blocks|key|1130994|text|一个集合有几个用例。您可以枚举(例如，使用enumerateObjectsUsingBlock或NSFastEnumeration)，调用containsObject来测试成员资格，使用anyObject获取成员(不是随机的)，或者使用allObjects将其转换为数组(没有特定的顺序)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1130995|当你不想要重复的，不关心顺序的，并且想要快速的成员测试时，set是合适的。|1130996|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSSet_Class/Reference/Reference.html#//apple_ref/doc/uid/20000143-SW21|1|http://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSSet_Class/Reference/Reference.html#//apple_ref/doc/uid/20000143-CIHCDHBD|2|http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSSet_Class/Reference/Reference.html#//apple_ref/doc/uid/20000143-CHDCCAAI|3|http://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSSet_Class/Reference/Reference.html#//apple_ref/doc/uid/20000143-CHDDFHBE^0|L|Q|1X|E|2L|9|3A|A|L|Q|0|1X|E|1|2L|9|2|3A|A|3|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@$9|14|A|15|1|16]|$9|17|A|18|1|19]|$9|1A|A|1B|1|1C]|$9|1D|A|1E|1|1F]]|E|$]]|$1|F|3|G|5|6|7|1G|8|@]|D|@]|E|$]]|$1|H|3|-4|5|6|7|1H|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]|P|$5|K|L|M|E|$N|Q]]|R|$5|K|L|M|E|$N|S]]|T|$5|K|L|M|E|$N|U]]]]

There are several use cases for a set. You could enumerate through (e.g. with <a href="https://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSSet_Class/Reference/Reference.html#//apple_ref/doc/uid/20000143-SW21" rel="noreferrer"><code>enumerateObjectsUsingBlock</code></a> or NSFastEnumeration), call <a href="http://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSSet_Class/Reference/Reference.html#//apple_ref/doc/uid/20000143-CIHCDHBD" rel="noreferrer"><code>containsObject</code></a> to test for membership, use <a href="http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSSet_Class/Reference/Reference.html#//apple_ref/doc/uid/20000143-CHDCCAAI" rel="noreferrer"><code>anyObject</code></a> to get a member (not random), or convert it to an array (in no particular order) with <a href="http://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSSet_Class/Reference/Reference.html#//apple_ref/doc/uid/20000143-CHDDFHBE" rel="noreferrer"><code>allObjects</code></a>.

A set is appropriate when you don't want duplicates, don't care about order, and want fast membership testing.

blocks|key|1131022|text|NSSet没有objectAtIndex方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1131023|尝试调用allObjects，它将返回所有对象的NSArray。|1131024|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|$]]

NSSet doesn't have a method objectAtIndex:

Try calling allObjects which returns an NSArray of all the objects.

blocks|key|1131185|text|如果您有某种唯一标识符来选择所需的对象，则可以使用filteredSetUsingPredicate。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1131186|首先创建谓词(假设您在对象中的唯一id称为“NSString”，并且它是一个标识符)：|1131187|NSPredicate+*myPredicate+=+[NSPredicate+predicateWithFormat:@"identifier+==+%25@",+identifier];|code-block|syntax|javascript|1131188|然后使用谓词选择对象：|1131189|NSObject+*myChosenObject+=+[mySet+filteredSetUsingPredicate:myPredicate].anyObject;|1131190|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

it is possible to use filteredSetUsingPredicate if you have some kind of unique identifier to select the object you need.

First create the predicate (assuming your unique id in the object is called "identifier" and it is an NSString):

<pre><code>NSPredicate *myPredicate = [NSPredicate predicateWithFormat:@"identifier == %@", identifier];
</code></pre>

And then choose the object using the predicate:

<pre><code>NSObject *myChosenObject = [mySet filteredSetUsingPredicate:myPredicate].anyObject;
</code></pre>

blocks|key|916348|text|NSArray+*myArray+=+[myNSSet+allObjects];|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|916349|MyObject+*object+=+[myArray+objectAtIndex:(NSUInteger+*)]|code-block|syntax|javascript|916350|将NSUInteger替换为所需对象的索引。|916351|entityMap^0|0|14|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

<code>NSArray *myArray = [myNSSet allObjects];</code>

<pre><code>MyObject *object = [myArray objectAtIndex:(NSUInteger *)]
</code></pre>

replace NSUInteger with the index of your desired object.

blocks|key|916460|text|对于Swift3和iOS10：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|916461|//your+current+set
let+mySet+:+NSSet
//targetted+index
let+index+:+Int
//get+object+in+set+at+index
let+object+=+mySet.allObjects[index]|code-block|syntax|javascript|916462|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 Swift3 &amp; iOS10 :

<pre><code>//your current set
let mySet : NSSet
//targetted index
let index : Int
//get object in set at index
let object = mySet.allObjects[index]
</code></pre>

blocks|key|916303|text|NSSet使用方法isEqual：(除了散列方法外，放入该集合中的对象必须覆盖该方法)来确定对象是否在其中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|916304|因此，例如，如果您有一个通过id值定义其唯一性的数据模型(假设属性为：|916305|@property+NSUInteger+objectID;|code-block|syntax|javascript|916306|然后将isEqual:实现为|916307|-+(BOOL)isEqual:(id)object
{
++return+(self.objectID+==+[object+objectID]);
}|916308|你可以实现哈希：|916309|-+(NSUInteger)hash
{
+return+self.objectID;++//+to+be+honest,+I+just+do+what+Apple+tells+me+to+here
+++++++++++++++++++++++//+because+I've+forgotten+how+Sets+are+implemented+under+the+hood
}|916310|然后，您可以使用以下命令获取具有该ID的对象(以及检查它是否在NSSet中)：|916311|MyObject+*testObject+=+[[MyObject+alloc]+init];
testObject.objectID+=+5;+//+for+example.++

//+I+presume+your+object+has+more+properties+which+you+don't+need+to+set+here+
//+because+it's+objectID+that+defines+uniqueness+(see+isEqual:+above)

MyObject+*existingObject+=+[mySet+member:+testObject];

//+now+you've+either+got+it+or+existingObject+is+nil|916312|但是的，从NSSet中获得某些东西的唯一方法是首先考虑定义其唯一性的东西。|916313|我还没有测试哪种方法更快，但我避免使用枚举，因为它可能是线性的，而使用member:方法会快得多。这是优先使用NSSet而不是NSArray的原因之一。|916314|entityMap^0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|11|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|13|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|15|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|16|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|17|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|18|8|@]|9|@]|A|$G|H]]|$1|U|3|V|5|6|7|19|8|@]|9|@]|A|$]]|$1|W|3|X|5|6|7|1A|8|@]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|Z|$]]

NSSet uses the method isEqual: (which the objects you put into that set must override, in addition, the hash method) to determine if an object is inside of it.

So, for example if you have a data model that defines its uniqueness by an id value (say the property is:

<pre><code>@property NSUInteger objectID;
</code></pre>

then you'd implement isEqual: as

<pre><code>- (BOOL)isEqual:(id)object
{
 return (self.objectID == [object objectID]);
}
</code></pre>

and you could implement hash:

<pre><code>- (NSUInteger)hash
{
 return self.objectID; // to be honest, I just do what Apple tells me to here
 // because I've forgotten how Sets are implemented under the hood
}
</code></pre>

Then, you can get an object with that ID (as well as check for whether it's in the NSSet) with:

<pre><code>MyObject *testObject = [[MyObject alloc] init];
testObject.objectID = 5; // for example. 

// I presume your object has more properties which you don't need to set here 
// because it's objectID that defines uniqueness (see isEqual: above)

MyObject *existingObject = [mySet member: testObject];

// now you've either got it or existingObject is nil
</code></pre>

But yeah, the only way to get something out of a NSSet is by considering that which defines its uniqueness in the first place.

I haven't tested what's faster, but I avoid using enumeration because that might be linear whereas using the member: method would be much faster. That's one of the reasons to prefer the use of NSSet instead of NSArray.

blocks|key|1131194|text|for+(id+currentElement+in+mySet)
{
++++//+**+some+actions+with+currentElement+
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1131195|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>for (id currentElement in mySet)
{
 // ** some actions with currentElement 
}
</code></pre>

If you can't get an object with objectAtIndex: from an NSSet then how do you retrieve objects?

Getting an object from an NSSet

如果不能使用objectAtIndex:从NSSet获取对象，那么如何检索对象呢？

问从NSSet获取对象
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