1. 前言

如果您阅读本文的时候有障碍或者有疑问，可以评论区留言或者看看本专栏的前部分内容。

从这一章节开始，我们不再仅仅讲解源码当中的例子了，因为越来越深入了。

特征的读写是BLE通讯中较为常用的数据交换手段了，因为源码给的例子中没有专门针对这个部分的内容，所以在这里我们自己制定一个实战DEMO。

2. 涉及到的API

2.1. write_gatt_char

写特征，在对特征进行写时，我们要提前获取到它的UUID或者Handle或者其他能体现特征身份的相关信息。在API里面有这样的解释道：

char_specifier (BleakGATTCharacteristic, int, str or UUID): The characteristic to writeto, specified by either integer handle, UUID or directly by theBleakGATTCharacteristic object representing it.

完整的API源码是这样的：

async def write_gatt_char(self,char_specifier: Union[BleakGATTCharacteristic, int, str, uuid.UUID],data: Union[bytes, bytearray, memoryview],response: bool = False,) -> None:"""Perform a write operation of the specified GATT characteristic.Args:char_specifier (BleakGATTCharacteristic, int, str or UUID): The characteristic to writeto, specified by either integer handle, UUID or directly by theBleakGATTCharacteristic object representing it.data (bytes or bytearray): The data to send.response (bool): If write-with-response operation should be done. Defaults to `False`."""if not isinstance(char_specifier, BleakGATTCharacteristic):characteristic = self.services.get_characteristic(char_specifier)else:characteristic = char_specifierif not characteristic:raise BleakError("Characteristic {} was not found!".format(char_specifier))response = (GattWriteOption.WRITE_WITH_RESPONSEif responseelse GattWriteOption.WRITE_WITHOUT_RESPONSE)buf = Buffer(len(data))buf.length = buf.capacitywith memoryview(buf) as mv:mv[:] = data_ensure_success(await characteristic.obj.write_value_with_result_async(buf, response),None,f"Could not write value {data} to characteristic {characteristic.handle:04X}",)

2.2. read_gatt_char

读特征，在对特征进行读取时，同样需要提前获取到它的UUID或者Handle或者其他能体现特征身份的相关信息。

完整的API源码是这样的：

async def read_gatt_char(self,char_specifier: Union[BleakGATTCharacteristic, int, str, uuid.UUID],**kwargs,) -> bytearray:"""Perform read operation on the specified GATT characteristic.Args:char_specifier (BleakGATTCharacteristic, int, str or UUID): The characteristic to read from,specified by either integer handle, UUID or directly by theBleakGATTCharacteristic object representing it.Keyword Args:use_cached (bool): ``False`` forces Windows to read the value from thedevice again and not use its own cached value. Defaults to ``False``.Returns:(bytearray) The read data."""use_cached = kwargs.get("use_cached", False)if not isinstance(char_specifier, BleakGATTCharacteristic):characteristic = self.services.get_characteristic(char_specifier)else:characteristic = char_specifierif not characteristic:raise BleakError("Characteristic {0} was not found!".format(char_specifier))value = bytearray(_ensure_success(await characteristic.obj.read_value_async(BluetoothCacheMode.CACHEDif use_cachedelse BluetoothCacheMode.UNCACHED),"value",f"Could not read characteristic handle {characteristic.handle}",))logger.debug(f"Read Characteristic {characteristic.handle:04X} : {value}")return value

3. 实战

现在要实现一个这样的功能：
用nRF Connect模拟一个设备，将GATT SERVICE里面一个特征设置成同时可读可写的属性。然后使用Bleak的在电脑上对刚刚模拟的设备进行读写操作（先写数据，再读取出来，看看是不是相同的内容）。

3.1 nRF Connect模拟设备

将Generic Access中的设备名字设置成可读可写属性：

3.2 代码编写

这次我们基于官方例子 service_explorer.py 进行二次开发，因为在对特征进行读取之前，我们需要先获取到它的句柄或者UUID相关信息。

对nRF Connect模拟的设备进行连接时，最好是通过名字进行扫描及搜索。对 service_explorer.py 进行一番简化及修改：

通过设备名字扫描设备，获取到其设备地址
通过扫描获取到的设备发起连接

import sys
import platform
import asyncio
import loggingfrom bleak import BleakClient
from bleak import BleakScannerlogger = logging.getLogger(__name__)DEVICE_NAME = "dabai"async def main():device = await BleakScanner.find_device_by_filter(lambda d, ad: d.name and d.name.lower() == DEVICE_NAME.lower())print(device)async with BleakClient(device.address) as client:logger.info(f"Connected: {client.is_connected}")for service in client.services:logger.info(f"[Service] {service}")for char in service.characteristics:if "read" in char.properties:try:value = bytes(await client.read_gatt_char(char.uuid))logger.info(f"\t[Characteristic] {char} ({','.join(char.properties)}), Value: {value}")except Exception as e:logger.error(f"\t[Characteristic] {char} ({','.join(char.properties)}), Value: {e}")else:value = Nonelogger.info(f"\t[Characteristic] {char} ({','.join(char.properties)}), Value: {value}")for descriptor in char.descriptors:try:value = bytes(await client.read_gatt_descriptor(descriptor.handle))logger.info(f"\t\t[Descriptor] {descriptor}) | Value: {value}")except Exception as e:logger.error(f"\t\t[Descriptor] {descriptor}) | Value: {e}")if __name__ == "__main__":logging.basicConfig(level=logging.INFO)asyncio.run(main())

运行结果，目前仅对目标进行了发现服务特征的操作：

EE:A6:84:0B:23:20: dabai
INFO:bleak.backends.winrt.client:Services resolved for BleakClientWinRT (EE:A6:84:0B:23:20)
INFO:__main__:Connected: True
INFO:__main__:[Service] 00001800-0000-1000-8000-00805f9b34fb (Handle: 1): Generic Access Profile
INFO:__main__:  [Characteristic] 00002a00-0000-1000-8000-00805f9b34fb (Handle: 2):  (read,write), Value: b'dabai'
INFO:__main__:  [Characteristic] 00002a01-0000-1000-8000-00805f9b34fb (Handle: 4):  (read), Value: b'\xc1\x00'
INFO:__main__:  [Characteristic] 00002a04-0000-1000-8000-00805f9b34fb (Handle: 6):  (read), Value: b'P\x00\xa0\x00\x00\x00\x90\x01'
INFO:__main__:  [Characteristic] 00002aa6-0000-1000-8000-00805f9b34fb (Handle: 8):  (read), Value: b'\x01'
INFO:__main__:[Service] 00001801-0000-1000-8000-00805f9b34fb (Handle: 10): Generic Attribute Profile
INFO:__main__:  [Characteristic] 00002a05-0000-1000-8000-00805f9b34fb (Handle: 11):  (indicate), Value: None
INFO:__main__:          [Descriptor] 00002902-0000-1000-8000-00805f9b34fb (Handle: 13): Client Characteristic Configuration) | Value: b'\x02\x00'
INFO:__main__:[Service] 0000180d-0000-1000-8000-00805f9b34fb (Handle: 14): Heart Rate
INFO:__main__:  [Characteristic] 00002a37-0000-1000-8000-00805f9b34fb (Handle: 15):  (notify), Value: None
INFO:__main__:          [Descriptor] 00002902-0000-1000-8000-00805f9b34fb (Handle: 17): Client Characteristic Configuration) | Value: b'\x00\x00'
INFO:__main__:  [Characteristic] 00002a38-0000-1000-8000-00805f9b34fb (Handle: 18):  (read), Value: b'\x03'
INFO:__main__:[Service] 0000180f-0000-1000-8000-00805f9b34fb (Handle: 20): Battery Service
INFO:__main__:  [Characteristic] 00002a19-0000-1000-8000-00805f9b34fb (Handle: 21):  (read), Value: b'a'
INFO:__main__:[Service] 0000180a-0000-1000-8000-00805f9b34fb (Handle: 23): Device Information
INFO:__main__:  [Characteristic] 00002a29-0000-1000-8000-00805f9b34fb (Handle: 24):  (read), Value: b'YFTech'
INFO:__main__:  [Characteristic] 00002a24-0000-1000-8000-00805f9b34fb (Handle: 26):  (read), Value: b'COROS M1D_4R9'
INFO:__main__:  [Characteristic] 00002a25-0000-1000-8000-00805f9b34fb (Handle: 28):  (read), Value: b'4B948172B1E2'
INFO:__main__:  [Characteristic] 00002a27-0000-1000-8000-00805f9b34fb (Handle: 30):  (read), Value: b'UVWbejJZpqrsPtwuvxy'
INFO:__main__:  [Characteristic] 00002a28-0000-1000-8000-00805f9b34fb (Handle: 32):  (read), Value: b'V 2.70.0'
INFO:__main__:[Service] 6e400001-b5a3-f393-e0a9-77656c6f6f70 (Handle: 34): Unknown
INFO:__main__:  [Characteristic] 6e400003-b5a3-f393-e0a9-77656c6f6f70 (Handle: 35):  (notify), Value: None
INFO:__main__:          [Descriptor] 00002902-0000-1000-8000-00805f9b34fb (Handle: 37): Client Characteristic Configuration) | Value: b'\x00\x00'
INFO:__main__:  [Characteristic] 6e400002-b5a3-f393-e0a9-77656c6f6f70 (Handle: 38):  (write-without-response,write), Value: None
INFO:__main__:[Service] 6e400001-b5a3-f393-e0a9-77757c7f7f70 (Handle: 40): Unknown
INFO:__main__:  [Characteristic] 6e400003-b5a3-f393-e0a9-77757c7f7f70 (Handle: 41):  (notify), Value: None
INFO:__main__:          [Descriptor] 00002902-0000-1000-8000-00805f9b34fb (Handle: 43): Client Characteristic Configuration) | Value: b'\x00\x00'
INFO:__main__:  [Characteristic] 6e400002-b5a3-f393-e0a9-77757c7f7f70 (Handle: 44):  (write-without-response,write), Value: None
INFO:__main__:[Service] 6e400001-b5a3-f393-e0a9-e50e24dcca9e (Handle: 46): Nordic UART Service
INFO:__main__:  [Characteristic] 6e400003-b5a3-f393-e0a9-e50e24dcca9e (Handle: 47):  (notify), Value: None
INFO:__main__:          [Descriptor] 00002902-0000-1000-8000-00805f9b34fb (Handle: 49): Client Characteristic Configuration) | Value: b'\x00\x00'
INFO:__main__:  [Characteristic] 6e400002-b5a3-f393-e0a9-e50e24dcca9e (Handle: 50):  (write-without-response,write), Value: None
INFO:__main__:[Service] 0000fee7-0000-1000-8000-00805f9b34fb (Handle: 52): Tencent Holdings Limited
INFO:__main__:  [Characteristic] 0000fea1-0000-1000-8000-00805f9b34fb (Handle: 53):  (read,notify,indicate), Value: b'\x01\x00\x00\x00'
INFO:__main__:          [Descriptor] 00002902-0000-1000-8000-00805f9b34fb (Handle: 55): Client Characteristic Configuration) | Value: b'\x00\x00'
INFO:__main__:  [Characteristic] 0000fea2-0000-1000-8000-00805f9b34fb (Handle: 56):  (read,write,indicate), Value: b"\x01\x10'\x00"
INFO:__main__:          [Descriptor] 00002902-0000-1000-8000-00805f9b34fb (Handle: 58): Client Characteristic Configuration) | Value: b'\x00\x00'
INFO:__main__:  [Characteristic] 0000fec9-0000-1000-8000-00805f9b34fb (Handle: 59):  (read), Value: b'\xee\xa6\x84\x0b# '
INFO:__main__:[Service] 00001814-0000-1000-8000-00805f9b34fb (Handle: 61): Running Speed and Cadence
INFO:__main__:  [Characteristic] 00002a53-0000-1000-8000-00805f9b34fb (Handle: 62):  (notify), Value: None
INFO:__main__:          [Descriptor] 00002902-0000-1000-8000-00805f9b34fb (Handle: 64): Client Characteristic Configuration) | Value: b'\x00\x00'
INFO:__main__:  [Characteristic] 00002a54-0000-1000-8000-00805f9b34fb (Handle: 65):  (read), Value: b'\x05\x00'
INFO:__main__:[Service] 00001816-0000-1000-8000-00805f9b34fb (Handle: 67): Cycling Speed and Cadence
INFO:__main__:  [Characteristic] 00002a5b-0000-1000-8000-00805f9b34fb (Handle: 68):  (notify), Value: None
INFO:__main__:          [Descriptor] 00002902-0000-1000-8000-00805f9b34fb (Handle: 70): Client Characteristic Configuration) | Value: b'\x00\x00'
INFO:__main__:  [Characteristic] 00002a5c-0000-1000-8000-00805f9b34fb (Handle: 71):  (read), Value: b'\x07\x00'
INFO:__main__:  [Characteristic] 00002a5d-0000-1000-8000-00805f9b34fb (Handle: 73):  (read), Value: b'\x04'
INFO:__main__:  [Characteristic] 00002a55-0000-1000-8000-00805f9b34fb (Handle: 75):  (write,indicate), Value: None
INFO:__main__:          [Descriptor] 00002902-0000-1000-8000-00805f9b34fb (Handle: 77): Client Characteristic Configuration) | Value: b'\x00\x00'

我们主要在意这部分输出结果：

可以得知我们设置的这个特征的UUID是这样的

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