Understanding CoreBluetooth and iOS Pairing

Introduction

CoreBluetooth (CB) is a framework provided by Apple for developers to access the Bluetooth functionality on iOS devices. It allows applications to discover, connect, and communicate with nearby Bluetooth devices. In this article, we will explore how to check an iPhone’s paired Bluetooth devices using CB.

The Challenges

The question at hand is to retrieve all the currently paired Bluetooth devices without performing any Bluetooth scanning. This should not require any additional hardware or resources.

However, there are a few challenges that need to be addressed:

• The retrieveConnectedPeripherals method does not work as expected because it requires the device to be powered on and in a connected state.
• There is no built-in way to retrieve paired devices without scanning for nearby devices.

Understanding Bluetooth State

The CBCentralManager class has an state property that indicates the current state of the Bluetooth connection. The possible states are:

Solving the Problem

To solve this problem, we need to implement a solution that checks for paired devices when the device is powered on.

The provided code snippet shows how to initialize the CBCentralManager and retrieve connected peripherals:

- (void)viewDidLoad {
    [super viewDidLoad];
    self.centralManager = [[CBCentralManager alloc] initWithDelegate:self queue:nil];
}

- (void)centralManagerDidUpdateState:(CBCentralManager *)manager {
   switch (manager.state) {
        case CBCentralManagerStatePoweredOn:
             NSLog(@"CBCentral Manager powered on");
             [self.centralManager retrieveConnectedPeripherals];
             break;
        case CBCentralManagerStatePoweredOff:
             NSLog(@"Bluetooth is turned off, cannot connect peripherals");
             break;
}

However, the code snippet still fails to log any paired devices. The problem lies in the fact that the retrieveConnectedPeripherals method requires a Bluetooth scan to determine which devices are connected.

Alternative Solution

To solve this problem, we can implement an alternative solution using a timer:

- (void)viewDidLoad {
    [super viewDidLoad];
    self.centralManager = [[CBCentralManager alloc] initWithDelegate:self queue:nil];

    // Set up the timer
    dispatch_time_t now = dispatch_time(NULL, 0);
    dispatch_repeating_timer_t timer;
    dispatch_register_repeating_timer(now, ^{
        [self centralManager:centralManager didRetrieveConnectedPeripherals:peripherals];
    }, 1.0 / 10.0, 1.0 / 10.0);

}

- (void)centralManager:(CBCentralManager *)central didRetrieveConnectedPeripherals:(NSArray *)peripherals {
    NSLog(@"didRetrieveConnectedPeripherals called");
    for (CBPeripheral *a in peripherals){
        NSLog(a.name); //just log the name for now to see if it recognized it
    }
}

However, this alternative solution requires a Bluetooth scan which is not desirable.

Additional Considerations

There are additional considerations when implementing CoreBluetooth applications:

• Make sure that the iOS device has Bluetooth 4.0 or later.
• The CBCentralManager works for devices with Bluetooth 4.0 and later.
• Be aware that some peripherals may not support Bluetooth 4.0, so your application will not work on those devices.

Conclusion

In conclusion, CoreBluetooth provides a powerful framework for accessing Bluetooth functionality on iOS devices. However, the retrieveConnectedPeripherals method requires the device to be powered on and in a connected state. To solve this problem, we need to implement an alternative solution that uses a timer to retrieve paired devices.

Understanding Bluetooth states and implementing additional solutions can help improve the performance of CoreBluetooth applications.

Last modified on 2023-08-10