IOS蓝牙开发之------------校验和计算

上一篇已经介绍过蓝牙连接的具体步骤,其中重要的就是数据的写入和读取,数据的写入需要根据<蓝牙协议>(这个协议硬件开发的会给)的规则来写入.
其中这里面有个需要计算的就是checkSUM(校验和).不懂什么是校验和的可以自行百度下,这里就不多赘述了直接上代码了.

//求累加和(校验和)(CHECKSUM)的求法
- (NSData *)getCheckSum:(NSData *)byteStr{
    int length = (int)byteStr.length;
    // NSData *data = [self hexToBytes:byteStr];
    Byte *bytes = (unsigned char *)[byteStr bytes];
    Byte sum = 0;
    for (int i = 0; i<length; i++) {
        sum += bytes[i];
    }
    int sumT = sum;
    int at = 256 -  sumT;
    
    printf("校验和：%d\n",at);
    printf("累加和：%d\n",sumT);
    if (at == 256) {
        at = 0;
    }
    NSString *str = [NSString stringWithFormat:@"%@",[self ToHex:sumT]];
    return [self hexToBytes:str];
}
//将十进制转化为十六进制
- (NSString *)ToHex:(int)tmpid
{
    NSString *nLetterValue;
    NSString *str =@"";
    int ttmpig;
    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 stringWithFormat:@"%u",ttmpig];
                
        }
        str = [nLetterValue stringByAppendingString:str];
        if (tmpid == 0) {
            break;
        }
    }
    //NSLog(@"16进制是：%@",str);
    //不够一个字节凑0
    if(str.length == 1){
        return [NSString stringWithFormat:@"0%@",str];
    }else{
        return str;
    }
}
- (NSData *)hexToBytes:(NSString *)str
{
    NSMutableData* data = [NSMutableData data];
    int idx;
    for (idx = 0; idx+2 <= str.length; idx+=2) {
        NSRange range = NSMakeRange(idx, 2);
        NSString* hexStr = [str substringWithRange:range];
        NSScanner* scanner = [NSScanner scannerWithString:hexStr];
        unsigned int intValue;
        [scanner scanHexInt:&intValue];
        [data appendBytes:&intValue length:1];
    }
    
    return data;
}
//字符串转为NSData（非编码）：
- (NSData *)convertHexStrToData:(NSString *)str {
    if (!str || [str length] == 0) {
        return nil;
    }
    
    NSMutableData *hexData = [[NSMutableData alloc] initWithCapacity:8];
    NSRange range;
    if ([str length] % 2 == 0) {
        range = NSMakeRange(0, 2);
    } else {
        range = NSMakeRange(0, 1);
    }
    for (NSInteger i = range.location; i < [str length]; i += 2) {
        unsigned int anInt;
        NSString *hexCharStr = [str substringWithRange:range];
        NSScanner *scanner = [[NSScanner alloc] initWithString:hexCharStr];
        
        [scanner scanHexInt:&anInt];
        NSData *entity = [[NSData alloc] initWithBytes:&anInt length:1];
        [hexData appendData:entity];
        
        range.location += range.length;
        range.length = 2;
    }
    
    // NSLog(@"hexdata: %@", hexData);
    return hexData;
}