WeakSelf iOS开发小技巧之--WeakSelf宏的进化

本文介绍了一种在Objective-C中使用宏定义简化弱引用的方法,通过逐步进化宏定义,提高了代码的可读性和便捷性。


我们都知道在防止如block的循环引用时,会使用__weak关键字做如下定义:

<code class="hljs objectivec has-numbering" style="background: none; padding: 0px; border-radius: 0px; color: inherit; font-family: 'Source Code Pro', monospace;font-size:undefined; display: block; white-space: pre; -ms-word-wrap: normal; box-sizing: border-box;">__<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">weak</span> typeof(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>) weakSelf = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>;</code><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul>

后来,为了方便,不用每次都要写这样一句固定代码,我们定义了宏:

<code class="hljs smalltalk has-numbering" style="background: none; padding: 0px; border-radius: 0px; color: inherit; font-family: 'Source Code Pro', monospace;font-size:undefined; display: block; white-space: pre; -ms-word-wrap: normal; box-sizing: border-box;"><span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">#define</span> <span class="hljs-class" style="color: rgb(102, 0, 102); box-sizing: border-box;">WeakSelf</span> __weak typeof(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>) weakSelf = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>;</code><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul>

之后,我们可以比较方便的在需要的地方:

<code class="hljs r has-numbering" style="background: none; padding: 0px; border-radius: 0px; color: inherit; font-family: 'Source Code Pro', monospace;font-size:undefined; display: block; white-space: pre; -ms-word-wrap: normal; box-sizing: border-box;">WeakSelf;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
[weakSelf doSomething];</code><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li><li style="padding: 0px 5px; box-sizing: border-box;">2</li><li style="padding: 0px 5px; box-sizing: border-box;">3</li></ul><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li><li style="padding: 0px 5px; box-sizing: border-box;">2</li><li style="padding: 0px 5px; box-sizing: border-box;">3</li></ul>

再后来,我们发现不止self需要使用weak,可能有部分变量也需要weak,于是我们的宏继续进化,不仅仅只支持self:

<code class="hljs cs has-numbering" style="background: none; padding: 0px; border-radius: 0px; color: inherit; font-family: 'Source Code Pro', monospace;font-size:undefined; display: block; white-space: pre; -ms-word-wrap: normal; box-sizing: border-box;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="color: rgb(68, 68, 68); box-sizing: border-box;">define</span> WeakObj(o) __weak typeof(o) o##Weak = o;</span></code><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul>

这样,后续对需要使用weak的对象,只要写一句WeakObj(obj) 即可使用objWeak变量了(PS:发现没有,这里生成的变量名其实是objWeak,并不是weakObj,原因见文章末的注1)

再后来,我们发现了一些小技巧,可以让我们的这个宏看起来更原生一些,我们添加了@符号在前面:

<code class="hljs cs has-numbering" style="background: none; padding: 0px; border-radius: 0px; color: inherit; font-family: 'Source Code Pro', monospace;font-size:undefined; display: block; white-space: pre; -ms-word-wrap: normal; box-sizing: border-box;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="color: rgb(68, 68, 68); box-sizing: border-box;">define</span> WeakObj(o) autoreleasepool{} __weak typeof(o) o##Weak = o;</span></code><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul>

使用上看起来是这样

<code class="hljs r has-numbering" style="background: none; padding: 0px; border-radius: 0px; color: inherit; font-family: 'Source Code Pro', monospace;font-size:undefined; display: block; white-space: pre; -ms-word-wrap: normal; box-sizing: border-box;">@WeakObj(self);
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">...</span>
[selfWeak doSomething];</code><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li><li style="padding: 0px 5px; box-sizing: border-box;">2</li><li style="padding: 0px 5px; box-sizing: border-box;">3</li></ul><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li><li style="padding: 0px 5px; box-sizing: border-box;">2</li><li style="padding: 0px 5px; box-sizing: border-box;">3</li></ul>

是不是感觉挺高大上的? 
这里是利用了@autoreleasepool{}这个系统的关键字来实现的,其实还可以利用@try{}@finally{}这个也可以达到相同的效果,比如:

<code class="hljs css has-numbering" style="background: none; padding: 0px; border-radius: 0px; color: inherit; font-family: 'Source Code Pro', monospace;font-size:undefined; display: block; white-space: pre; -ms-word-wrap: normal; box-sizing: border-box;"><span class="hljs-id" style="color: rgb(155, 112, 63); box-sizing: border-box;">#define</span> <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">WeakObj</span>(<span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">o</span>) <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">try</span><span class="hljs-rules" style="box-sizing: border-box;">{<span class="hljs-rule" style="box-sizing: border-box;">}</span></span><span class="hljs-at_rule" style="box-sizing: border-box;">@<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">finally{}</span> __weak <span class="hljs-function" style="color: rgb(0, 102, 102); box-sizing: border-box;">typeof(o)</span> o##Weak = o</span>;</code><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul>

这部分空的@try或者空的@autoreleasepool会在编译时被优化掉,不必担心性能问题。


至此,我们的宏已经可以用了,但是实际使用中,出现了一个很尴尬的问题,就是代码自动补全,@W并不能自动提示出该宏,所以每次都是很尴尬的先利用提示,写完WeakObj(obj),然后光标移动到前面去打上一个@符号。 
这种事情怎么能忍受? 
还好我们还有利器,Xcode的CodeSnippet,任意方法内,写一句代码

<code class="hljs ruby has-numbering" style="background: none; padding: 0px; border-radius: 0px; color: inherit; font-family: 'Source Code Pro', monospace;font-size:undefined; display: block; white-space: pre; -ms-word-wrap: normal; box-sizing: border-box;"><span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@WeakObj</span>(<<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">#obj#>);</span></code><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul>

拖到Xcode的CodeSnippet区域,快捷键设置为@WeakObj即可。 
这里写图片描述

至此,愉快的使用@W即可自动补全出该宏了。。


另外,还有相应的strong宏,一并晒在这里

<code class="hljs cs has-numbering" style="background: none; padding: 0px; border-radius: 0px; color: inherit; font-family: 'Source Code Pro', monospace;font-size:undefined; display: block; white-space: pre; -ms-word-wrap: normal; box-sizing: border-box;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="color: rgb(68, 68, 68); box-sizing: border-box;">define</span> StrongObj(o) autoreleasepool{} __strong typeof(o) o = o##Weak;</span></code><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li></ul>

用处嘛简单写个例子:

<code class="hljs ruby has-numbering" style="background: none; padding: 0px; border-radius: 0px; color: inherit; font-family: 'Source Code Pro', monospace;font-size:undefined; display: block; white-space: pre; -ms-word-wrap: normal; box-sizing: border-box;"><span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@WeakObj</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>);
[var <span class="hljs-symbol" style="color: rgb(0, 102, 102); box-sizing: border-box;">setBlock:</span>^{
    <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@StrongObj</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>);
    [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> doSomething];
}];</code><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li><li style="padding: 0px 5px; box-sizing: border-box;">2</li><li style="padding: 0px 5px; box-sizing: border-box;">3</li><li style="padding: 0px 5px; box-sizing: border-box;">4</li><li style="padding: 0px 5px; box-sizing: border-box;">5</li></ul><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li><li style="padding: 0px 5px; box-sizing: border-box;">2</li><li style="padding: 0px 5px; box-sizing: border-box;">3</li><li style="padding: 0px 5px; box-sizing: border-box;">4</li><li style="padding: 0px 5px; box-sizing: border-box;">5</li></ul>

关于这么写的原因,请先自行揣摩,之后可以看看晓月的这篇文章:http://blog.youkuaiyun.com/uxyheaven/article/details/44226395,也可以在评论中留言。



最后,揭晓为什么该宏生成的变量名是objWeak: 
1. 使用时,如果开发者习惯性的要打出 [self doSomething]时,当他输入self时,自动补全出来的部分能看到还有selfWeak可供选择,算是一种提醒方式。 
2. 如果weak前置,当然也可以,生成的会是weakobj这样的变量名,只需要把宏中o##Weak 换成weak##o

好了,这篇文章希望对一些人有些启发或帮助。

最后晒出个人在用的宏定义:

<code class="hljs cs has-numbering" style="background: none; padding: 0px; border-radius: 0px; color: inherit; font-family: 'Source Code Pro', monospace;font-size:undefined; display: block; white-space: pre; -ms-word-wrap: normal; box-sizing: border-box;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="color: rgb(68, 68, 68); box-sizing: border-box;">define</span> YRWeakObj(o) autoreleasepool{} __weak typeof(o) o##Weak = o;</span>
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#<span class="hljs-keyword" style="color: rgb(68, 68, 68); box-sizing: border-box;">define</span> YRStrongObj(o) autoreleasepool{} __strong typeof(o) o = o##Weak;</span></code><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li><li style="padding: 0px 5px; box-sizing: border-box;">2</li></ul><div class="save_code tracking-ad" style="top: 5px; height: 60px; right: 30px; color: rgb(255, 255, 255); font-size: 14px; display: block; position: absolute; z-index: 2; cursor: pointer; box-sizing: border-box;" data-mod="popu_249"><a target=_blank style="color: rgb(106, 57, 6); text-decoration: none; box-sizing: border-box;" href="javascript:;" target="_blank"><img style="border: currentColor; border-image: none; max-width: 100%; box-sizing: border-box;" src="http://static.blog.youkuaiyun.com/images/save_snippets_01.png" alt="" /></a></div><ul class="pre-numbering" style="list-style: none; margin: 0px; padding: 6px 0px 40px; left: 0px; top: 0px; width: 50px; text-align: right; border-right-color: rgb(221, 221, 221); border-right-width: 1px; border-right-style: solid; position: absolute; box-sizing: border-box; background-color: rgb(238, 238, 238);"><li style="padding: 0px 5px; box-sizing: border-box;">1</li><li style="padding: 0px 5px; box-sizing: border-box;">2</li></ul>
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