iOS NSData 轉 字符串 （藍牙特徵值轉字符串）

該方法用於在接收到藍牙設備傳送過來的特徵值（NSData）數據後，轉化爲字符串類型，方便取用

- (NSString *)transformCharateristicValueFromData:(NSData *)dataValue{
    if (!dataValue || [dataValue length] == 0) {
        return @"";
    }
    NSMutableString *destStr = [[NSMutableString alloc]initWithCapacity:[dataValue length]];
    
    [dataValue enumerateByteRangesUsingBlock:^(const void * _Nonnull bytes, NSRange byteRange, BOOL * _Nonnull stop) {
        unsigned char *dataBytes = (unsigned char *)bytes;
        for (int i = 0; i < byteRange.length; i++) {
            NSString *hexStr = [NSString stringWithFormat:@"%x",(dataBytes[i]) & 0xff];
            if ([hexStr length] == 2) {
                [destStr appendString:hexStr];
            }else{
                [destStr appendFormat:@"0%@",hexStr];
            }
        }
    }];
    return destStr;
}