16进制NSString与NSData互转

- (NSData*)dataFormHexString:(NSString*)hexString{    hexString=[[string uppercaseString] stringByReplacingOccurrencesOfString:@" " withString:@""];    if (!(hexString && [hexString length] > 0 && [hexString length]%2 == 0)) {        return nil;    }    Byte tempbyt[1]={0};    NSMutableData* bytes=[NSMutableData data];    for(int i=0;i<[hexString length];i++)    {        unichar hex_char1 = [hexString characterAtIndex:i]; ////两位16进制数中的第一位(高位*16)        int int_ch1;        if(hex_char1 >= '0' && hex_char1 <='9')            int_ch1 = (hex_char1-48)*16;   //// 0 的Ascll - 48        else if(hex_char1 >= 'A' && hex_char1 <='F')            int_ch1 = (hex_char1-55)*16; //// A 的Ascll - 65        else            return nil;        i++;                unichar hex_char2 = [hexString characterAtIndex:i]; ///两位16进制数中的第二位(低位)        int int_ch2;        if(hex_char2 >= '0' && hex_char2 <='9')            int_ch2 = (hex_char2-48); //// 0 的Ascll - 48        else if(hex_char2 >= 'A' && hex_char2 <='F')            int_ch2 = hex_char2-55; //// A 的Ascll - 65        else            return nil;                tempbyt[0] = int_ch1+int_ch2;  ///将转化后的数放入Byte数组里        [bytes appendBytes:tempbyt length:1];    }    return bytes;}- (NSString *)hexStringFromData:(NSData*)data{    return [[[[NSString stringWithFormat:@"%@",data]              stringByReplacingOccurrencesOfString: @"<" withString: @""]             stringByReplacingOccurrencesOfString: @">" withString: @""]            stringByReplacingOccurrencesOfString: @" " withString: @""];}