使用socket发送数据的时候，有时要求发送Byte数组，在网关(Lora)、蓝牙外设等硬件传输的时候常常用到。
安卓端处理起来较容易，iOS因为语言的问题，处理起来没有那么友好。
我项目中用到的是与Lora网关传输的数据转换代码，基本上所有的数据转换情况都包含了。

@implementation NSString (Hex)

///NSData转16进制
+(NSString *)hexStringFromData:(NSData *)data{
    if (data.length<=0) {
        return @"";
    }
    NSMutableString *hexString = [[NSMutableString alloc] init];
    const Byte *bytes = data.bytes;
    for (NSUInteger i=0; i<data.length; i++) {
        Byte value = bytes[i];
        Byte high = (value & 0xf0) >> 4;
        Byte low = value & 0xf;
        [hexString appendFormat:@"%x%x", high, low];
    }//for
    return hexString;
}

/// 16进制转NSData
+(NSData *)dataFromHexString:(NSString *)hexString{
    if (hexString.length == 0 ||
        hexString.length % 2) {
        return [NSData data];
    }
    NSMutableData *data = [[NSMutableData alloc] init];
    for (NSUInteger i=0; i<hexString.length; i+=2) {
        NSRange tempRange = NSMakeRange(i, 2);
        NSString *tempStr = [hexString substringWithRange:tempRange];
        NSScanner *scanner = [NSScanner scannerWithString:tempStr];
        unsigned int tempIntValue;
        [scanner scanHexInt:&tempIntValue];
        [data appendBytes:&tempIntValue length:1];
    }
    return data;
}

//int 转16进制
+ (NSString *)hexFromInt:(NSInteger)val {
    return [NSString stringWithFormat:@"%X", val];
}

/// NSString 转NSData
+(NSData*)dataFromString:(NSString *)aString{
    // 通过utf-8转为data
    NSData* data = [aString dataUsingEncoding:NSUTF8StringEncoding];
    return data;
}

/// uint8转NSData(占两位)
+(NSData *)byteFromUInt8:(uint8_t)val{
    NSMutableData *valData = [[NSMutableData alloc] init];
    unsigned char valChar[1];
    valChar[0] = 0xff & val;
    [valData appendBytes:valChar length:1];
    return [self dataWithReverse:valData];
}

///uint16转NSData(占四位)
///prioryHight: YES（转化的Data为高位在前），NO（转化的Data为低位在前）
+(NSData *)byteFromUInt16:(uint16_t)val prioryHight:(BOOL)prioryHight{
    NSMutableData *valData = [[NSMutableData alloc] init];
        
    unsigned char valChar[2];
    valChar[0] = 0xff & val;
    valChar[1] = (0xff00 & val) >> 8;
    [valData appendBytes:valChar length:2];
    
    NSData* resultData = valData;
    if (prioryHight) {
        resultData = [self dataWithReverse:valData];
    }
    
    return resultData;
}

/// uint32转NSData(占八位)
/// prioryHight: YES（转化的Data为高位在前），NO（转化的Data为低位在前）
+(NSData *)byteFromUInt32:(uint32_t)val prioryHight:(BOOL)prioryHight{
    NSMutableData *valData = [[NSMutableData alloc] init];
    unsigned char valChar[4];
    valChar[0] = 0xff & val;
    valChar[1] = (0xff00 & val) >> 8;
    valChar[2] = (0xff0000 & val) >> 16;
    valChar[3] = (0xff000000 & val) >> 24;
    [valData appendBytes:valChar length:4];
    NSData* resultData = valData;
    if (prioryHight) {
        resultData = [self dataWithReverse:valData];
    }
    return resultData;
}

/// NSData转Uint8
+(uint8_t)uint8FromBytes:(NSData *)fData{
    if (fData.length!=1) {
        NSLog(@"uint8FromBytes: (data length != 1)");
        return 0;
    }
    NSData *data = fData;
    uint8_t val = 0;
    [data getBytes:&val length:1];
    return val;
}

/// NSData转Uint16
+(uint16_t)uint16FromBytes:(NSData *)fData prioryHight:(BOOL)prioryHight{
    if (fData.length!=2) {
        NSLog(@"uint16FromBytes: (data length != 2)");
        return 0;
    }
    NSData *data = fData;
    if (prioryHight) {
        [self dataWithReverse:fData];
    }
    uint16_t val0 = 0;
    uint16_t val1 = 0;
    [data getBytes:&val0 range:NSMakeRange(0, 1)];
    [data getBytes:&val1 range:NSMakeRange(1, 1)];
    
    uint16_t dstVal = (val0 & 0xff) + ((val1 << 8) & 0xff00);
    
    return dstVal;
}

/// NSData转Uint32
+(uint32_t)uint32FromBytes:(NSData *)fData prioryHight:(BOOL)prioryHight{
    if (fData.length!=4) {
        NSLog(@"uint32FromBytes: (data length != 4)");
        return 0;
    }
    NSData *data = fData;
    if (prioryHight) {
        [self dataWithReverse:fData];
    }
    
    uint32_t val0 = 0;
    uint32_t val1 = 0;
    uint32_t val2 = 0;
    uint32_t val3 = 0;
    [data getBytes:&val0 range:NSMakeRange(0, 1)];
    [data getBytes:&val1 range:NSMakeRange(1, 1)];
    [data getBytes:&val2 range:NSMakeRange(2, 1)];
    [data getBytes:&val3 range:NSMakeRange(3, 1)];
    
    uint32_t dstVal = (val0 & 0xff) + ((val1 << 8) & 0xff00) + ((val2 << 16) & 0xff0000) + ((val3 << 24) & 0xff000000);
    return dstVal;
}

///NSData转int
+(int)intFromData:(NSData*)fData{
    if (fData.length == 4) {
        NSLog(@"uint32FromBytes: (data length != 4)");
        return 0;
    }
    int result = CFSwapInt32BigToHost(*(int*)([fData bytes]));
    return result;
}

/// 反转字节序列代码
+(NSData *)dataWithReverse:(NSData *)srcData{
    NSUInteger byteCount = srcData.length;
    NSMutableData *dstData = [[NSMutableData alloc] initWithData:srcData];
    NSUInteger halfLength = byteCount / 2;
    for (NSUInteger i=0; i<halfLength; i++) {
        NSRange begin = NSMakeRange(i, 1);
        NSRange end = NSMakeRange(byteCount - i - 1, 1);
        NSData *beginData = [srcData subdataWithRange:begin];
        NSData *endData = [srcData subdataWithRange:end];
        [dstData replaceBytesInRange:begin withBytes:endData.bytes];
        [dstData replaceBytesInRange:end withBytes:beginData.bytes];
    }//for
    
    return dstData;
}

/// 检验和
+(NSString*)hexCheckSumFromString:(NSString *)aString{
    if (aString.length==0) {
        return @"";
    }
    
    int iTotal = 0;
    int iLen = (int)aString.length;
    int iNum = 0;
    
    while (iNum < iLen) {
        NSString* byteString = [aString substringWithRange:NSMakeRange(iNum, 2)];
        iTotal += strtoul([byteString UTF8String], 0, 16);
        iNum = iNum + 2;
    }
    //用256求余最大是255，即16进制的FF
    
    int iMod = iTotal % 256;
    //int转16进制串
    NSString* sHex = [NSString stringWithFormat:@"%x",iMod];

    //如果不够校验位的长度，补0，这里用的是两位校验
    if (sHex.length<2) {
        sHex = [NSString stringWithFormat:@"0%@",sHex];
    }
    return sHex;
}

/// 字符串转ascii字符串
+(NSString*)asciStringFromString:(NSString *)aString{
    NSMutableString* muString = [[NSMutableString alloc] init];
    const char *ch = [aString cStringUsingEncoding:NSASCIIStringEncoding];
    for (int i=0; i<strlen(ch); i++) {
        [muString appendString:[NSString stringWithFormat:@"%x",ch[i]]];
    }
    return muString;
}
@end