what is the relationship between external accessory and protocol string - ios

Question

I have to say sorry before, my english's not good.
I'm working on a project related to "external accessory framework".
I need to fetch some data stream from our product through a "USB to lightning" adapter.
I've been spinning my wheel for several days.
My question here is "what's the exact way to use the framework".
I found something on apple dev forum:
pic
Does it mean that if i have a "USB to lightning" adapter and its protocol string(For now, we're not going to make our own adapter, we plan to work with another company), then I plug our product to it, my app would be notified of the attachment or removal of the accessory.
Am i right?
I'm confusing right now, cause a colleague of mine contacted a adapter vendor, and they told her there is NO such thing called "protocol string".
I guess for some reason they just don't want us to know.
thanks!

Answer 1

You have set up these notifications for connection. Make you make connection through BT or USB.
/* Setup notification monitor */
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(handleAccessoryConnectNotification:) name:EAAccessoryDidConnectNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(handleAccessoryDisconnectNotification:) name:EAAccessoryDidDisconnectNotification object:nil];
/* Turn on EA notifications */
[[EAAccessoryManager sharedAccessoryManager] registerForLocalNotifications];
Once connection establishes you will get a call back with accessory info.
- (void) handleAccessoryConnectNotification:(NSNotification*)notification
{
NSDictonary *earInfo = notification.userInfo;
Print(#“Accessory Info: %#”,earInfo);
// Get connected Accessory object.
EAAccessory* currentAccessory = eaInfo[#"EAAccessoryKey"];
// Create Session with base Protocol with Accessory.
EASession* currentEASession = [[EASession alloc] initWithAccessory:currentAccessory forProtocol:“com.accessory.base”];
/* Open input and output steam */
if ( self.currentEASession.inputStream && self.currentEASession.outputStream)
{
[[currentEASession inputStream] setDelegate:self];
[[currentEASession inputStream] scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
[[currentEASession inputStream] open];
[[currentEASession outputStream] setDelegate:self];
[[currentEASession outputStream] scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
[[currentEASession outputStream] open];
}
}
- (void)handleAccessoryDisconnectNotification:(NSNotification*)notification {
Print(#“Accessory Info: %#”notification.userInfo);
}
# Read and Write data delegate method
- ( void ) stream: ( NSStream * ) aStream handleEvent: ( NSStreamEvent ) eventCode {
#try
{
switch ( eventCode )
{
case NSStreamEventOpenCompleted:{
Print(#“[%s] NSStreamEventOpenCompleted",__PRETTY_FUNCTION__);
break;
}
case NSStreamEventHasSpaceAvailable:
{
/* Write data */
break;
}
case NSStreamEventHasBytesAvailable:
{
//TODO
/* Read data */
static uint8_t buffer[65536];
NSInteger n = 65536;
while (n == 65536)
{
n = [self.currentEASession.inputStream read:buffer maxLength:65536];
}
break;
}
case NSStreamEventErrorOccurred:
{
//TODO
Print(#"[%s] NSStreamEventErrorOccurred",__PRETTY_FUNCTION__);
break;
}
case NSStreamEventEndEncountered:
{
//TODO
Print(#"[%s] NSStreamEventEndEncountered",__PRETTY_FUNCTION__);
break;
}
default:
{
break;
}
}
}
#catch (NSException *exception)
{
}
}

Answer 2

Relation between external accessory and protocol is.
When you connect iOS device with accessory. You have to create a session between accessory and iOS device to read and write data. Protocol string will identifier unique connection between accessory and iOS device for sharing and writing data.
Same time one accessory can be connected with multiple iOS devices. Each device will have a unique connection or session in between and it will identify through protocol.