最近在忙一个蓝牙项目,在处理蓝牙数据的时候,经常遇到进制之间的转换,蓝牙处理的是16进制(NSData),而我们习惯的计数方式是10进制,为了节省空间,蓝牙也会把16进制(NSData)拆成2进制记录。这里我们研究下如何在他们之间进行转换。
假设我们要向蓝牙发送0x1B9901这条数据
Byte转NSData
Byte value[3]={ 0};value[0]=0x1B; value[1]=0x99; value[2]=0x01; NSData * data = [NSData dataWithBytes:&value length:sizeof(value)]; //发送数据 [self.peripheral writeValue:data forCharacteristic:self.write type:CBCharacteristicWriteWithoutResponse];
- 优点:这种方法比较简单,没有进行转换,直接一个字节一个字节的拼装好发送出去。
- 缺点:当发送数据比较长时会很麻烦,而且不易更改。
NSString转NSData
- (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; } //发送数据 [self.peripheral writeValue:[self hexToBytes:@"1B9901"] forCharacteristic:self.write type:CBCharacteristicWriteWithoutResponse];
- 优点:比较直观,可以一次转换一长条数据,对于一些功能简单的蓝牙程序,这种转换能处理大部分情况。
- 缺点:只能发送一些固定的指令,不能参与计算。
求校验和
接下来探讨下发送的数据需要计算的情况。
最常用的发送数据需要计算的场景是求校验和(CHECKSUM)。这个根据硬件厂商来定,常见的求校验和的规则有:- 如果发送数据长度为n字节,则CHECKSUM为前n-1字节之和的低字节
- CHECKSUM=0x100-CHECKSUM(上一步的校验和)
如果我要发送带上校验和的0x1B9901,方法就是:
- (NSData *)getCheckSum:(NSString *)byteStr{int length = (int)byteStr.length/2;NSData *data = [self hexToBytes:byteStr];Byte *bytes = (unsigned char *)[data bytes]; Byte sum = 0; for (int i = 0; i[self.peripheral writeValue:data forCharacteristic:self.write type:CBCharacteristicWriteWithoutResponse];
拆分数据
这种是比较麻烦的,举个栗子:在传输某条信息时,我想把时间放进去,不能用时间戳,还要节省空间,这样就出现了一种新的方式存储时间。
这里再补充一些C语言知识:- 一个字节8位(bit)
- char 1字节 int 4字节 unsigned 2字节 float 4字节
存储时间的条件是:
- 只用四个字节(32位)
- 前5位表示年(从2000年算起),接着4位表示月,接着5位表示日,接着5位表示时,接着6位表示分,接着3位表示星期,剩余4位保留。
这样直观的解决办法就是分别取出现在时间的年月日时分星期,先转成2进制,再转成16进制发出去。当然你这么写进去,读的时候就要把16进制数据先转成2进制再转成10进制显示。我们就按这个简单粗暴的思路来,准备工作如下:
10进制转2进制
// 十进制转二进制- (NSString *)toBinarySystemWithDecimalSystem:(int)num length:(int)length{int remainder = 0; //余数 int divisor = 0; //除数 NSString * prepare = @""; while (true) { remainder = num%2; divisor = num/2; num = divisor; prepare = [prepare stringByAppendingFormat:@"%d",remainder]; if (divisor == 0) { break; } } //倒序输出 NSString * result = @""; for (int i = length -1; i >= 0; i --) { if (i <= prepare.length - 1) { result = [result stringByAppendingFormat:@"%@", [prepare substringWithRange:NSMakeRange(i , 1)]]; }else{ result = [result stringByAppendingString:@"0"]; } } return result; }
2进制转10进制
// 二进制转十进制- (NSString *)toDecimalWithBinary:(NSString *)binary{int ll = 0 ;int temp = 0 ; for (int i = 0; i < binary.length; i ++) { temp = [[binary substringWithRange:NSMakeRange(i, 1)] intValue]; temp = temp * powf(2, binary.length - i - 1); ll += temp; } NSString * result = [NSString stringWithFormat:@"%d",ll]; return result; }
16进制和2进制互转
- (NSString *)getBinaryByhex:(NSString *)hex binary:(NSString *)binary{NSMutableDictionary *hexDic = [[NSMutableDictionary alloc] init];hexDic = [[NSMutableDictionary alloc] initWithCapacity:16];[hexDic setObject:@"0000" forKey:@"0"]; [hexDic setObject:@"0001" forKey:@"1"]; [hexDic setObject:@"0010" forKey:@"2"]; [hexDic setObject:@"0011" forKey:@"3"]; [hexDic setObject:@"0100" forKey:@"4"]; [hexDic setObject:@"0101" forKey:@"5"]; [hexDic setObject:@"0110" forKey:@"6"]; [hexDic setObject:@"0111" forKey:@"7"]; [hexDic setObject:@"1000" forKey:@"8"]; [hexDic setObject:@"1001" forKey:@"9"]; [hexDic setObject:@"1010" forKey:@"a"]; [hexDic setObject:@"1011" forKey:@"b"]; [hexDic setObject:@"1100" forKey:@"c"]; [hexDic setObject:@"1101" forKey:@"d"]; [hexDic setObject:@"1110" forKey:@"e"]; [hexDic setObject:@"1111" forKey:@"f"]; NSMutableString *binaryString=[[NSMutableString alloc] init]; if (hex.length) { for (int i=0; i<[hex length]; i++) { NSRange rage; rage.length = 1; rage.location = i; NSString *key = [hex substringWithRange:rage]; [binaryString appendString:hexDic[key]]; } }else{ for (int i=0; i
有了这几种转换函数,完成上面的功能就容易多了,具体怎么操作这里就不写一一出来了。但总感觉怪怪的,这么一个小功能怎么要写这么一大堆代码,当然还可以用C语言的方法去解决。这里主要是为了展示iOS中数据如何转换,C语言的实现方法这里就不写了,有兴趣的同学可以研究下。
附带两个函数
int转NSData
- (NSData *) setId:(int)Id {//用4个字节接收Byte bytes[4];bytes[0] = (Byte)(Id>>24); bytes[1] = (Byte)(Id>>16); bytes[2] = (Byte)(Id>>8); bytes[3] = (Byte)(Id); NSData *data = [NSData dataWithBytes:bytes length:4]; }
NSData转int
接受到的数据0x00000a0122
//4字节表示的intNSData *intData = [data subdataWithRange:NSMakeRange(2, 4)]; int value = CFSwapInt32BigToHost(*(int*)([intData bytes]));//655650 //2字节表示的int NSData *intData = [data subdataWithRange:NSMakeRange(4, 2)]; int value = CFSwapInt16BigToHost(*(int*)([intData bytes]));//290 //1字节表示的int char *bs = (unsigned char *)[[data subdataWithRange:NSMakeRange(5, 1) ] bytes]; int value = *bs;//34
这两个转换在某些场景下使用频率也是挺高的,蓝牙里面的数据转换基本也就这么多了,希望能够帮助大家。
更多关于字节编码的问题,大家可以点这里:
1. NSString转化为UNICODE String:
(NSString*)fname = @“Test”;
char fnameStr[10];
memcpy(fnameStr, [fname cStringUsingEncoding:NSUnicodeStringEncoding], 2*([fname length]));
(NSString*)fname = @“Test”;
char fnameStr[10];
fnameStr =[fname UTF8String];
3. char -> NSData:
方法一:
char * postData = "TEST";
NSData *data = [NSData dataWithBytes:postData length:strlen(postData)];
方法二:
转换为NSString: - (id)initWithUTF8String:(const char *)bytes
然后用NSString的 - (NSData *)dataUsingEncoding:(NSStringEncoding)encoding4. NSData ->char
NSData returnData ;
char* bu=[returnData bytes];
5. NSData->NSString
NSString* aStr;
aStr = [[NSString alloc] initWithData:aData encoding:NSASCIIStringEncoding];
6. NSString->NSData
NSData* aData;
aData = [aStr dataUsingEncoding: NSASCIIStringEncoding];
1. NSData 与 NSString
NSData-> NSString
NSString *aString = [[NSString alloc] initWithData:adataencoding:NSUTF8StringEncoding];
NSString->NSData
NSString *aString = @"1234abcd";
NSData *aData = [aString dataUsingEncoding: NSUTF8StringEncoding];
2.NSData 与 Byte
NSData-> Byte数组
NSString *testString = @"1234567890";
NSData *testData = [testString dataUsingEncoding: NSUTF8StringEncoding];
Byte *testByte = (Byte *)[testData bytes];
for(int i=0;i<[testData length];i++)
printf("testByte = %d\n",testByte[i]);
Byte数组-> NSData
Byte byte[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23};
NSData *adata = [[NSData alloc] initWithBytes:byte length:24];
Byte数组->16进制数
Byte *bytes = (Byte *)[aData bytes];
NSString *hexStr=@"";
for(int i=0;i<[encryData 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(@"bytes 的16进制数为:%@",hexStr);
16进制数->Byte数组
/ 将16进制数据转化成Byte 数组
NSString *hexString = @"3e435fab9c34891f"; //16进制字符串
int j=0;
Byte bytes[128]; ///3ds key的Byte 数组, 128位
for(int i=0;i<[hexString length];i++)
{
int int_ch; /// 两位16进制数转化后的10进制数
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
int_ch1 = (hex_char1-87)*16; a 的Ascll - 97
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_char1 >= 'A' && hex_char1 <='F')
int_ch2 = hex_char2-55; A 的Ascll - 65
else
int_ch2 = hex_char2-87; a 的Ascll - 97
int_ch = int_ch1+int_ch2;
NSLog(@"int_ch=%d",int_ch);
bytes[j] = int_ch; ///将转化后的数放入Byte数组里
j++;
}
NSData *newData = [[NSData alloc] initWithBytes:bytes length:128];
NSLog(@"newData=%@",newData);
3. NSData 与 UIImage
NSData->UIImage
UIImage *aimage = [UIImage imageWithData: imageData];
//例:从本地文件沙盒中取图片并转换为NSData
NSString *path = [[NSBundle mainBundle] bundlePath];
NSString *name = [NSString stringWithFormat:@"ceshi.png"];
NSString *finalPath = [path stringByAppendingPathComponent:name];
NSData *imageData = [NSData dataWithContentsOfFile: finalPath];
UIImage *aimage = [UIImage imageWithData: imageData];
UIImage-> NSData
NSData *imageData = UIImagePNGRepresentation(aimae);
把16进制字符串转换成NSData:
- -(NSData *)hexString:(NSString *)hexString {
- int j=0;
- Byte bytes[20];
- ///3ds key的Byte 数组, 128位
- for(int i=0; i<[hexString length]; i++)
- {
- int int_ch; /// 两位16进制数转化后的10进制数
- 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
- int_ch1 = (hex_char1-87)*16; a 的Ascll - 97
- 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_char1 >= 'A' && hex_char1 <='F')
- int_ch2 = hex_char2-55; A 的Ascll - 65
- else
- int_ch2 = hex_char2-87; a 的Ascll - 97
- int_ch = int_ch1+int_ch2;
- NSLog(@"int_ch=%d",int_ch);
- bytes[j] = int_ch; ///将转化后的数放入Byte数组里
- j++;
- }
- NSData *newData = [[NSData alloc] initWithBytes:bytes length:20];
- return newData;
- }
扩展
基于CoreBluetooth4.0框架的连接BLE4.0的Demo: