Is there an event for when the headphones are unplugged?

During a test, a client noticed that video playback in the iPhone pauses when headphones are unplugged. He w开发者_如何学运维anted similar functionality for audio playback, and maybe the ability to pop up a message.

Does anyone know if there's an event of some kind I could hook into to make this possible?

See Responding to Route Changes from the Audio Session Programming Guide.

This changed with iOS 7, you just need to listen to the notification named AVAudioSessionRouteChangeNotification

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

Swift 3.0 @snakeoil's solution:

    NotificationCenter.default.addObserver(self, selector: #selector(YourViewController.yourMethodThatShouldBeCalledOnChange), name: NSNotification.Name.AVAudioSessionRouteChange, object: nil)

Here's the full implementation I eventually used for sending events when the headphones are plugged in (and unplugged).

There was a fair amount of complexity I needed to deal with to ensure things still worked after the app was returned from the background.

CVAudioSession.h file

#import <Foundation/Foundation.h>

#define kCVAudioInputChangedNotification @"kCVAudioInputChangedNotification"
#define kCVAudioInterruptionEnded @"kCVAudioInterruptionEnded"

@interface CVAudioSession : NSObject
+(void) setup;
+(void) destroy;
+(NSString*) currentAudioRoute;
+(BOOL) interrupted;
@end

CVAudioSession.m file

#import "CVAudioSession.h"
#import <AudioToolbox/AudioToolbox.h>

@implementation CVAudioSession

static BOOL _isInterrupted = NO;

+(void) setup {
    NSLog(@"CVAudioSession setup");

    // Set up the audio session for recording
    OSStatus error = AudioSessionInitialize(NULL, NULL, interruptionListener, (__bridge void*)self);

    if (error) NSLog(@"ERROR INITIALIZING AUDIO SESSION! %ld\n", error);
    if (!error) {
        UInt32 category = kAudioSessionCategory_RecordAudio; // NOTE CANT PLAY BACK WITH THIS
        error = AudioSessionSetProperty(kAudioSessionProperty_AudioCategory, sizeof(category), &category);
        if (error) NSLog(@"couldn't set audio category!");

        error = AudioSessionAddPropertyListener(kAudioSessionProperty_AudioRouteChange, propListener, (__bridge void*) self);
        if (error) NSLog(@"ERROR ADDING AUDIO SESSION PROP LISTENER! %ld\n", error);
        UInt32 inputAvailable = 0;
        UInt32 size = sizeof(inputAvailable);

        // we do not want to allow recording if input is not available
        error = AudioSessionGetProperty(kAudioSessionProperty_AudioInputAvailable, &size, &inputAvailable);
        if (error) NSLog(@"ERROR GETTING INPUT AVAILABILITY! %ld\n", error);

        // we also need to listen to see if input availability changes
        error = AudioSessionAddPropertyListener(kAudioSessionProperty_AudioInputAvailable, propListener, (__bridge void*) self);
        if (error) NSLog(@"ERROR ADDING AUDIO SESSION PROP LISTENER! %ld\n", error);

        error = AudioSessionSetActive(true);
        if (error) NSLog(@"CVAudioSession: AudioSessionSetActive (true) failed");
    }
}

+ (NSString*) currentAudioRoute {
    UInt32 routeSize = sizeof (CFStringRef);
    CFStringRef route;

    AudioSessionGetProperty (kAudioSessionProperty_AudioRoute,
                             &routeSize,
                             &route);

    NSString* routeStr = (__bridge NSString*)route;
    return routeStr;
}

+(void) destroy {
    NSLog(@"CVAudioSession destroy");

    // Very important - remove the listeners, or we'll crash when audio routes etc change when we're no longer on screen
    OSStatus stat = AudioSessionRemovePropertyListenerWithUserData(kAudioSessionProperty_AudioRouteChange, propListener, (__bridge void*)self);
    NSLog(@".. AudioSessionRemovePropertyListener kAudioSessionProperty_AudioRouteChange returned %ld", stat);

    stat = AudioSessionRemovePropertyListenerWithUserData(kAudioSessionProperty_AudioInputAvailable, propListener, (__bridge void*)self);
    NSLog(@".. AudioSessionRemovePropertyListener kAudioSessionProperty_AudioInputAvailable returned %ld", stat);

    AudioSessionSetActive(false); // disable audio session.
    NSLog(@"AudioSession is now inactive");
}

+(BOOL) interrupted {
    return _isInterrupted;
}

// Called when audio is interrupted for whatever reason. NOTE: doesn't always call the END one..
void interruptionListener(  void *  inClientData,
                          UInt32    inInterruptionState) {

    if (inInterruptionState == kAudioSessionBeginInterruption)
    {
        _isInterrupted = YES;

        NSLog(@"CVAudioSession: interruptionListener kAudioSessionBeginInterruption. Disable audio session..");

        // Try just deactivating the audiosession..
        OSStatus rc = AudioSessionSetActive(false);
        if (rc) {
            NSLog(@"CVAudioSession: interruptionListener kAudioSessionBeginInterruption - AudioSessionSetActive(false) returned %.ld", rc);
        } else {
            NSLog(@"CVAudioSession: interruptionListener kAudioSessionBeginInterruption - AudioSessionSetActive(false) ok.");
        }



    } else if (inInterruptionState == kAudioSessionEndInterruption) {

        _isInterrupted = NO;

        // Reactivate the audiosession
        OSStatus rc = AudioSessionSetActive(true);
        if (rc) {
            NSLog(@"CVAudioSession: interruptionListener kAudioSessionEndInterruption - AudioSessionSetActive(true) returned %.ld", rc);
        } else {
            NSLog(@"CVAudioSession: interruptionListener kAudioSessionEndInterruption - AudioSessionSetActive(true) ok.");   
        }

        [[NSNotificationCenter defaultCenter] postNotificationName:kCVAudioInterruptionEnded object:(__bridge NSObject*)inClientData userInfo:nil];
    }
}

// This is called when microphone or other audio devices are plugged in and out. Is on the main thread
void propListener(  void *                  inClientData,
                  AudioSessionPropertyID    inID,
                  UInt32                  inDataSize,
                  const void *            inData)
{
    if (inID == kAudioSessionProperty_AudioRouteChange)
    {
        CFDictionaryRef routeDictionary = (CFDictionaryRef)inData;
        CFNumberRef reason = (CFNumberRef)CFDictionaryGetValue(routeDictionary, CFSTR(kAudioSession_AudioRouteChangeKey_Reason));
        SInt32 reasonVal;
        CFNumberGetValue(reason, kCFNumberSInt32Type, &reasonVal);
        if (reasonVal != kAudioSessionRouteChangeReason_CategoryChange)
        {
            NSLog(@"CVAudioSession: input changed");
            [[NSNotificationCenter defaultCenter] postNotificationName:kCVAudioInputChangedNotification object:(__bridge NSObject*)inClientData userInfo:nil];
        }
    }
    else if (inID == kAudioSessionProperty_AudioInputAvailable)
    {
        if (inDataSize == sizeof(UInt32)) {
            UInt32 isAvailable = *(UInt32*)inData;

            if (isAvailable == 0) {
                NSLog(@"AUDIO RECORDING IS NOT AVAILABLE");
            }
        }
    }
}

@end