在BLE设备和BLE中心设备之间建立连接后，可以使用BLE协议中的多特征值来进行数据交换。多特征值允许在同一连接中发送和接收多个数据。以下是使用多特征值的示例代码：

1. 创建一个可以存储多个特征值的服务

static BLEService* pService = new BLEService(UUID_SERVICE);
static BLECharacteristic* pChar1 = new BLECharacteristic(UUID_CHAR1, BLECharacteristic::PROPERTY_READ | BLECharacteristic::PROPERTY_WRITE);
static BLECharacteristic* pChar2 = new BLECharacteristic(UUID_CHAR2, BLECharacteristic::PROPERTY_READ | BLECharacteristic::PROPERTY_NOTIFY);
static BLECharacteristic* pChar3 = new BLECharacteristic(UUID_CHAR3, BLECharacteristic::PROPERTY_WRITE);

pService->addCharacteristic(pChar1);
pService->addCharacteristic(pChar2);
pService->addCharacteristic(pChar3);

2. 在连接成功后，向特征值中添加数据或从特征值中读取数据

void onConnect(BLEServer *pServer) {
  BLECharacteristic* pCharacteristic = pService->getCharacteristic(UUID_CHAR1);
  pCharacteristic->setValue("Hello");
  
  pCharacteristic = pService->getCharacteristic(UUID_CHAR3);
  uint8_t data[2] = {0x01, 0x02};
  pCharacteristic->setValue(data, sizeof(data));
}

void onRead(BLECharacteristic *pCharacteristic) {
  std::string value = pCharacteristic->getValue();
  Serial.println(value.c_str());
}

void onWrite(BLECharacteristic *pCharacteristic) {
  uint8_t data[10];
  int len = pCharacteristic->getValue(data, sizeof(data));
  Serial.print("Received data:");
  for (int i = 0; i < len; i++) {
    Serial.print(data[i]);
  }
}

3. 启用通知以接收其他设备发送到特征值的数据

void startNotify(BLEServer* pServer) {
  BLECharacteristic* pCharacteristic = pService->getCharacteristic(UUID_CHAR2);
  pCharacteristic->registerForNotify(onNotify);