Understanding Bluetooth Audio Devices in iOS

As a developer working with iOS, you may have encountered the challenge of finding Bluetooth audio devices connected to your app. In this article, we will delve into the world of CoreBluetooth and External Accessory frameworks, exploring how to enumerate Bluetooth audio devices on an iPhone.

Introduction to CoreBluetooth and External Accessory Frameworks

CoreBluetooth is a framework that allows developers to access Bluetooth Low Energy (BLE) devices on iOS devices. It provides a high-level API for discovering, connecting, and managing BLE devices. On the other hand, the External Accessory framework is used to manage external accessories connected to an iPhone.

Both frameworks offer ways to discover connected devices, but with different approaches and limitations. In this article, we will focus on using CoreBluetooth to find Bluetooth audio devices.

Configuring Audio Session for Bluetooth Connections

Before we dive into finding Bluetooth audio devices, it’s essential to configure the audio session to allow Bluetooth connections that support audio. You can do this in your application delegate’s application(_:didFinishLaunchingWithOptions:) method.

#import <AVFoundation/AVFoundation.h>

- (BOOL)prepareAudioSession {
    // deactivate session
    BOOL success = [[AVAudioSession sharedInstance] setActive:NO error: nil];
    if (!success) {
        NSLog(@"deactivationError");
    }

    // set audio session category AVAudioSessionCategoryPlayAndRecord options AVAudioSessionCategoryOptionAllowBluetooth
    success = [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayAndRecord withOptions:AVAudioSessionCategoryOptionAllowBluetooth error:nil];
    if (!success) {
        NSLog(@"setCategoryError");
    }

    // activate audio session
    success = [[AVAudioSession sharedInstance] setActive:YES error: nil];
    if (!success) {
        NSLog(@"activationError");
    }

    return success;
}

Finding Bluetooth Audio Devices

To find Bluetooth audio devices, you need to use the scanForPeripheralsWithServices: method of CBCentralManager. However, this method only returns nearby peripherals that support a specific service. To get a list of all connected Bluetooth audio devices, you need to observe the AVAudioSessionRouteChangeNotification notification.

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(myRouteChangeSelector:)
                                             name:AVAudioSessionRouteChangeNotification
                                           object:nil];

In this method, we get the current route of the audio session and extract the inputs and outputs for that route. We then check if there are any BluetoothHFP (Hands-Free Profile) devices connected.

- (void)myRouteChangeSelector:(NSNotification*)notification {
    AVAudioSessionRouteDescription *currentRoute = [[AVAudioSession sharedInstance] currentRoute];
    NSArray *inputsForRoute = currentRoute.inputs;
    NSArray *outputsForRoute = currentRoute.outputs;

    // Check if there are any BluetoothHFP devices connected
    AVAudioSessionPortDescription *outPortDesc = [outputsForRoute objectAtIndex:0];
    NSLog(@"current outport type %@", outPortDesc.portType);
    AVAudioSessionPortDescription *inPortDesc = [inputsForRoute objectAtIndex:0];
    NSLog(@"current inPort type %@", inPortDesc.portType);
}

Handling Interruptions and Route Changes

To handle interruptions (such as phone calls or alarms) and route changes, you need to observe the AVAudioSessionInterruptionNotification notification.

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(myInterruptionSelector:)
                                             name:AVAudioSessionInterruptionNotification
                                           object:nil];

In this method, we handle the interruption and make sure to resume audio playback when the user is done with their phone call or alarm.

- (void)myInterruptionSelector:(NSNotification*)notification {
    // Handle interruption
    // Resume audio playback when user is done with call or alarm
}

Conclusion

In this article, we explored how to find Bluetooth audio devices in iOS using CoreBluetooth and External Accessory frameworks. We discussed the importance of configuring the audio session to allow Bluetooth connections that support audio and provided examples on how to enumerate Bluetooth audio devices.

To successfully implement this feature, you need to handle interruptions and route changes, which requires observing specific notifications. By following these steps, you can provide a comprehensive solution for your iOS app to detect and manage Bluetooth audio devices.

Additional Tips

• To improve the accuracy of finding Bluetooth audio devices, consider using a proximity API like corelocation or siri.
• When implementing this feature, make sure to test it thoroughly on different iPhone models and versions.
• Consider using a third-party library like AVAudioSessionDelegate to simplify your code.

By following these tips and understanding the intricacies of CoreBluetooth and External Accessory frameworks, you can create an app that effectively detects and manages Bluetooth audio devices.

Last modified on 2023-12-17