如何在SQLITE中生成唯一的GUID 36字符iPhone

Question

我正在嘗試創建一個唯一且具有主鍵的表。我知道在sqlite中，我們可以開發唯一的AUTOINCREMENT ID SQL AUTOINCREMENT，但可以生成長度爲36個字符的唯一GUID。這樣做的唯一理由是讓它更獨特。

Answer 1

這是代碼位我使用的UUID（我甚至可能已經發現，在這裏對堆棧溢出）...

+ (NSString *)GetUUID 
{ 
    CFUUIDRef theUUID = CFUUIDCreate(NULL); 
    CFStringRef string = CFUUIDCreateString(NULL, theUUID); 
    CFRelease(theUUID); 
    return [(NSString *)string autorelease]; 
} 

不知所產生的UUID有多長因爲在我使用它的方式中，我不在乎，所以可以通過將結果傳遞給NSLog調用來檢查。

HTH，Pedro :)

Answer 2

我使用這段代碼來生成iphone上的GUID - NSString上的類別。不記得我在哪裏找到它，但它效果很好。

#import "NSString_UniqueID.h" 


static unichar x (unsigned int); 

@implementation NSString (TWUUID) 

+ (NSString*) stringWithUniqueId 
{ 
    CFUUIDRef uuid = CFUUIDCreate(NULL); 
    CFUUIDBytes b = CFUUIDGetUUIDBytes(uuid); 
    unichar unichars[22]; 
    unichar* c = unichars; 
    *c++ = x(b.byte0 >> 2); 
    *c++ = x((b.byte0 & 3 << 4) + (b.byte1 >> 4)); 
    *c++ = x((b.byte1 & 15 << 2) + (b.byte2 >> 6)); 
    *c++ = x(b.byte2 & 63); 
    *c++ = x(b.byte3 >> 2); 
    *c++ = x((b.byte3 & 3 << 4) + (b.byte4 >> 4)); 
    *c++ = x((b.byte4 & 15 << 2) + (b.byte5 >> 6)); 
    *c++ = x(b.byte5 & 63); 
    *c++ = x(b.byte6 >> 2); 
    *c++ = x((b.byte6 & 3 << 4) + (b.byte7 >> 4)); 
    *c++ = x((b.byte7 & 15 << 2) + (b.byte8 >> 6)); 
    *c++ = x(b.byte8 & 63); 
    *c++ = x(b.byte9 >> 2); 
    *c++ = x((b.byte9 & 3 << 4) + (b.byte10 >> 4)); 
    *c++ = x((b.byte10 & 15 << 2) + (b.byte11 >> 6)); 
    *c++ = x(b.byte11 & 63); 
    *c++ = x(b.byte12 >> 2); 
    *c++ = x((b.byte12 & 3 << 4) + (b.byte13 >> 4)); 
    *c++ = x((b.byte13 & 15 << 2) + (b.byte14 >> 6)); 
    *c++ = x(b.byte14 & 63); 
    *c++ = x(b.byte15 >> 2); 
    *c = x(b.byte15 & 3); 
    CFRelease(uuid); 
    return [NSString stringWithCharacters: unichars length: 22]; 
} 
@end 
// Convert six-bit values into letters, numbers or _ or $ (64 characters in that set). 
//------------------------------------------------------------------------------------ 
unichar x (unsigned int c) 
{ 
    if (c < 26) return 'a' + c; 
    if (c < 52) return 'A' + c - 26; 
    if (c < 62) return '0' + c - 52; 
    if (c == 62) return '$'; 
    return '_'; 
}