blocks|key|1315158|text|正如其他人所指出的，在Cocoa/Objective+C下有许多种"+null“，但需要注意的是，[title+isKindOfClass:NSNull+class]是毫无意义的复杂，因为NSNull+null被记录为一个单例，所以您可以只检查指针是否相等。参见Topics+for+Cocoa:+Using+Null。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1315159|因此，一个好的测试可能是：|1315160|if+(title+==+(id)[NSNull+null]+%7C%7C+title.length+==+0+)+title+=+@"Something";|code-block|syntax|javascript|1315161|请注意，即使标题为nil，title.length也会返回0/nil/false，即本例中的0，因此您不必对其进行特殊处理。这是那些刚接触Objective+C的人很难习惯的东西，特别是来自其他语言的人，在这些语言中，对nil的消息/方法调用崩溃。|1315162|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.apple.com/documentation/Cocoa/Conceptual/NumbersandValues/Articles/Null.html^0|3N|S|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|Z|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|C|$]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

As others have pointed out, there are many kinds of "null" under Cocoa/Objective C. But one further thing to note is that [title isKindOfClass:[NSNull class]] is pointlessly complex since [NSNull null] is documented to be a singleton so you can just check for pointer equality. See <a href="http://developer.apple.com/documentation/Cocoa/Conceptual/NumbersandValues/Articles/Null.html" rel="noreferrer">Topics for Cocoa: Using Null</a>.

So a good test might be:

<pre><code>if (title == (id)[NSNull null] || title.length == 0 ) title = @"Something";
</code></pre>

Note how you can use the fact that even if title is nil, title.length will return 0/nil/false, ie 0 in this case, so you do not have to special case it. This is something that people who are new to Objective C have trouble getting used to, especially coming form other languages where messages/method calls to nil crash.

blocks|key|1317392|text|它就像下面这样简单|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1317393|if([object+length]+>0)
{
++//+do+something
}|code-block|syntax|javascript|1317394|请记住，在目标C中，如果object为null，则返回0作为值。|1317395|这将得到一个空字符串和一个长度为0的字符串。|1317396|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

it is just as simple as

<pre><code>if([object length] &gt;0)
{
 // do something
}
</code></pre>

remember that in objective C if object is null it returns 0 as the value.

This will get you both a null string and a 0 length string.

blocks|key|14606|text|请参阅本网站上的以下相关文章：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|14607|14608|Is+if+(variable)+the+same+as+if+(variable+!=+nil)+in+Objective-C+h|unordered-list-item|offset|length|14609|14610|我认为你的错误与其他事情有关，因为你不应该做额外的检查。|14611|另请参阅此相关问题：Proper+checking+of+nil+sqlite+text+column|14612|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/535120/is-if-variable-the-same-as-if-variable-nil-in-objective-c|1|https://stackoverflow.com/questions/598396/proper-checking-of-nil-sqlite-text-column^0|0|0|0|1S|0|0|0|0|A|15|1|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|X|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|Y|8|@]|9|@$F|Z|G|10|1|11]]|A|$]]|$1|H|3|-4|5|6|7|12|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|13|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|14|8|@]|9|@$F|15|G|16|1|17]]|A|$]]|$1|M|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|N|$O|$5|P|Q|R|A|$S|T]]|U|$5|P|Q|R|A|$S|V]]]]

Refer to the following related articles on this site:

<ul>
<li><a href="https://stackoverflow.com/questions/535120/is-if-variable-the-same-as-if-variable-nil-in-objective-c">Is if (variable) the same as if (variable != nil) in Objective-C</a>
h</li>
</ul>

I think your error is related to something else as you shouldn't need to do the extra checking.

Also see this related question: <a href="https://stackoverflow.com/questions/598396/proper-checking-of-nil-sqlite-text-column">Proper checking of nil sqlite text column</a>

blocks|key|14606|text|我发现，为了真正做到这一点，你最终必须做一些类似的事情|type|unstyled|depth|inlineStyleRanges|entityRanges|data|14607|if+(+(+![myString+isEqual:[NSNull+null]]+)+&&+(+[myString+length]+!=+0+)+)+{
}|code-block|syntax|javascript|14608|否则你会遇到奇怪的情况，控制仍然会绕过你的检查。我还没有遇到一个可以通过isEqual和长度检查的。|offset|length|style|CODE|14609|entityMap^0|0|0|10|7|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I have found that in order to really do it right you end up having to do something similar to 

<pre><code>if ( ( ![myString isEqual:[NSNull null]] ) &amp;&amp; ( [myString length] != 0 ) ) {
}
</code></pre>

Otherwise you get weird situations where control will still bypass your check. I haven't come across one that makes it past the <code>isEqual</code> and length checks.

blocks|key|4120717|text|这些“对我有用的答案”是怎么回事？我们都用同一种语言编码，规则是|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4120718|4120719|确保引用不是nil|ordered-list-item|offset|length|style|BOLD|4120720|Check，并确保字符串的长度不是0|4120721|4120722|这就是对所有人都有效的。如果给定的解决方案只“对您有效”，这只是因为您的应用程序流不允许引用为空或字符串长度为0的场景。正确的方法是使用在所有情况下都能处理所需内容的方法。|4120723|entityMap^0|0|0|6|3|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|R|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|S|8|@$F|T|G|U|H|I]]|9|@]|A|$]]|$1|J|3|K|5|E|7|V|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|P|$]]

Whats with all these "works for me answers" ? We're all coding in the same language and the rules are

<ol>
<li>Ensure the reference isn't nil</li>
<li>Check and make sure the length of the string isn't 0</li>
</ol>

That is what will work for all. If a given solution only "works for you", its only because your application flow won't allow for a scenario where the reference may be null or the string length to be 0. The proper way to do this is the method that will handle what you want in all cases.

blocks|key|14479|text|如果您想测试所有的nil/空对象(如空字符串或空数组/集)，您可以使用以下方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|14480|static+inline+BOOL+IsEmpty(id+object)+{
++++return+object+==+nil
++++++++%7C%7C+([object+respondsToSelector:@selector(length)]
++++++++&&+[(NSData+*)+object+length]+==+0)
++++++++%7C%7C+([object+respondsToSelector:@selector(count)]
++++++++&&+[(NSArray+*)+object+count]+==+0);
}|code-block|syntax|javascript|14481|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|$]]

If you want to test against all nil/empty objects (like empty strings or empty arrays/sets) you can use the following:

<pre><code>static inline BOOL IsEmpty(id object) {
 return object == nil
 || ([object respondsToSelector:@selector(length)]
 &amp;&amp; [(NSData *) object length] == 0)
 || ([object respondsToSelector:@selector(count)]
 &amp;&amp; [(NSArray *) object count] == 0);
}
</code></pre>

blocks|key|902670|text|有两种情况：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|902671|一个对象可能是[NSNull+null]，也可能是不可能的。|offset|length|style|CODE|902672|您的应用程序通常不应该使用[NSNull+null];，只有在想要将“空”对象放入数组中或将其用作字典值时才使用它。然后，您应该知道哪些数组或字典可能包含空值，哪些可能不包含。|902673|如果您认为一个数组从不包含[NSNull+null]值，那么就不要检查它。如果有一个[NSNull+null]，你可能会得到一个异常，但这没问题:+Objective-C异常表示编程错误。并且您有一个编程错误，需要通过更改一些代码来修复。|902674|如果对象可以是[NSNull+null]，那么可以非常简单地通过测试来检查这一点|902675|(object+==+[NSNull+null])。调用isEqual或检查对象的类都是胡说八道。只有一个[NSNull+null]对象，普通的C操作符以最直接和最有效的方式很好地检查它。|902676|如果您检查一个不能为[NSNull+null]的NSString对象(因为您知道它不能为[NSNull+null]，或者因为您刚刚检查了它与[NSNull+null]不同，那么您需要问自己如何处理一个空字符串，即长度为0的字符串。如果您将其视为类似于nil的null字符串，则测试(object.length+==+0)。如果为object+==+nil，则object.length将返回0，因此此测试涵盖nil对象和长度为0的字符串。如果您将长度为0的字符串与nil字符串区别对待，只需检查是否为object+==+nil。|902677|最后，如果您想将字符串添加到数组或字典中，并且字符串可以是nil，则可以选择不添加它，用@""替换它，或者用[NSNull+null]替换它。将其替换为@""意味着您无法区分“无字符串”和“长度为0的字符串”。用[NSNull+null]替换它意味着当您访问检查[NSNull+null]对象的数组或字典时，您必须编写代码。|902678|entityMap^0|0|7|D|0|D|E|0|D|D|16|D|0|7|D|0|0|P|S|7|1H|D|0|A|D|O|8|18|D|1Y|D|3H|3|3L|4|3W|K|4K|D|6Y|D|0|18|3|1I|D|24|3|2Y|D|3N|D|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|W|8|@$D|X|E|Y|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|Z|8|@$D|10|E|11|F|G]]|9|@]|A|$]]|$1|J|3|K|5|6|7|12|8|@$D|13|E|14|F|G]|$D|15|E|16|F|G]]|9|@]|A|$]]|$1|L|3|M|5|6|7|17|8|@$D|18|E|19|F|G]]|9|@]|A|$]]|$1|N|3|O|5|6|7|1A|8|@$D|1B|E|1C|F|G]|$D|1D|E|1E|F|G]|$D|1F|E|1G|F|G]]|9|@]|A|$]]|$1|P|3|Q|5|6|7|1H|8|@$D|1I|E|1J|F|G]|$D|1K|E|1L|F|G]|$D|1M|E|1N|F|G]|$D|1O|E|1P|F|G]|$D|1Q|E|1R|F|G]|$D|1S|E|1T|F|G]|$D|1U|E|1V|F|G]|$D|1W|E|1X|F|G]|$D|1Y|E|1Z|F|G]]|9|@]|A|$]]|$1|R|3|S|5|6|7|20|8|@$D|21|E|22|F|G]|$D|23|E|24|F|G]|$D|25|E|26|F|G]|$D|27|E|28|F|G]|$D|29|E|2A|F|G]]|9|@]|A|$]]|$1|T|3|-4|5|6|7|2B|8|@]|9|@]|A|$]]]|U|$]]

There are two situations:

It is possible that an object is <code>[NSNull null]</code>, or it is impossible. 
 Your application usually shouldn't use <code>[NSNull null];</code> you only use it if you want to put a "null" object into an array, or use it as a dictionary value. And then you should know which arrays or dictionaries might contain null values, and which might not. 
 If you think that an array never contains <code>[NSNull null]</code> values, then don't check for it. If there is an <code>[NSNull null]</code>, you might get an exception but that is fine: Objective-C exceptions indicate programming errors. And you have a programming error that needs fixing by changing some code. 

If an object could be <code>[NSNull null]</code>, then you check for this quite simply by testing 
 <code>(object == [NSNull null])</code>. Calling <code>isEqual</code> or checking the class of the object is nonsense. There is only one <code>[NSNull null]</code> object, and the plain old C operator checks for it just fine in the most straightforward and most efficient way. 

If you check an <code>NSString</code> object that cannot be <code>[NSNull null]</code> (because you know it cannot be <code>[NSNull null]</code> or because you just checked that it is different from <code>[NSNull null]</code>, then you need to ask yourself how you want to treat an empty string, that is one with length 0. If you treat it is a <code>null</code> string like <code>nil</code>, then test <code>(object.length == 0)</code>. object.length will return 0 if <code>object == nil</code>, so this test covers nil objects and strings with length 0. If you treat a string of length 0 different from a nil string, just check if <code>object == nil</code>. 

Finally, if you want to add a string to an array or a dictionary, and the string could be nil, you have the choice of not adding it, replacing it with <code>@""</code>, or replacing it with <code>[NSNull null]</code>. Replacing it with <code>@""</code> means you lose the ability to distinguish between "no string" and "string of length 0". Replacing it with <code>[NSNull null]</code> means you have to write code when you access the array or dictionary that checks for <code>[NSNull null]</code> objects.

blocks|key|4120915|text|您只需检查是否为空|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4120916|if(data[@"Bonds"]==nil){
++NSLog(@"it+is+nil");
}|code-block|syntax|javascript|4120917|或|4120918|if+([data[@"Bonds"]+isKindOfClass:[NSNull+class]])+{
++++NSLog(@"it+is+null");
}|4120919|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

You just check for nil

<pre><code>if(data[@"Bonds"]==nil){
 NSLog(@"it is nil");
}
</code></pre>

or

<pre><code>if ([data[@"Bonds"] isKindOfClass:[NSNull class]]) {
 NSLog(@"it is null");
}
</code></pre>

blocks|key|1317625|text|宏观解决方案(2020)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1317626|下面是我用于安全字符串的宏，而不是在上获取"(null)“字符串的示例：|offset|length|style|BOLD|1317627|#define+SafeString(STRING)+([STRING+length]+==+0+?+@""+:+STRING)|code-block|syntax|javascript|1317628|假设您有一个成员类和name属性，并且name为nil：|1317629|NSLog(@"%25@",+member.name);+//+prints+(null)+on+UILabel|1317630|使用宏：|1317631|NSLog(@"%25@",+SafeString(member.name));+//+prints+empty+string+on+UILabel|1317632|又好又干净|1317633|扩展解决方案(2020)|1317634|如果你喜欢在你的项目中检查nil+Null和空字符串，你可以使用下面的扩展行：|1317635|NSString%2BExtension.h|1317636|///
///+Checks+if+giving+String+is+an+empty+string+or+a+nil+object+or+a+Null.
///+@param+string+string+value+to+check.
///
%2B+(BOOL)isNullOrEmpty:(NSString*)string;|1317637|NSString%2BExtension.m|1317638|%2B+(BOOL)isNullOrEmpty:(NSString*)string+{
++++if+(string)+{+//+is+not+Nil
++++++++NSRange+range+=+[string+rangeOfString:string];
++++++++BOOL+isEmpty+=+(range.length+<=+0+%7C%7C+[string+isEqualToString:@"+"]);
++++++++BOOL+isNull+=+string+==+(id)[NSNull+null];

++++++++return+(isNull+%7C%7C+isEmpty);
++++}

++++return+YES;
}|1317639|示例用法|1317640|if+(![NSString+isNullOrEmpty:someTitle])+{
++++//+You+can+safely+use+on+a+Label+or+even+add+in+an+Array+for+example.+Remember:+Arrays+don't+like+the+nil+values!
}|1317641|entityMap^0|0|M|6|0|0|0|0|0|0|0|0|0|0|K|0|0|0|K|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1E|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1F|8|@$D|1G|E|1H|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|1I|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|1J|8|@]|9|@]|A|$]]|$1|O|3|P|5|J|7|1K|8|@]|9|@]|A|$K|L]]|$1|Q|3|R|5|6|7|1L|8|@]|9|@]|A|$]]|$1|S|3|T|5|J|7|1M|8|@]|9|@]|A|$K|L]]|$1|U|3|V|5|6|7|1N|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1O|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|1P|8|@]|9|@]|A|$]]|$1|10|3|11|5|6|7|1Q|8|@$D|1R|E|1S|F|G]]|9|@]|A|$]]|$1|12|3|13|5|J|7|1T|8|@]|9|@]|A|$K|L]]|$1|14|3|15|5|6|7|1U|8|@$D|1V|E|1W|F|G]]|9|@]|A|$]]|$1|16|3|17|5|J|7|1X|8|@]|9|@]|A|$K|L]]|$1|18|3|19|5|6|7|1Y|8|@]|9|@]|A|$]]|$1|1A|3|1B|5|J|7|1Z|8|@]|9|@]|A|$K|L]]|$1|1C|3|-4|5|6|7|20|8|@]|9|@]|A|$]]]|1D|$]]

<h1>MACRO Solution (2020)</h1>

Here is the macro that I use for safe string instead of getting "(null)" string on a <a href="https://developer.apple.com/documentation/uikit/uilabel" rel="nofollow noreferrer">UILabel</a> for example:

<pre><code>#define SafeString(STRING) ([STRING length] == 0 ? @"" : STRING)
</code></pre>

let say you have an member class and name property, and name is nil:

<pre><code>NSLog(@"%@", member.name); // prints (null) on UILabel
</code></pre>

with macro:

<pre><code>NSLog(@"%@", SafeString(member.name)); // prints empty string on UILabel
</code></pre>

nice and clean 

<h1>Extension Solution (2020)</h1>

If you prefer checking nil Null and empty string in your project you can use my extension line below:

NSString+Extension.h

<pre><code>///
/// Checks if giving String is an empty string or a nil object or a Null.
/// @param string string value to check.
///
+ (BOOL)isNullOrEmpty:(NSString*)string;
</code></pre>

NSString+Extension.m

<pre><code>+ (BOOL)isNullOrEmpty:(NSString*)string {
 if (string) { // is not Nil
 NSRange range = [string rangeOfString:string];
 BOOL isEmpty = (range.length &lt;= 0 || [string isEqualToString:@" "]);
 BOOL isNull = string == (id)[NSNull null];

 return (isNull || isEmpty);
 }

 return YES;
}
</code></pre>

<h3>Example Usage</h3>

<pre><code>if (![NSString isNullOrEmpty:someTitle]) {
 // You can safely use on a Label or even add in an Array for example. Remember: Arrays don't like the nil values!
}
</code></pre>

blocks|key|902558|text|if(textfield.text.length+==+0){
+++//do+your+desired+work
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|902559|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>if(textfield.text.length == 0){
 //do your desired work
}
</code></pre>

blocks|key|1315306|text|尝试使用此命令检查null|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1315307|+if+(text+==+nil)|code-block|syntax|javascript|1315308|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|$]]

Try this for check null

<pre><code> if (text == nil)
</code></pre>

blocks|key|1315349|text|@interface+NSString+(StringFunctions)
-+(BOOL)+hasCharacters;
@end

@implementation+NSString+(StringFunctions)
-+(BOOL)+hasCharacters+{
++++if(self+==+(id)[NSNull+null])+{
++++++++return+NO;
++++}else+{
++++++++if([self+length]+==+0)+{
++++++++++++return+NO;
++++++++}
++++}
++++return+YES;
}
@end

NSString+*strOne+=+nil;
if([strOne+hasCharacters])+{
++++NSLog(@"%25@",strOne);
}else+{
++++NSLog(@"String+is+Empty");
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1315350|这将适用于以下情况：NSString+*strOne+=+@""、NSString+*strOne+=+@"StackOverflow"、NSString+*strOne+=+[NSNull+null]或NSString+*strOne。|unstyled|offset|length|style|CODE|1315351|entityMap^0|0|A|M|X|Z|1X|W|2U|G|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|N|8|@$G|O|H|P|I|J]|$G|Q|H|R|I|J]|$G|S|H|T|I|J]|$G|U|H|V|I|J]]|9|@]|A|$]]|$1|K|3|-4|5|F|7|W|8|@]|9|@]|A|$]]]|L|$]]

<pre><code>@interface NSString (StringFunctions)
- (BOOL) hasCharacters;
@end

@implementation NSString (StringFunctions)
- (BOOL) hasCharacters {
 if(self == (id)[NSNull null]) {
 return NO;
 }else {
 if([self length] == 0) {
 return NO;
 }
 }
 return YES;
}
@end

NSString *strOne = nil;
if([strOne hasCharacters]) {
 NSLog(@"%@",strOne);
}else {
 NSLog(@"String is Empty");
}
</code></pre>

This would work with the following cases, <code>NSString *strOne = @""</code> OR <code>NSString *strOne = @"StackOverflow"</code> OR <code>NSString *strOne = [NSNull null]</code> OR <code>NSString *strOne</code>.

blocks|key|902298|text|如果这类东西还不存在，您可以创建一个NSString类别：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|902299|@interface+NSString+(TrucBiduleChoseAdditions)

-+(BOOL)isEmpty;

@end

@implementation+NSString+(TrucBiduleChoseAdditions)

-+(BOOL)isEmpty+{
++++return+self+==+nil+%7C%7C+[@""+isEqualToString:self];
}

@end|code-block|syntax|javascript|902300|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|$]]

If that kind of thing does not already exist, you can make an NSString category:

<pre><code>@interface NSString (TrucBiduleChoseAdditions)

- (BOOL)isEmpty;

@end

@implementation NSString (TrucBiduleChoseAdditions)

- (BOOL)isEmpty {
 return self == nil || [@"" isEqualToString:self];
}

@end
</code></pre>

blocks|key|4120649|text|对我有效的是if+(+!myobject++)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4120650|entityMap^0|6|H|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|$]]

What works for me is <code>if ( !myobject )</code>

blocks|key|1315371|text|我只用检查空字符串|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1315372|1315373|+if+([myString+if：NSNull+null])|blockquote|1315374|1315375|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|J|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|K|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|L|8|@]|9|@]|A|$]]|$1|G|3|-4|5|6|7|M|8|@]|9|@]|A|$]]]|H|$]]

I only check null string with

<blockquote>
 if ([myString isEqual:[NSNull null]])
</blockquote>

blocks|key|14823|text|if+([linkedStr+isEqual:(id)[NSNull+null]])
++++++++++++++++{
++++++++++++++++++++_linkedinLbl.text=@"No";
++++++++++++++++}else{
++++++++++++++++++++_linkedinLbl.text=@"Yes";
++++++++++++++++}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|14824|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>if ([linkedStr isEqual:(id)[NSNull null]])
 {
 _linkedinLbl.text=@"No";
 }else{
 _linkedinLbl.text=@"Yes";
 }
</code></pre>

blocks|key|4120977|text|if+([strpass+isEqual:[NSNull+null]]+%7C%7C+strpass==nil+%7C%7C+[strpass+isEqualToString:@"<null>"]+%7C%7C+[strpass+isEqualToString:@"(null)"]+%7C%7C+strpass.length==0+%7C%7C+[strpass+isEqualToString:@""])
{
++++//string+is+blank++
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|4120978|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>if ([strpass isEqual:[NSNull null]] || strpass==nil || [strpass isEqualToString:@"&lt;null&gt;"] || [strpass isEqualToString:@"(null)"] || strpass.length==0 || [strpass isEqualToString:@""])
{
 //string is blank 
}
</code></pre>

blocks|key|902866|text|对于字符串：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|902867|%2B+(BOOL)+checkStringIsNotEmpty:(NSString*)string+{
if+(string+==+nil+%7C%7C+string.length+==+0)+return+NO;
return+YES;|code-block|syntax|javascript|902868|}|902869|请参考下图：|902870|​|902871|📷|atomic|offset|length|902872|902873|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/03b40ad83c2aa46eb44d20c30d289b0e.png|imageAlt^0|0|0|0|0|0|0|1|0|0|0^^$0|@$1|2|3|4|5|6|7|11|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|12|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|13|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|14|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|15|8|@]|9|@]|A|$]]|$1|M|3|N|5|O|7|16|8|@]|9|@$P|17|Q|18|1|19]]|A|$]]|$1|R|3|L|5|6|7|1A|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|T|$U|$5|V|W|X|A|$Y|Z|10|-4]]]]

For string:

<pre><code>+ (BOOL) checkStringIsNotEmpty:(NSString*)string {
if (string == nil || string.length == 0) return NO;
return YES;
</code></pre>

}

Refer the picture below:

<a href="https://i.stack.imgur.com/0YXrx.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0YXrx.png" alt="enter image description here"></a>

blocks|key|4121054|text|对于字符串：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4121055|%2B+(BOOL)+checkStringIsNotEmpty:(NSString*)string+{
if+(string+==+nil+%7C%7C+string.length+==+0)+return+NO;
return+YES;}|code-block|syntax|javascript|4121056|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|$]]

For string:

<pre><code>+ (BOOL) checkStringIsNotEmpty:(NSString*)string {
if (string == nil || string.length == 0) return NO;
return YES;}
</code></pre>

I was using this in my iPhone app

<pre><code>if (title == nil) {
 // do something
}
</code></pre>

but it throws some exception, and the console shows that the title is "(null)".

So I'm using this now:

<pre><code>if (title == nil || [title isKindOfClass:[NSNull class]]) {
 //do something
}
</code></pre>

What is the difference, and what is the best way to determine whether a string is null?

What is the right way to check for a null string in Objective-C?

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文章&问答评论现已支持表情

我在我的iPhone应用程序中使用了这个if (title == nil) {    // do something}但是它抛出了一些异常，控制台显示标题是"(null)“。所以我现在使用这个：if (title == nil || [title isKindOfClass:[NSNull class]]) {    //do something}有什么区别，确定字符串是否为空的最佳方法是什么？

问在Objective-C中检查空字符串的正确方法是什么？
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问在Objective-C中检查空字符串的正确方法是什么？
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