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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