本地外设数据⽤用 CBMutableService 和 CBMutableCharacteristic 对象表⽰示

设置⼀一个本地外设并与它交互数据时,你需要处理本地外设的多个服务和特征的版本。在 Core Bluetooth 框架,本地外设的服务⽤用 CBMutableService 对象表 ⽰示。类似的,本地外设的特征⽤用 CBMuableCharacteristic 对象表⽰示。 图 1-7 阐明了本地外设服务和特征的基本机构。

主机通常要完成的任务

BLE 中扮演主机⾓角⾊色的设备要完成⼤大量通⽤用的任务--例如,发现和连接可以⽤用的外设,探索外设,与外设交互数据。相对⽽而⾔言,扮演外设的⾓角⾊色也需要完成⼀一些 与主机不同的通⽤用的任务,例如发布和⼲⼴广播服务,响应读写数据,处理已连接的主机的请求。
本章将学习如何使⽤用 Core Bluetooth 完成 BLE 主机端的通⽤用任务。基于代码的⽰示例可以帮助你⽤用本地设备扮演主机的⾓角⾊色。具体来说你可以学习到:

  启动主机管理对象

  发现和连接⼲⼴广播的外设

  连接之后探索外设数据

  给外设服务的⼀一些特征值发送读写请求

  订阅特征值并在他们更新时得到通知

下⼀一章将会学习如何⽤用本地设备扮演外设⾓角⾊色。

本章的⽰示例代码简单⽽而抽象,在你实际的应⽤用中需要对其做适当的修改来完善。许多跟主机相关的⾼高级主题会再后⾯面的章节讲述。

启动主机管理

CBCentralManager 对象时本地主机设备⾯面向对象的表⽰示,完成 BLE 传输前需要分配和初始化⼀一个主机管理实例。你可以通过调⽤用CBCentralManager类的 initWithDelegate:queue:options: ⽅方法初始化主机管理对象,如下所⽰示:

 myCentralManager =

 [[CBCentralManager alloc] initWithDelegate:self queue:nil options:nil];

[myCentralManager scanForPeripheralsWithServices:nil options:nil];

-(void)centralManager:(CBCentralManager *)central

didDiscoverPeripheral:(CBPeripheral *)peripheral

    advertisementData:(NSDictionary *)advertisementData

                 RSSI:(NSNumber *)RSSI {

   NSLog(@"Discovered %@", peripheral.name);

   ...

当你发现你想连接的外设后,停⽌止扫描其它设备以节约电量。

[myCentralManager stopScan];

 NSLog(@"Scanning stopped");

[myCentralManager connectPeripheral:peripheral options:nil];

- (void)centralManager:(CBCentralManager *)central

 didConnectPeripheral:(CBPeripheral *)peripheral {

 NSLog(@"Peripheral connected");

 ...

在与外设交互之前,需要设置外设的委托以确保期望的回调⽅方法能响应,如下所⽰示:

peripheral.delegate = self;

[peripheral discoverServices:nil];

- (void)peripheral:(CBPeripheral *)peripheral

 didDiscoverServices:(NSError *)error {

 for (CBService *service in peripheral.services) {

     NSLog(@"Discovered service %@", service);

... } ...

NSLog(@"Discovering characteristics for service %@", interestingService);

 [peripheral discoverCharacteristics:nil forService:interestingService];

- (void)peripheral:(CBPeripheral *)peripheral

 didDiscoverCharacteristicsForService:(CBService *)service

          error:(NSError *)error {

 for (CBCharacteristic *characteristic in service.characteristics) {

     NSLog(@"Discovered characteristic %@", characteristic);

... } ...

NSLog(@"Reading value for characteristic %@", interestingCharacteristic);

 [peripheral readValueForCharacteristic:interestingCharacteristic];

- (void)peripheral:(CBPeripheral *)peripheral

 didUpdateValueForCharacteristic:(CBCharacteristic *)characteristic

          error:(NSError *)error {

 NSData *data = characteristic.value;

 // parse the data as needed

 ...

 [peripheral setNotifyValue:YES forCharacteristic:interestingCharacteristic];

- (void)peripheral:(CBPeripheral *)peripheral

 didUpdateNotificationStateForCharacteristic:(CBCharacteristic *)characteristic

          error:(NSError *)error {

 if (error) {

     NSLog(@"Error changing notification state: %@",

        [error localizedDescription]);

NSLog(@"Writing value for characteristic %@", interestingCharacteristic); [peripheral writeValue:dataToWrite forCharacterist

 ic:interestingCharacteristic

  type:CBCharacteristicWriteWithResponse];

- (void)peripheral:(CBPeripheral *)peripheral

  didWriteValueForCharacteristic:(CBCharacteristic *)characteristic

            error:(NSError *)error {

 if (error) {

       NSLog(@"Error writing characteristic value: %@",

           [error localizedDescription]);

} ...

  启动外设管理对象

  启动外设的服务和特征

  发布服务和特征到设备的本地数据库

  ⼲⼴广播服务

  响应已连接的主机的读写请求。

  发送更新的特征值给订阅了的主机

myPeripheralManager =

 [[CBPeripheralManager alloc] initWithDelegate:self queue:nil options:nil];

CBUUID *heartRateServiceUUID = [CBUUID UUIDWithString: @"180D"];

$ uuidgen

 71DA3FD1-7E10-41C1-B16F-4430B506CDE7

CBUUID *myCustomServiceUUID =

 [CBUUID UUIDWithString:@"71DA3FD1-7E10-41C1-B16F-4430B506CDE7"];

myCharacteristic =

 [[CBMutableCharacteristic alloc] initWithType:myCharacteristicUUID

  properties:CBCharacteristicPropertyRead

  value:myValue permissions:CBAttributePermissionsReadable];

myService = [[CBMutableService alloc] initWithType:myServiceUUID primary:YES];

创建按服务之后,你可以通过设置服务的特征数组来关联⼀一个特征,如下所⽰示:

myService.characteristics = @[myCharacteristic];