蓝牙实现流程：

1.建立中心管理者
2.扫描外设
3.连接外设
4.扫描外设的服务和特征
5.与外设进行数据交互

代码实现：

第一：建立中心管理者
首先：导入#import <CoreBluetooth/CoreBluetooth.h>框架
初始化CBCentralManager对象并设置代理以及队列，queue：nil，默认就是在主线程

<CBCentralManagerDelegate>
@property (nonatomic, strong) CBCentralManager *centralManager;
self.centralManager = [[CBCentralManager alloc] initWithDelegate:self queue:dispatch_get_main_queue()];

接着调用CBCentralManagerDelegate必须实现的方法- (void)centralManagerDidUpdateState:(CBCentralManager *)central

- (void)centralManagerDidUpdateState:(CBCentralManager *)central {
switch (central.state) {
            case CBCentralManagerStateUnknown:
                NSLog(@"CBCentralManagerStateUnknown");
                break;
            case CBCentralManagerStateResetting:
                NSLog(@"CBCentralManagerStateResetting");
                break;
            case CBCentralManagerStateUnsupported:
                NSLog(@"CBCentralManagerStateUnsupported");
                break;
            case CBCentralManagerStateUnauthorized:
                NSLog(@"CBCentralManagerStateUnauthorized");
                break;
            case CBCentralManagerStatePoweredOff:
                NSLog(@"CBCentralManagerStatePoweredOff");
                break;
            case CBCentralManagerStatePoweredOn:
                NSLog(@"CBCentralManagerStatePoweredOn");
                break;
            default:
                break;
        }
}

第二：扫描外设

- (void)centralManagerDidUpdateState:(CBCentralManager *)central {
    if (central.state == CBCentralManagerStatePoweredOn) {
        //扫描外设，第一个参数：nil，表示扫描所有外设，也可以根据CBUUID数组查找指定外设
        [self.centralManager scanForPeripheralsWithServices:nil options:nil];
    } else {
        NSLog(@"请打开蓝牙");
    }
}

扫描到外设之后，会调用此方法

- (void)centralManager:(CBCentralManager *)central didDiscoverPeripheral:(CBPeripheral *)peripheral advertisementData:(NSDictionary<NSString *, id> *)advertisementData RSSI:(NSNumber *)RSSI {
  //连接外设
}

第三：连接外设

@property (nonatomic, strong) CBPeripheral *peripheral;
- (void)centralManager:(CBCentralManager *)central didDiscoverPeripheral:(CBPeripheral *)peripheral advertisementData:(NSDictionary<NSString *, id> *)advertisementData RSSI:(NSNumber *)RSSI {
    NSLog(@"找到蓝牙外设 名称：%@",peripheral.name);
    
    if ([peripheral.name isEqualToString:@"要连接的蓝牙名称"]) {
        //这里要注意一点：peripheral在该方法里不被持有，调用结束后会被自动摧毁，保存外设，使其被持有
        self.peripheral = peripheral;
        //连接外设
        [self.centralManager connectPeripheral:peripheral options:nil];
    } else {
        NSLog(@"未找到要连接的外设");
    }
}

connectPeripheral方法后会执行以下代理方法

//外设连接成功
- (void)centralManager:(CBCentralManager *)central didConnectPeripheral:(CBPeripheral *)peripheral {
    NSLog(@"连接蓝牙成功");
    //设置代理以及查找服务
    [peripheral setDelegate:self];
    [peripheral discoverServices:nil];
}

//外设连接失败
- (void)centralManager:(CBCentralManager *)central didFailToConnectPeripheral:(CBPeripheral *)peripheral error:(NSError *)error {
    NSLog(@"连接失败");
}

//断开连接
- (void)centralManager:(CBCentralManager *)central didDisconnectPeripheral:(CBPeripheral *)peripheral error:(NSError *)error {
    NSLog(@"断开连接");
}

第四：扫描外设的服务和特征

- (void)centralManager:(CBCentralManager *)central didConnectPeripheral:(CBPeripheral *)peripheral {
    NSLog(@"连接蓝牙成功");
    //设置代理<CBPeripheralDelegate>以及查找服务
    [peripheral setDelegate:self];
    [peripheral discoverServices:nil];
}
#pragma mark- CBPeripheralDelegate
- (void)peripheral:(CBPeripheral *)peripheral didDiscoverServices:(NSError *)error {
    if (error) {
        NSLog(@"error: %@",error);
        return;
    }
    for (CBService *service in peripheral.services) {
        //扫描服务中的特征
        [peripheral discoverCharacteristics:nil forService:service];
    }
}

- (void)peripheral:(CBPeripheral *)peripheral didDiscoverCharacteristicsForService:(CBService *)service error:(NSError *)error {
    for (CBCharacteristic *characteristics in service.characteristics) {
        if ([characteristics.UUID isEqual:[CBUUID UUIDWithString:@"writeUUID"]]) {
            //向外设发送数据：data
            [peripheral writeValue:[NSData data] forCharacteristic:characteristics type:CBCharacteristicWriteWithResponse];
        } else if ([characteristics.UUID isEqual:[CBUUID UUIDWithString:@"readUUID"]]) {
            [peripheral readValueForCharacteristic:characteristics];
        } else if ([characteristics.UUID isEqual:[CBUUID UUIDWithString:@"notifyUUID"]]) {
            [peripheral setNotifyValue:YES forCharacteristic:characteristics];
        }
    }
}

第五：与外设进行数据交互

[self.peripheral writeValue:[NSData data] forCharacteristic:characteristics type:CBCharacteristicWriteWithResponse];

//获取characteristic的值
- (void)peripheral:(CBPeripheral *)peripheral didUpdateValueForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error {
    NSLog(@"收到数据：%@",characteristic.value);
    //此处对外设返回的数据进行处理
    
}