blocks|key|1277394|text|这里有一个快速而粗糙的实现。还没有经过测试。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1277395|NSString+*letters+=+@"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

-(NSString+*)+randomStringWithLength:+(int)+len+{

++++NSMutableString+*randomString+=+[NSMutableString+stringWithCapacity:+len];

++++for+(int+i=0;+i<len;+i%2B%2B)+{
+++++++++[randomString+appendFormat:+@"%25C",+[letters+characterAtIndex:+arc4random_uniform([letters+length])]];
++++}

++++return+randomString;
}|code-block|syntax|javascript|1277396|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|$]]

Here's a quick and dirty implementation. Hasn't been tested.

<pre><code>NSString *letters = @"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

-(NSString *) randomStringWithLength: (int) len {

 NSMutableString *randomString = [NSMutableString stringWithCapacity: len];

 for (int i=0; i&lt;len; i++) {
 [randomString appendFormat: @"%C", [letters characterAtIndex: arc4random_uniform([letters length])]];
 }

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

blocks|key|1277617|text|不完全是你想要的，但还是有用的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1277618|[[NSProcessInfo+processInfo]+globallyUniqueString]|code-block|syntax|javascript|1277619|示例输出：|1277620|450FEA63-2286-4B49-8ACC-9822C7D4356B-1376-00000239A4AC4FD5|1277621|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|$]]

Not exactly what you ask, but still useful:

<pre><code>[[NSProcessInfo processInfo] globallyUniqueString]
</code></pre>

Sample output:

<pre><code>450FEA63-2286-4B49-8ACC-9822C7D4356B-1376-00000239A4AC4FD5
</code></pre>

blocks|key|1277456|text|NSString+*alphabet++=+@"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXZY0123456789";
NSMutableString+*s+=+[NSMutableString+stringWithCapacity:20];
for+(NSUInteger+i+=+0U;+i+<+20;+i%2B%2B)+{
++++u_int32_t+r+=+arc4random()+%25+[alphabet+length];
++++unichar+c+=+[alphabet+characterAtIndex:r];
++++[s+appendFormat:@"%25C",+c];
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1277457|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>NSString *alphabet = @"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXZY0123456789";
NSMutableString *s = [NSMutableString stringWithCapacity:20];
for (NSUInteger i = 0U; i &lt; 20; i++) {
 u_int32_t r = arc4random() % [alphabet length];
 unichar c = [alphabet characterAtIndex:r];
 [s appendFormat:@"%C", c];
}
</code></pre>

blocks|key|1277568|text|当然，你可以让它变得更短：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1277569|%2B(NSString*)generateRandomString:(int)num+{
++++NSMutableString*+string+=+[NSMutableString+stringWithCapacity:num];
++++for+(int+i+=+0;+i+<+num;+i%2B%2B)+{
++++++++[string+appendFormat:@"%25C",+(unichar)('a'+%2B+arc4random_uniform(26))];
++++}
++++return+string;
}|code-block|syntax|javascript|1277570|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|$]]

Surely you can make this shorter:

<pre><code>+(NSString*)generateRandomString:(int)num {
 NSMutableString* string = [NSMutableString stringWithCapacity:num];
 for (int i = 0; i &lt; num; i++) {
 [string appendFormat:@"%C", (unichar)('a' + arc4random_uniform(26))];
 }
 return string;
}
</code></pre>

blocks|key|1062954|text|如果您愿意将自己限制为只能使用十六进制字符，那么最简单的选择是生成一个UUID：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1062955|NSString+*uuid+=+[NSUUID+UUID].UUIDString;|code-block|syntax|javascript|1062956|输出示例：16E3DF0B-87B3-4162-A1A1-E03DB2F59654。|offset|length|style|CODE|1062957|如果你想要一个较小的随机字符串，那么你可以只抓取前8个字符。|1062958|它是一个版本4的UUID，这意味着第三个和第四个组中的第一个字符不是随机的(它们总是4和8，9，A或B中的一个)。|1062959|字符串中的每个字符都是完全随机的，您可以在数百年内每秒生成数百万个UUID，而不会有两次生成相同UUID的风险。|1062960|entityMap^0|0|0|5|10|0|0|16|1|18|1|1A|1|1C|1|1E|1|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@$I|X|J|Y|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|Z|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|10|8|@$I|11|J|12|K|L]|$I|13|J|14|K|L]|$I|15|J|16|K|L]|$I|17|J|18|K|L]|$I|19|J|1A|K|L]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1B|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]]|T|$]]

If you're willing to limit yourself to hex characters only, then the simplest option is to generate a UUID:

<pre><code>NSString *uuid = [NSUUID UUID].UUIDString;
</code></pre>

Example output: <code>16E3DF0B-87B3-4162-A1A1-E03DB2F59654</code>.

If you want a smaller random string then you can grab just the first 8 characters.

It's a version 4 UUID which means the first character in the 3rd and 4th group is not random (they will always be <code>4</code> and one of <code>8</code>, <code>9</code>, <code>A</code> or <code>B</code>).

Every other character in the string is fully random and you can generate millions of UUIDs every second for hundreds of years without much risk of the same UUID being generated twice.

blocks|key|1062805|text|Jeff+B答案的类别版本。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1062806|NSString%2BRandom.h|1062807|#import+<Foundation/Foundation.h>

@interface+NSString+(Random)

%2B+(NSString+*)randomAlphanumericStringWithLength:(NSInteger)length;

@end|code-block|syntax|javascript|1062808|NSString%2BRandom.m|1062809|#import+"NSString%2BRandom.h"

+@implementation+NSString+(Random)

%2B+(NSString+*)randomAlphanumericStringWithLength:(NSInteger)length
{+
++++NSString+*letters+=+@"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
++++NSMutableString+*randomString+=+[NSMutableString+stringWithCapacity:length];

++++for+(int+i+=+0;+i+<+length;+i%2B%2B)+{
++++++++[randomString+appendFormat:@"%25C",+[letters+characterAtIndex:arc4random()+%25+[letters+length]]];
++++}

++++return+randomString;
}

@end|1062810|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|$]]

A category version of Jeff B's answer.

NSString+Random.h

<pre><code>#import &lt;Foundation/Foundation.h&gt;

@interface NSString (Random)

+ (NSString *)randomAlphanumericStringWithLength:(NSInteger)length;

@end
</code></pre>

NSString+Random.m

<pre><code>#import "NSString+Random.h"

 @implementation NSString (Random)

+ (NSString *)randomAlphanumericStringWithLength:(NSInteger)length
{ 
 NSString *letters = @"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 NSMutableString *randomString = [NSMutableString stringWithCapacity:length];

 for (int i = 0; i &lt; length; i++) {
 [randomString appendFormat:@"%C", [letters characterAtIndex:arc4random() % [letters length]]];
 }

 return randomString;
}

@end
</code></pre>

blocks|key|1277453|text|您也可以只生成一个UUID。虽然不是真正的随机，但它们是复杂和独特的，这使得它们在大多数用途中看起来是随机的。生成一个字符串，然后获取与传递的长度相等的字符范围。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1277454|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

You could also just generate a UUID. While not truly random, they are complex and unique which makes them appear random for most uses. Generate one as a string and then take a range of characters equal to the passed length.

blocks|key|1277942|text|斯威夫特|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1277943|func+randomStringWithLength(length:+Int)+->+String+{
++++let+alphabet+=+"-_1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
++++let+upperBound+=+UInt32(count(alphabet))
++++return+String((0..<length).map+{+_+->+Character+in
++++++++return+alphabet[advance(alphabet.startIndex,+Int(arc4random_uniform(upperBound)))]
++++})
}|code-block|syntax|javascript|1277944|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|$]]

Swift

<pre><code>func randomStringWithLength(length: Int) -&gt; String {
 let alphabet = "-_1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
 let upperBound = UInt32(count(alphabet))
 return String((0..&lt;length).map { _ -&gt; Character in
 return alphabet[advance(alphabet.startIndex, Int(arc4random_uniform(upperBound)))]
 })
}
</code></pre>

blocks|key|1062761|text|这里有一种不同的方法来解决它。您可以在整数和字符之间进行转换，并生成要选择的动态字符列表，而不是使用准备好的字符串。它相当精简和快速，但有更多的代码。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1062762|int+charNumStart+=+(int)+'0';
int+charNumEnd+=+(int)+'9';
int+charCapitalStart+=+(int)+'A';
int+charCapitalEnd+=+(int)+'Z';
int+charLowerStart+=+(int)+'a';
int+charLowerEnd+=+(int)+'z';

int+amountOfChars+=+(charNumEnd+-+charNumStart)+%2B+(charCapitalEnd+-+charCapitalStart)+%2B+(charLowerEnd+-+charLowerStart);+//+amount+of+the+characters+we+want.
int+firstGap+=+charCapitalStart+-+charNumEnd;+//+there+are+gaps+of+random+characters+between+numbers+and+uppercase+letters,+so+this+allows+us+to+skip+those.
int+secondGap+=+charLowerStart+-+charCapitalEnd;+//+similar+to+above,+but+between+uppercase+and+lowercase+letters.

//+START+generates+a+log+to+show+us+which+characters+we+are+considering+for+our+UID.
NSMutableString+*chars+=+[NSMutableString+stringWithCapacity:amountOfChars];
for+(int+i+=+charNumStart;+i+<=+charLowerEnd;+i%2B%2B)+{
++++if+((i+>=+charNumStart+&&+i+<=+charNumEnd)+%7C%7C+(i+>=+charCapitalStart+&&+i+<=+charCapitalEnd)+%7C%7C+(i+>=+charLowerStart+&&+i+<=+charLowerEnd))+{
++++++++[chars+appendFormat:@"\n%25c",+(char)+i];
++++}
}
NSLog(@"chars:+%25@",+chars);
//+END+log

//+Generate+a+uid+of+20+characters+that+chooses+from+our+desired+range.
int+uidLength+=+20;
NSMutableString+*uid+=+[NSMutableString+stringWithCapacity:uidLength];
for+(int+i+=+0;+i+<+uidLength;+i%2B%2B)+{
++++//+Generate+a+random+number+within+our+character+range.
++++int+randomNum+=+arc4random()+%25+amountOfChars;
++++//+Add+the+lowest+value+number+to+line+this+up+with+a+desirable+character.
++++randomNum+%2B=+charNumStart;
++++//+if+the+number+is+in+the+letter+range,+skip+over+the+characters+between+the+numbers+and+letters.
++++if+(randomNum+>+charNumEnd)+{
++++++++randomNum+%2B=+firstGap;
++++}
++++//+if+the+number+is+in+the+lowercase+letter+range,+skip+over+the+characters+between+the+uppercase+and+lowercase+letters.
++++if+(randomNum+>+charCapitalEnd)+{
++++++++randomNum+%2B=+secondGap;
++++}
++++//+append+the+chosen+character.
++++[uid+appendFormat:@"%25c",+(char)+randomNum];
}
NSLog(@"uid:+%25@",+uid);

//+Generate+a+UID+that+selects+any+kind+of+character,+including+a+lot+of+punctuation.+It's+a+bit+easier+to+do+it+this+way.
int+amountOfAnyCharacters+=+charLowerEnd+-+charNumStart;+//+A+new+range+of+characters.
NSMutableString+*multiCharUid+=+[NSMutableString+stringWithCapacity:uidLength];
for+(int+i+=+0;+i+<+uidLength;+i%2B%2B)+{
++++//+Generate+a+random+number+within+our+new+character+range.
++++int+randomNum+=+arc4random()+%25+amountOfAnyCharacters;
++++//+Add+the+lowest+value+number+to+line+this+up+with+our+range+of+characters.
++++randomNum+%2B=+charNumStart;
++++//+append+the+chosen+character.
++++[multiCharUid+appendFormat:@"%25c",+(char)+randomNum];
}
NSLog(@"multiCharUid:+%25@",+multiCharUid);|code-block|syntax|javascript|1062763|当我进行随机字符生成时，我更喜欢直接处理整数并对其进行转换，而不是写出我想要从中提取的字符列表。在顶部声明变量使其更加独立于系统，但此代码假设数字的值将低于字母，而大写字母的值将低于小写字母。|1062764|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Here's a different way to tackle it. Instead of using a prepared string of characters, you can cast between integers and characters, and generate a dynamic list of characters to select. It's pretty lean and fast, but has a bit more code. 

<pre><code>int charNumStart = (int) '0';
int charNumEnd = (int) '9';
int charCapitalStart = (int) 'A';
int charCapitalEnd = (int) 'Z';
int charLowerStart = (int) 'a';
int charLowerEnd = (int) 'z';

int amountOfChars = (charNumEnd - charNumStart) + (charCapitalEnd - charCapitalStart) + (charLowerEnd - charLowerStart); // amount of the characters we want.
int firstGap = charCapitalStart - charNumEnd; // there are gaps of random characters between numbers and uppercase letters, so this allows us to skip those.
int secondGap = charLowerStart - charCapitalEnd; // similar to above, but between uppercase and lowercase letters.

// START generates a log to show us which characters we are considering for our UID.
NSMutableString *chars = [NSMutableString stringWithCapacity:amountOfChars];
for (int i = charNumStart; i &lt;= charLowerEnd; i++) {
 if ((i &gt;= charNumStart &amp;&amp; i &lt;= charNumEnd) || (i &gt;= charCapitalStart &amp;&amp; i &lt;= charCapitalEnd) || (i &gt;= charLowerStart &amp;&amp; i &lt;= charLowerEnd)) {
 [chars appendFormat:@"\n%c", (char) i];
 }
}
NSLog(@"chars: %@", chars);
// END log

// Generate a uid of 20 characters that chooses from our desired range.
int uidLength = 20;
NSMutableString *uid = [NSMutableString stringWithCapacity:uidLength];
for (int i = 0; i &lt; uidLength; i++) {
 // Generate a random number within our character range.
 int randomNum = arc4random() % amountOfChars;
 // Add the lowest value number to line this up with a desirable character.
 randomNum += charNumStart;
 // if the number is in the letter range, skip over the characters between the numbers and letters.
 if (randomNum &gt; charNumEnd) {
 randomNum += firstGap;
 }
 // if the number is in the lowercase letter range, skip over the characters between the uppercase and lowercase letters.
 if (randomNum &gt; charCapitalEnd) {
 randomNum += secondGap;
 }
 // append the chosen character.
 [uid appendFormat:@"%c", (char) randomNum];
}
NSLog(@"uid: %@", uid);

// Generate a UID that selects any kind of character, including a lot of punctuation. It's a bit easier to do it this way.
int amountOfAnyCharacters = charLowerEnd - charNumStart; // A new range of characters.
NSMutableString *multiCharUid = [NSMutableString stringWithCapacity:uidLength];
for (int i = 0; i &lt; uidLength; i++) {
 // Generate a random number within our new character range.
 int randomNum = arc4random() % amountOfAnyCharacters;
 // Add the lowest value number to line this up with our range of characters.
 randomNum += charNumStart;
 // append the chosen character.
 [multiCharUid appendFormat:@"%c", (char) randomNum];
}
NSLog(@"multiCharUid: %@", multiCharUid);
</code></pre>

When I'm doing random character generation, I prefer to work directly with integers and cast them over, instead of writing out the list of chars that I want to draw from. Declaring the variables at the top makes it more system independent, but this code assumes that numbers will have a lower value than letters, and that uppercase letters will have a lower value than lowercase letters.

blocks|key|1063251|text|Swift中的替代解决方案|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1063252|func+generateString(len:+Int)+->+String+{
++++let+letters+=+"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
++++let+lettersLength+=+UInt32(countElements(letters))
++++let+result+=+(0..<len).map+{+_+->+String+in
++++++++let+idx+=+Int(arc4random_uniform(lettersLength))
++++++++return+String(letters[advance(letters.startIndex,+idx)])
++++}
++++return+"".join(result)
}|code-block|syntax|javascript|1063253|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|$]]

Alternative solution in Swift

<pre><code>func generateString(len: Int) -&gt; String {
 let letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
 let lettersLength = UInt32(countElements(letters))
 let result = (0..&lt;len).map { _ -&gt; String in
 let idx = Int(arc4random_uniform(lettersLength))
 return String(letters[advance(letters.startIndex, idx)])
 }
 return "".join(result)
}
</code></pre>

blocks|key|1277855|text|生成给定长度的小写字母数字随机字符串：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1277856|-(NSString*)randomStringWithLength:(NSUInteger)length
{
++++NSMutableString*+random+=+[NSMutableString+stringWithCapacity:length];

++++for+(NSUInteger+i=0;+i<length;+i%2B%2B)
++++{
++++++++char+c+=+'0'+%2B+(unichar)arc4random()%2536;
++++++++if(c+>+'9')+c+%2B=+('a'-'9'-1);
++++++++[random+appendFormat:@"%25c",+c];
++++}

++++return+random;
}|code-block|syntax|javascript|1277857|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|$]]

Generates lowercase alphanumeric random string with given length:

<pre><code>-(NSString*)randomStringWithLength:(NSUInteger)length
{
 NSMutableString* random = [NSMutableString stringWithCapacity:length];

 for (NSUInteger i=0; i&lt;length; i++)
 {
 char c = '0' + (unichar)arc4random()%36;
 if(c &gt; '9') c += ('a'-'9'-1);
 [random appendFormat:@"%c", c];
 }

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

blocks|key|1063368|text|在这里和done+Swift+4.0中修改了一些想法|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1063369|extension+String
{
++++subscript+(i:+Int)+->+Character
++++{
++++++++return+self[index(startIndex,+offsetBy:i)]
++++}

++++static+func+Random(length:Int=32,+alphabet:String="ABCDEF0123456789")+->+String
++++{
++++++++let+upperBound+=+UInt32(alphabet.count)
++++++++return+String((0..<length).map+{+_+->+Character+in
++++++++++++return+alphabet[Int(arc4random_uniform(upperBound))]
++++++++})
++++}
}|code-block|syntax|javascript|1063370|用法：|1063371|let+myHexString+=+String.Random()
let+myLongHexString+=+String.Random(length:64)
let+myLettersString+=+String.Random(length:32,+alphabet:"ABCDEFGHIJKLMNOPQRSTUVWXYZ")|1063372|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|$]]

Modification of a few ideas here, and in done Swift 4.0

<pre><code>extension String
{
 subscript (i: Int) -&gt; Character
 {
 return self[index(startIndex, offsetBy:i)]
 }

 static func Random(length:Int=32, alphabet:String="ABCDEF0123456789") -&gt; String
 {
 let upperBound = UInt32(alphabet.count)
 return String((0..&lt;length).map { _ -&gt; Character in
 return alphabet[Int(arc4random_uniform(upperBound))]
 })
 }
}
</code></pre>

Usage:

<pre><code>let myHexString = String.Random()
let myLongHexString = String.Random(length:64)
let myLettersString = String.Random(length:32, alphabet:"ABCDEFGHIJKLMNOPQRSTUVWXYZ")
</code></pre>

blocks|key|1277766|text|如果需要随机unicode字符串，可以创建随机字节，然后使用有效字节。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1277767|++++OSStatus+sanityCheck+=+noErr;
++++uint8_t+*+randomBytes+=+NULL;
++++size_t+length+=+200;+//+can+of+course+be+variable

++++randomBytes+=+malloc(+length+*+sizeof(uint8_t)+);
++++memset((void+*)randomBytes,+0x0,+length);

++++sanityCheck+=+SecRandomCopyBytes(kSecRandomDefault,+length,+randomBytes);

++++if+(sanityCheck+!=+noErr)+NSLog(@"Error+generating+random+bytes,+OSStatus+==+%25ld.",+sanityCheck);

++++NSData*+randomData+=+[[NSData+alloc]+initWithBytes:(const+void+*)randomBytes+length:+length];
++++if+(randomBytes)+free(randomBytes);

++++NSString*+dataString+=+[[NSString+alloc]+initWithCharacters:[randomData+bytes]+length:[randomData+length]];++//+create+an+NSString+from+the+random+bytes
++++NSData*+tempData+=+[dataString+dataUsingEncoding:NSUTF8StringEncoding+allowLossyConversion:YES];+++++++++++++//+remove+illegal+characters+from+string
++++NSString*+randomString+=+[[NSString+alloc]+initWithData:tempData+encoding:NSUTF8StringEncoding];|code-block|syntax|javascript|1277768|要获得有效的NSString+-8字符串，必须进行从UTF到NSData的转换。请注意，长度不一定是最终创建的NSString的长度。|1277769|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

If you want a random unicode string, you can create random bytes and then use the valid ones. 

<pre><code> OSStatus sanityCheck = noErr;
 uint8_t * randomBytes = NULL;
 size_t length = 200; // can of course be variable

 randomBytes = malloc( length * sizeof(uint8_t) );
 memset((void *)randomBytes, 0x0, length);

 sanityCheck = SecRandomCopyBytes(kSecRandomDefault, length, randomBytes);

 if (sanityCheck != noErr) NSLog(@"Error generating random bytes, OSStatus == %ld.", sanityCheck);

 NSData* randomData = [[NSData alloc] initWithBytes:(const void *)randomBytes length: length];
 if (randomBytes) free(randomBytes);

 NSString* dataString = [[NSString alloc] initWithCharacters:[randomData bytes] length:[randomData length]]; // create an NSString from the random bytes
 NSData* tempData = [dataString dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:YES]; // remove illegal characters from string
 NSString* randomString = [[NSString alloc] initWithData:tempData encoding:NSUTF8StringEncoding];
</code></pre>

The conversion from NSString to NSData and back is necessary to get a valid UTF-8 string.
Be aware that length will not necessarily be the length of the the NSString created in the end.

blocks|key|1277803|text|我用一个简单的char[]代替了字母表中的NSString+*。我将其添加到NSString类别中。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1277804|static+const+char+__alphabet[]+=
++++"0123456789"
++++"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
++++"abcdefghijklmnopqrstuvwxyz";
%2B+(NSString+*)randomString:(int)length
{
++++NSMutableString+*randomString+=+[NSMutableString+stringWithCapacity:length];
++++u_int32_t+alphabetLength+=+(u_int32_t)strlen(__alphabet);
++++for+(int+i+=+0;+i+<+length;+i%2B%2B)+{
++++++++[randomString+appendFormat:@"%25c",+__alphabet[arc4random_uniform(alphabetLength)]];
++++}
++++return+randomString;
}|code-block|syntax|javascript|1277805|entityMap^0|7|6|L|A|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

I did this using a simple <code>char[]</code> instead of an <code>NSString *</code> for the alphabet. I added this to a NSString category.

<pre><code>static const char __alphabet[] =
 "0123456789"
 "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 "abcdefghijklmnopqrstuvwxyz";
+ (NSString *)randomString:(int)length
{
 NSMutableString *randomString = [NSMutableString stringWithCapacity:length];
 u_int32_t alphabetLength = (u_int32_t)strlen(__alphabet);
 for (int i = 0; i &lt; length; i++) {
 [randomString appendFormat:@"%c", __alphabet[arc4random_uniform(alphabetLength)]];
 }
 return randomString;
}
</code></pre>

blocks|key|1277813|text|static+NSUInteger+length+=+32;
static+NSString+*letters+=+@"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
NSMutableString+*+randomString+=+[NSMutableString+stringWithCapacity:length];
for+(NSInteger+i+=+0;+i+<+length;+%2B%2Bi)+{
++++[randomString+appendFormat:+@"%25C",+[letters+characterAtIndex:(NSUInteger)arc4random_uniform((u_int32_t)[letters+length])]];
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1277814|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>static NSUInteger length = 32;
static NSString *letters = @"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
NSMutableString * randomString = [NSMutableString stringWithCapacity:length];
for (NSInteger i = 0; i &lt; length; ++i) {
 [randomString appendFormat: @"%C", [letters characterAtIndex:(NSUInteger)arc4random_uniform((u_int32_t)[letters length])]];
}
</code></pre>

blocks|key|1277948|text|#define+ASCII_START_NUMERS+0x30
#define+ASCII_END_NUMERS+0x39
#define+ASCII_START_LETTERS_A+0x41
#define+ASCII_END_LETTERS_Z+0x5A
#define+ASCII_START_LETTERS_a+0x61
#define+ASCII_END_LETTERS_z+0x5A

-(NSString+*)getRandomString:(int)length+{
++++NSMutableString+*result+=+[[NSMutableString+alloc]init];
++++while+(result.length+!=+length)+{
++++++++NSMutableData*+data+=+[NSMutableData+dataWithLength:1];
++++++++SecRandomCopyBytes(kSecRandomDefault,+1,+[data+mutableBytes]);
++++++++Byte+currentChar+=+0;
++++++++[data+getBytes:&currentChar+length:1];
++++++++NSString+*s+=+[[NSString+alloc]+initWithData:data+encoding:NSUTF8StringEncoding];
++++++++if+(currentChar+>+ASCII_START_NUMERS+&&+currentChar+<+ASCII_END_NUMERS)+{+//+0+to+0
++++++++++++[result+appendString:s];
++++++++++++continue;
++++++++}
++++++++if+(currentChar+>+ASCII_START_LETTERS_A+&&+currentChar+<+ASCII_END_LETTERS_Z)+{+//+0+to+0
++++++++++++[result+appendString:s];
++++++++++++continue;
++++++++}
++++++++if+(currentChar+>+ASCII_START_LETTERS_a+&&+currentChar+<+ASCII_END_LETTERS_z)+{+//+0+to+0
++++++++++++[result+appendString:s];
++++++++++++continue;
++++++++}
++++}
++++return+result;
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1277949|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>#define ASCII_START_NUMERS 0x30
#define ASCII_END_NUMERS 0x39
#define ASCII_START_LETTERS_A 0x41
#define ASCII_END_LETTERS_Z 0x5A
#define ASCII_START_LETTERS_a 0x61
#define ASCII_END_LETTERS_z 0x5A

-(NSString *)getRandomString:(int)length {
 NSMutableString *result = [[NSMutableString alloc]init];
 while (result.length != length) {
 NSMutableData* data = [NSMutableData dataWithLength:1];
 SecRandomCopyBytes(kSecRandomDefault, 1, [data mutableBytes]);
 Byte currentChar = 0;
 [data getBytes:&amp;currentChar length:1];
 NSString *s = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
 if (currentChar &gt; ASCII_START_NUMERS &amp;&amp; currentChar &lt; ASCII_END_NUMERS) { // 0 to 0
 [result appendString:s];
 continue;
 }
 if (currentChar &gt; ASCII_START_LETTERS_A &amp;&amp; currentChar &lt; ASCII_END_LETTERS_Z) { // 0 to 0
 [result appendString:s];
 continue;
 }
 if (currentChar &gt; ASCII_START_LETTERS_a &amp;&amp; currentChar &lt; ASCII_END_LETTERS_z) { // 0 to 0
 [result appendString:s];
 continue;
 }
 }
 return result;
}
</code></pre>

blocks|key|1063313|text|修改keithyip的答案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1063314|%2B+(NSString+*)randomAlphanumericStringWithLength:(NSInteger)length
{
++++static+NSString+*+const+letters+=+@"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
++++static+dispatch_once_t+onceToken;
++++dispatch_once(&onceToken,+%5E{
++++++++srand(time(NULL));
++++});

++++NSMutableString+*randomString+=+[NSMutableString+stringWithCapacity:length];

++++for+(int+i+=+0;+i+<+length;+i%2B%2B)+{
++++++++[randomString+appendFormat:@"%25C",+[letters+characterAtIndex:arc4random()+%25+[letters+length]]];
++++}

++++return+randomString;
}|code-block|syntax|javascript|1063315|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|$]]

Modification for keithyip's answer:

<pre><code>+ (NSString *)randomAlphanumericStringWithLength:(NSInteger)length
{
 static NSString * const letters = @"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 static dispatch_once_t onceToken;
 dispatch_once(&amp;onceToken, ^{
 srand(time(NULL));
 });

 NSMutableString *randomString = [NSMutableString stringWithCapacity:length];

 for (int i = 0; i &lt; length; i++) {
 [randomString appendFormat:@"%C", [letters characterAtIndex:arc4random() % [letters length]]];
 }

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

I want to call a method, pass it the length and have it generate a random alphanumeric string.

Are there any utility libraries out there that may have a bunch of these types of functions?

Generate a random alphanumeric string in Cocoa

Swift

我想调用一个方法，将长度传递给它，并让它生成一个随机的字母数字字符串。有没有可能有一堆这样的函数的实用程序库呢？

问在Cocoa中生成随机字母数字字符串
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回答 17

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问在Cocoa中生成随机字母数字字符串
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