);&nbsp;<br> NSLog(@"%@", hayes. studentNO);&nbsp;&nbsp;<br> <br> </span></span> 
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           <span style="margin:0px; padding:0px; color:rgb(138,138,138)"><span style="margin:0px; padding:0px; color:rgb(51,102,255)">精彩内容 马上上演～～～</span></span> 
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           <span style="margin:0px; padding:0px">2 下面请允许我非常详细的给大家介绍一下 property 后面括号中的属性（<span style="margin:0px; padding:0px; color:rgb(255,0,0)">nonatimic,retain,assign,copy,readonly,readwrite</span>,）这些属性主要事完成getter setter 的操作 &nbsp;</span> 
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           <span style="margin:0px; padding:0px">（这个很重要的哦 ！！！很多初学者都在这里迷惑哦～～～）&nbsp;</span> 
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           <span style="margin:0px; padding:0px"><span style="margin:0px; padding:0px; color:rgb(237,28,36)">assign</span>: 简单的赋值 &nbsp;不会更改<span style="margin:0px; padding:0px; color:rgb(34,177,76)">索引计数</span>（Reference &nbsp;counting）主要是对基本数据类型使用 eg：（NSInteger，CGFloat 和C语言的 int double float char &nbsp;...）如果使用对象类型的参数，需要开启garbage collector</span> 
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           <span style="margin:0px; padding:0px">［现在的版本叫引用计数器 不同的版本不同的叫法 &nbsp;在mac编程和在iphone编程中的叫法也不同 &nbsp;谅解 谅解 ］&nbsp;</span> 
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           <span style="margin:0px; padding:0px"><span style="margin:0px; padding:0px; color:rgb(255,0,0)">retain</span>: 释放旧的对象 将旧对象的值赋予输入对象 并将输入对象的索引计数＋1 ，主要应用与NSObject与其子类中，如果启用了garbage collector 和assign 的作用一样&nbsp;</span> 
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           <ol style="margin:0px 0px 1px 45px!important; padding:0px; font-size:1em; color:rgb(92,92,92)"> 
            <li style="margin:0px!important; padding:0px 3px 0px 10px!important; list-style:decimal; font-size:1em; border-width:0px 0px 0px 3px; border-style:none none none solid; border-left-color:rgb(108,226,108); color:inherit"> <span style="margin:0px; padding:0px"><span style="margin:0px; padding:0px; color:black"><span style="margin:0px; padding:0px">-&nbsp;(</span><span style="margin:0px; padding:0px; color:rgb(0,102,153)"><span style="margin:0px; padding:0px">void</span></span><span style="margin:0px; padding:0px">)setName:(NSString&nbsp;*)newName&nbsp;{&nbsp;&nbsp;</span></span></span></li> 
            <li style="margin:0px!important; padding:0px 3px 0px 10px!important; list-style:decimal; font-size:1em; border-width:0px 0px 0px 3px; border-style:none none none solid; border-left-color:rgb(108,226,108)"> <span style="margin:0px; padding:0px; color:black">&nbsp;&nbsp;&nbsp;&nbsp;<span style="margin:0px; padding:0px; color:rgb(0,102,153)"><span style="margin:0px; padding:0px">if</span></span><span style="margin:0px; padding:0px">&nbsp;(name&nbsp;!=&nbsp;newName)&nbsp;{&nbsp;&nbsp;</span></span></li> 
            <li style="margin:0px!important; padding:0px 3px 0px 10px!important; list-style:decimal; font-size:1em; border-width:0px 0px 0px 3px; border-style:none none none solid; border-left-color:rgb(108,226,108); color:inherit"> <span style="margin:0px; padding:0px; color:black">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[name&nbsp;release];&nbsp;&nbsp;</span></li> 
            <li style="margin:0px!important; padding:0px 3px 0px 10px!important; list-style:decimal; font-size:1em; border-width:0px 0px 0px 3px; border-style:none none none solid; border-left-color:rgb(108,226,108)"> <span style="margin:0px; padding:0px; color:black">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;name&nbsp;=&nbsp;[newName&nbsp;retain];&nbsp;&nbsp;</span></li> 
            <li style="margin:0px!important; padding:0px 3px 0px 10px!important; list-style:decimal; font-size:1em; border-width:0px 0px 0px 3px; border-style:none none none solid; border-left-color:rgb(108,226,108); color:inherit"> <span style="margin:0px; padding:0px; color:black">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span style="margin:0px; padding:0px; color:rgb(0,130,0)">//&nbsp;name’s&nbsp;retain&nbsp;count&nbsp;has&nbsp;been&nbsp;bumped&nbsp;up&nbsp;by&nbsp;1</span><span style="margin:0px; padding:0px">&nbsp;&nbsp;</span></span></li> 
            <li style="margin:0px!important; padding:0px 3px 0px 10px!important; list-style:decimal; font-size:1em; border-width:0px 0px 0px 3px; border-style:none none none solid; border-left-color:rgb(108,226,108)"> <span style="margin:0px; padding:0px; color:black">&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;</span></li> 
            <li style="margin:0px!important; padding:0px 3px 0px 10px!important; list-style:decimal; font-size:1em; border-width:0px 0px 0px 3px; border-style:none none none solid; border-left-color:rgb(108,226,108); color:inherit"> <span style="margin:0px; padding:0px; color:black">} &nbsp;</span></li> 
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           <span style="margin:0px; padding:0px"><span style="margin:0px; padding:0px; color:rgb(255,0,0)">copy</span>: 创建一个索引计数为1的对象 释放掉原来的对象&nbsp;</span> 
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           <span style="margin:0px; padding:0px"><span style="margin:0px; padding:0px; color:rgb(255,0,0)">readonly</span>: &nbsp;表示只读属性 &nbsp;只会生成getter方法 不会生成setter方法&nbsp;</span> 
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           <span style="margin:0px; padding:0px"><span style="margin:0px; padding:0px; color:rgb(255,0,0)">readwrite</span>:设置可供访问的级别&nbsp;</span> 
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           <span style="margin:0px; padding:0px"><span style="margin:0px; padding:0px; color:rgb(255,0,0)">nonatimic</span>:非原子访问，不加同步 ，多线程并发访问提高性能 （对多线程的保护，防止在未写完，被另一个线程读取，造成数据错误）。</span> 
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           <span style="margin:0px; padding:0px">对copy 和retain的 解释&nbsp;上面的语言太抽象了 那么请允许我在这里对 copy 和 retain 的区别 作详细的介绍</span> 
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           <p style="margin-top:1em; margin-bottom:0.5em; padding-top:0px; padding-bottom:0px"> <span style="margin:0px; padding:0px">比如一个<span style="margin:0px; padding:0px">NSString</span>&nbsp;对象，地址为<span style="margin:0px; padding:0px">0×1111</span>&nbsp;，内容为<span style="margin:0px; padding:0px">@”STR”</span></span></p> 
           <p style="margin-top:1em; margin-bottom:0.5em; padding-top:0px; padding-bottom:0px"> <span style="margin:0px; padding:0px">Copy</span>&nbsp;到另外一个NSString&nbsp;之后，地址为0×2222&nbsp;，内容相同，新的对象retain为<span style="margin:0px; padding:0px">1</span>&nbsp;，旧有对象没有变化</p> 
           <p style="margin-top:1em; margin-bottom:0.5em; padding-top:0px; padding-bottom:0px"> <span style="margin:0px; padding:0px">retain</span>&nbsp;到另外一个NSString&nbsp;之后，地址相同（建立一个指针，指针拷贝），内容当然相同，这个对象的retain值+1&nbsp;</p> 
           <p style="margin-top:1em; margin-bottom:0.5em; padding-top:0px; padding-bottom:0px"> <span style="margin:0px; padding:0px">retain</span>&nbsp;是指针拷贝，<span style="margin:0px; padding:0px">copy</span>&nbsp;是内容拷贝 &nbsp;</p> 
           <p style="margin-top:1em; margin-bottom:0.5em; padding-top:0px; padding-bottom:0px"> 下面分享一个网友的总结</p> 
           <p style="margin-top:1em; margin-bottom:0.5em; padding-top:0px; padding-bottom:0px"> &nbsp;</p> 
           <p style="margin-top:0px; margin-bottom:1em; padding-top:0px; padding-bottom:0px"> <span style="margin:0px; padding:0px; font-size:13px; color:rgb(111,94,78)">一直以来个人觉得如果一个类是的property是readonly的那么再指定其他的如assign/retain/copy这样的属性就实在是没有什么意义了。确实你想想既然都readonly了，肯定是没有setter的，既然没有setter那么谈assign/retain/copy又有什么意义呢？所以一直以来我从来不对readonly的property加retain/copy属性申明，默认assign就足够了，simple is beautiful！</span></p> 
           <p style="margin-top:0px; margin-bottom:1em; padding-top:0px; padding-bottom:0px"> 但是我现在发现我错了，其实一直都有一种这种感觉，只是没有找到100％的充分理由为readonly加上retain/copy。但是假如你要在你的subclass改写property，而加入你要改写的是一个NSString，你像把这个属性设置为readwrite和copy，往往杯具就发生了，编译时候可恶的warning 产生了，因为copy和之前默认的assign明显不相同啊！</p> 
           <p style="margin-top:0px; margin-bottom:1em; padding-top:0px; padding-bottom:0px"> 终上，不论什么时候，<span style="margin:0px; padding:0px">都要为你的readonly的对象属性加上合适的retain/copy申明</span>。你现在不用，但不说明你将来就不会用，出来混迟早都要还的！</p> 
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