近期做了蓝牙通信这一块，中间遇到了许多数据之间的进制转换、数据类型的转换，在这里记录一下，也给大家分享一下。
我自己建了一个NSString的类别（Category），把这些方法放进去，用的时候就方便多了。

16进制字符串转换成NSData数据类型

#pragma mark - 16进制字符串转data
+ (NSData *)stringToHexData:(NSString *)hexStr
{
    unsigned long len = [hexStr length] / 2;    // Target length
    unsigned char *buf = malloc(len);
    unsigned char *whole_byte = buf;
    char byte_chars[3] = {'\0','\0','\0'};
    
    int i;
    for (i=0; i < [hexStr length] / 2; i++) {
        byte_chars[0] = [hexStr characterAtIndex:i*2];
        byte_chars[1] = [hexStr characterAtIndex:i*2+1];
        *whole_byte = strtol(byte_chars, NULL, 16);
        whole_byte++;
    }
    NSData *data = [NSData dataWithBytes:buf length:len];
    free( buf );
    return data;
}

NSData数据类型转换成16进制字符串

#pragma mark - data转换为十六进制的string
+ (NSString *)hexStringFromData:(NSData *)myData{
    
    Byte *bytes = (Byte *)[myData bytes];
    //下面是Byte 转换为16进制。
    NSString *hexStr=@"";
    for(int i=0;i<[myData length];i++)
        
    {
        NSString *newHexStr = [NSString stringWithFormat:@"%x",bytes[i]&0xff];///16进制数
        
        if([newHexStr length]==1)
            
            hexStr = [NSString stringWithFormat:@"%@0%@",hexStr,newHexStr];
        
        else
            
            hexStr = [NSString stringWithFormat:@"%@%@",hexStr,newHexStr];
    }
    NSLog(@"hex = %@",hexStr);
    
    return hexStr;
}

16进制字符串转换成NSData后按位异或

#pragma mark - 16进制字符串转换成data后按位异或
+ (NSString*)xorWithHexString:(NSString*)hexString range:(NSRange)range {
    if (!hexString || (range.length == 0) ) {
        return nil;
    }
    NSData *hexData = [NSString stringToHexData:[hexString substringWithRange:range]];
    NSLog(@"hexData = %@",hexData);
    Byte *byte = (Byte*)hexData.bytes;
    for (int i=0; i<hexData.length - 1; i++) {
        byte[0] ^= byte[i + 1];
    }
    NSLog(@"byte[0] = %02x",byte[0]);
    NSData *resultData = [NSData dataWithBytes:byte length:1];
    return [NSString hexStringFromData:resultData];
}

例如：10 01 00 04 31 32 33 34， 最后按位异或的结果是：11

10进制字符串转换成16进制字符串

#pragma mark - 10进制转16进制
+ (NSString *)hexStringFromDecString:(NSString*)decString
{
    NSString *nLetterValue;
    NSString *str =@"";
    long long int ttmpig;
    long long int tmpid = [decString longLongValue];
    for (int i =0; i<9; i++) {
        ttmpig=tmpid%16;
        tmpid=tmpid/16;
        switch (ttmpig)
        {
            case 10:
                nLetterValue =@"A";break;
            case 11:
                nLetterValue =@"B";break;
            case 12:
                nLetterValue =@"C";break;
            case 13:
                nLetterValue =@"D";break;
            case 14:
                nLetterValue =@"E";break;
            case 15:
                nLetterValue =@"F";break;
            default:nLetterValue=[[NSString alloc]initWithFormat:@"%lli",ttmpig];
                
        }
        str = [nLetterValue stringByAppendingString:str];
        if (tmpid == 0) {
            break;
        }
    }
    NSLog(@"str = %@",str);
    return str;
}

16进制字符串转换成2进制字符串

#pragma mark - 16进制字符串转2进制字符串
+ (NSString*)binStringFromHexString:(NSString*)hexStr {
    NSMutableArray *arr = [NSMutableArray arrayWithCapacity:0];
    for (int i=0;i<hexStr.length;i++) {
        NSString* str = [hexStr substringWithRange:NSMakeRange(i, 1)];
        [arr addObject:[self binString:str]];;
    }
    NSString *binStr = [arr componentsJoinedByString:@""];
    NSLog(@"binStr = %@",binStr);
    return binStr;
}
+ (NSString*)binString:(NSString*)str {
    if ([str isEqualToString:@"0"]) {
        return @"0000";
    } else if ([str isEqualToString:@"1"]) {
        return @"0001";
    } else if ([str isEqualToString:@"2"]) {
        return @"0010";
    } else if ([str isEqualToString:@"3"]) {
        return @"0011";
    } else if ([str isEqualToString:@"4"]) {
        return @"0100";
    } else if ([str isEqualToString:@"5"]) {
        return @"0101";
    } else if ([str isEqualToString:@"6"]) {
        return @"0110";
    } else if ([str isEqualToString:@"7"]) {
        return @"0111";
    } else if ([str isEqualToString:@"8"]) {
        return @"1000";
    } else if ([str isEqualToString:@"9"]) {
        return @"1001";
    } else if ([str isEqualToString:@"a"]) {
        return @"1010";
    } else if ([str isEqualToString:@"b"]) {
        return @"1011";
    } else if ([str isEqualToString:@"c"]) {
        return @"1100";
    } else if ([str isEqualToString:@"d"]) {
        return @"1101";
    } else if ([str isEqualToString:@"e"]) {
        return @"1110";
    } else if ([str isEqualToString:@"f"]) {
        return @"1111";
    } else {
        return nil;
    }
}

这些有些是自己写的，有些是从网上找到的，亲测有效。