A simple helper class to check and get notified if a USB device is connected/disconnected

EYUSBDeviceConnectivity.h

// erkanyildiz
// 20160311-1158
//
// EYUSBDeviceConnectivity.h

#import <Foundation/Foundation.h>

@interface EYUSBDeviceConnectivity : NSObject
+ (instancetype)sharedInstance;
@property (nonatomic, copy) void (^onDeviceConnect)(NSNotification* notification);
@property (nonatomic, copy) void (^onDeviceDisconnect)(NSNotification* notification);
@property (nonatomic, readonly) BOOL isDeviceConnected;
@end

EYUSBDeviceConnectivity.m

// erkanyildiz
// 20160311-1158
//
// EYUSBDeviceConnectivity.m

#import "EYUSBDeviceConnectivity.h"
#import <ExternalAccessory/ExternalAccessory.h>

@implementation EYUSBDeviceConnectivity
+ (instancetype)sharedInstance
{
    static EYUSBDeviceConnectivity *s_sharedInstance = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{s_sharedInstance = self.new;});
    return s_sharedInstance;
}

- (instancetype)init
{
    if (self = [super init])
    {
        [NSNotificationCenter.defaultCenter addObserver:self
                                               selector:@selector(accessoryDidConnect:)
                                                   name:EAAccessoryDidConnectNotification
                                                 object:nil];
    
        [NSNotificationCenter.defaultCenter addObserver:self
                                               selector:@selector(accessoryDidDisconnect:)
                                                   name:EAAccessoryDidDisconnectNotification
                                                 object:nil];
    
        [EAAccessoryManager.sharedAccessoryManager registerForLocalNotifications];
    
        //NOTE: check if device already connected on app launch, if so post notification manually
        if([self isDeviceConnected])
        {
            EAAccessory* accessory = EAAccessoryManager.sharedAccessoryManager.connectedAccessories.firstObject;
            //NOTE: supposing only one accessory is connected
        
            NSNotification* notification = [NSNotification notificationWithName:EAAccessoryDidConnectNotification object:EAAccessoryManager.sharedAccessoryManager userInfo:@{@"EAAccessoryKey":accessory}];

            //NOTE: to make sure it is performed on next run loop, so blocks will be set.
            [self performSelector:@selector(accessoryDidConnect:) withObject:notification afterDelay:0.0];
        }
    }
    
    return self;
}


- (BOOL)isDeviceConnected
{
    return EAAccessoryManager.sharedAccessoryManager.connectedAccessories.count > 0;
}


- (void)accessoryDidConnect:(NSNotification*)aNotification
{
    if(self.onDeviceConnect)
    {
        self.onDeviceConnect(aNotification);
    }
}


- (void)accessoryDidDisconnect:(NSNotification*)aNotification
{
    if(self.onDeviceDisconnect)
    {
        self.onDeviceDisconnect(aNotification);
    }
}

@end