blocks|key|4380717|text|字符串总是复制到Objective-C中，所以第二个选项很可能是创建另一个字符串，然后指向它。从那方面来说，我认为你是对的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4380718|为了扮演魔鬼的倡导者，我假设编译器会优化选项B，以执行类似选项A的操作。就我个人而言，我总是选择选项B，因为就您想要完成的最终操作而言，它更具可读性。|4380719|更新:我没有找到以不同的方式实现你的目标的方法，但你可能会对这个花边新闻感兴趣(来自Apple+UITextField+Docs)：|offset|length|4380720|4380721|+clearButtonMode|blockquote|4380722|4380723|控制标准清除按钮何时出现在文本字段中。|4380724|@property(非原子)+UITextFieldViewMode+clearButtonMode|4380725|讨论|4380726|标准的清除按钮显示在文本字段的右侧，作为用户快速删除文本的一种方式。此按钮将根据为此属性设置的值自动显示。|4380727|此属性的默认值为UITextFieldViewModeNever。|4380728|4380729|我认为这将允许您为用户设置清除文本字段的功能。|4380730|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.apple.com/iphone/library/documentation/UIKit/Reference/UITextField_Class/Reference/UITextField.html#//apple_ref/occ/instp/UITextField/clearButtonMode^0|0|0|16|M|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|17|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|18|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|19|8|@]|9|@$F|1A|G|1B|1|1C]]|A|$]]|$1|H|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]|$1|I|3|J|5|K|7|1E|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|1G|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|1H|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1I|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|1J|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|1K|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|1L|8|@]|9|@]|A|$]]|$1|X|3|Y|5|6|7|1M|8|@]|9|@]|A|$]]|$1|Z|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]]|10|$11|$5|12|13|14|A|$15|16]]]]

Strings always copy in Objective-C, so the second option is most likely creating another string, and then pointing to it. In that way, I think you're right.

To play devil's advocate, I would assume that the compiler optimizes option B to do something like option A anyway. Personally, I would always do option B because it's more readable as far as the end operation you want to accomplish.

UPDATE: I didn't find a way to accomplish your goal differently, but you may be interested in this tidbit (from <a href="http://developer.apple.com/iphone/library/documentation/UIKit/Reference/UITextField_Class/Reference/UITextField.html#//apple_ref/occ/instp/UITextField/clearButtonMode" rel="nofollow noreferrer">Apple UITextField Docs</a>):

<blockquote>
 clearButtonMode
 
 Controls when the standard clear
 button appears in the text field.
 
 @property(nonatomic)
 UITextFieldViewMode clearButtonMode
 
 Discussion
 
 The standard clear button is displayed
 at the right side of the text field as
 a way for the user to remove text
 quickly. This button appears
 automatically based on the value set
 for this property.
 
 The default value for this property is
 UITextFieldViewModeNever.
</blockquote>

I think this would allow you to setup functionality for the user to clear the text field.

blocks|key|145252|text|为了清楚起见，我通常使用textFieldX.text+=+@"";。这帮助我记住，值应该是一个字符串，并且我可以传递所有标准的字符串方法。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|145253|entityMap^0|C|M|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

I usually do <code>textFieldX.text = @"";</code> just for clarity. This helps me remember that the value should be a string, and that I can pass it all the standard string methods.

blocks|key|1164224|text|就我个人而言，我会少考虑内存使用，而更多地考虑代码的可维护性。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1164225|对我来说，标签总是有一个字符串是有意义的。将来有人可能会尝试附加一个labes值，将其保存在数据库中，将其包装在xml中，等等。在这种情况下，一个空的NSString对我来说比0x0更有意义。|1164226|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Personally I would think less of the memory usage here and more on code-maintainability.

To me, It makes sense that a label always has a string. In the future someone might try to append a labels value, save it in a database, wrap it in xml, etc. An empty NSString in this case makes much more sense to me that a 0x0.

blocks|key|144423|text|我建议您使用nil，因为我发现当您使用@"“时，占位符不会居中对齐(如果它必须对齐)。请看，我是如何更改代码以正确对齐占位符的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|144424|+wordTextField.textAlignment+=+UITextAlignmentCenter;
+//wordTextField.text+=+@"";
+wordTextField.text+=+nil;
+translationTextField.textAlignment+=+UITextAlignmentCenter;
+//translationTextField.text+=+@"";
+translationTextField.text+=+nil;|code-block|syntax|javascript|144425|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I recommend you to use nil, because I discovered that when you use @"", the placeholder is not aligned in the center(if it must be aligned). Look, how I changed my code to get placeholder aligned properly. 

<pre><code> wordTextField.textAlignment = UITextAlignmentCenter;
 //wordTextField.text = @"";
 wordTextField.text = nil;
 translationTextField.textAlignment = UITextAlignmentCenter;
 //translationTextField.text = @"";
 translationTextField.text = nil;
</code></pre>

blocks|key|1444853|text|我发现使用textField.text+=+nil;对我的项目产生了不良影响。我正在做一个计算器。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1444854|当使用上面的代码时，在我按下清除按钮后，按下数字不会出现在屏幕上。|1444855|textField.text+=+@"";+|code-block|syntax|javascript|1444856|对我来说很好。|1444857|entityMap^0|5|L|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|U|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|V|8|@]|D|@]|E|$]]|$1|O|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|P|$]]

I find that using <code>textField.text = nil;</code> has an undesirable effect on my project. I am building a calculator.

When using the above code, after I press the clear button, pressing a digit does not come up on screen. 

<pre><code>textField.text = @""; 
</code></pre>

works good for me.

For an <code>IBOutlet UITextField</code>, does it matter as far as memory management or other reasons how you clear the text value?

<pre><code>textFieldX.text = nil
</code></pre>

or

<pre><code>textFieldX.text = @"";
</code></pre>

In objective-c it is acceptable to message a <code>nil</code> object and <code>@""</code> is a static <code>NSString *</code>. I'm not sure if every <code>@""</code> points to the same object in memory or if it allocates a bunch of 1 byte null terminated strings.

Not a big deal, just thought I'd ask the community. Thanks.

Best way to clear a UITextField

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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对于IBOutlet UITextField，清除文本值的方式是否与内存管理或其他原因有关？textFieldX.text = nil或textFieldX.text = @"";在objective-c中，消息传递nil对象是可接受的，而@""是静态NSString *。我不确定是否每个@""都指向内存中的同一个对象...

问清除UITextField的最佳方法
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