1.NSData与NSString常规转换

NSData *data =[str dataUsingEncoding:NSUTF8StringEncoding];
NSString * str  =[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

2.NSData 转成十六进制格式NSString

例如：NSData实例转换成字符串形式输出0000b5be

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

3.十六进制格式NSString 转NSData

与上面2刚好相反

-(NSData*) convertBytesStringToData {
    NSMutableData* data = [NSMutableData data];
    int idx;
    for (idx = 0; idx+2 <= self.length; idx+=2) {
        NSRange range = NSMakeRange(idx, 2);
        NSString* hexStr = [self substringWithRange:range];
        NSScanner* scanner = [NSScanner scannerWithString:hexStr];
        unsigned int intValue;
        [scanner scanHexInt:&intValue];
        [data appendBytes:&intValue length:1];
    }
    return data;
}

4.十进制格式字符转十六进制格式字符

- (NSString *)decimalToHex {
    long long int tmpid = [self intValue];
    NSString *nLetterValue;
    NSString *str = @"";
    long long 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 alloc]initWithFormat:@"%lli", ttmpig];
        }
        str = [nLetterValue stringByAppendingString:str];
        if (tmpid == 0) {
            break;
        }
    }
    return str;
}

5.十六进制字符转十进制字符

- (NSString *)hexToDecimal {
    return [NSString stringWithFormat:@"%lu",strtoul([self UTF8String],0,16)];
}