IOS Core蓝牙:为特性编写NSData

Question

我使用以下代码使用IOS Core蓝牙为蓝牙特性(重置设备)写入0xDE值:

...
NSData *bytes = [@"0xDE" dataUsingEncoding:NSUTF8StringEncoding];
[peripheral writeValue:bytes
            forCharacteristic:characteristic
            type:CBCharacteristicWriteWithResponse];
...

我的代码中是否有任何错误,因为该值未正确写入？

Answer 1

尝试使用单字节值数组创建数据.

const uint8_t bytes[] = {0xDE};
NSData *data = [NSData dataWithBytes:bytes length:sizeof(bytes)];

这是创建任意常量数据的有用方法.对于更多字节,

const uint8_t bytes[] = {0x01,0x02,0x03,0x04,0x05};
NSData *data = [NSData dataWithBytes:bytes length:sizeof(bytes)];

如果要创建要使用变量发送的数据,我建议使用NSMutableData并附加所需的字节.它不是很漂亮,但它易于阅读/理解,尤其是当您在嵌入式端匹配打包结构时.以下示例来自BLE项目,我们正在制作一个简单的通信协议.

NSMutableData *data = [[NSMutableData alloc] init];

//pull out each of the fields in order to correctly
//serialize into a correctly ordered byte stream
const uint8_t start     = PKT_START_BYTE;
const uint8_t bitfield  = (uint8_t)self.bitfield;
const uint8_t frame     = (uint8_t)self.frameNumber;
const uint8_t size      = (uint8_t)self.size;

//append the individual bytes to the data chunk
[data appendBytes:&start    length:1];
[data appendBytes:&bitfield length:1];
[data appendBytes:&frame    length:1];
[data appendBytes:&size     length:1];

Answer 2

Swift 3.0：如果有人想知道 Swift 的格式略有不同，因为 writeValue 可以从数组中获取计数。

let value: UInt8 = 0xDE
let data = Data(bytes: [value])
peripheral.writeValue(data, for: characteristic, type: .withResponse)