类似UUID的随机字符

.h

+(NSString *)getUUID;

---

.m

//当前时间（毫秒级）+随机数和打乱的字符串 进行洗牌（洗牌算法）

+(NSString *)getUUID{

NSString* date;

NSDateFormatter * formatter = [[NSDateFormatter alloc ] init];

[formatter setDateFormat:@"YYYYMMddhhmmssSSS"];

date = [formatter stringFromDate:[NSDate date]];

NSString *  timeNow = [[NSString alloc] initWithFormat:@"%@", date];

int x = (arc4random() % 1001) + 8999;

NSString *alphabet = @"ABCDEFGHIJK";

// Get the characters into a C array for efficient shuffling

NSUInteger numberOfCharacters = [alphabet length];

unichar *characters = calloc(numberOfCharacters, sizeof(unichar));

[alphabet getCharacters:characters range:NSMakeRange(0, numberOfCharacters)];

// Perform a Fisher-Yates shuffle

for (NSUInteger i = 0; i < numberOfCharacters; ++i) {

NSUInteger j = (arc4random_uniform(numberOfCharacters - i) + i);

unichar c = characters[i];

characters[i] = characters[j];

characters[j] = c;

}

NSString *result = [NSString stringWithCharacters:characters length:numberOfCharacters];

free(characters);

NSString *UDID = [NSString stringWithFormat:@"%@%d%@",timeNow,x,result];

NSString *alphabet1 = UDID;

// Get the characters into a C array for efficient shuffling

NSUInteger numberOfCharacters1 = [alphabet1 length];

unichar *characters1 = calloc(numberOfCharacters1, sizeof(unichar));

[alphabet1 getCharacters:characters1 range:NSMakeRange(0, numberOfCharacters1)];

// Perform a Fisher-Yates shuffle

for (NSUInteger i = 0; i < numberOfCharacters1; ++i) {

NSUInteger j = (arc4random_uniform(numberOfCharacters1 - i) + i);

unichar c = characters1[i];

characters1[i] = characters1[j];

characters1[j] = c;

}

NSString *UUID = [NSString stringWithCharacters:characters1 length:numberOfCharacters1];

free(characters1);

NSMutableString *uuid2 = [[NSMutableString alloc] initWithString:UUID];

[uuid2 insertString:@"-" atIndex:8];

[uuid2 insertString:@"-" atIndex:13];

[uuid2 insertString:@"-" atIndex:18];

[uuid2 insertString:@"-" atIndex:23];

return uuid2;

}

//这个想法不是很严谨，不能完全的保证唯一性。

//在数据量不是特别大或者特定情况下可以当做唯一标示符使用。