Add observer for AVAudioSession.outputVolume

webrtc/modules/audio_device/ios/objc/RTCAudioSession.mm

 /*
  *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #import "webrtc/modules/audio_device/ios/objc/RTCAudioSession.h"
 
 #import <UIKit/UIKit.h>
 
 #include "webrtc/base/atomicops.h"
 #include "webrtc/base/checks.h"
 #include "webrtc/base/criticalsection.h"
 #include "webrtc/modules/audio_device/ios/audio_device_ios.h"
 
 #import "WebRTC/RTCLogging.h"
 #import "webrtc/modules/audio_device/ios/objc/RTCAudioSession+Private.h"
 #import "webrtc/modules/audio_device/ios/objc/RTCAudioSessionConfiguration.h"
 
 NSString * const kRTCAudioSessionErrorDomain = @"org.webrtc.RTCAudioSession";
 NSInteger const kRTCAudioSessionErrorLockRequired = -1;
 NSInteger const kRTCAudioSessionErrorConfiguration = -2;
+NSString * const kRTCAudioSessionOutputVolumeSelector = @"outputVolume";
 
 // This class needs to be thread-safe because it is accessed from many threads.
 // TODO(tkchin): Consider more granular locking. We're not expecting a lot of
 // lock contention so coarse locks should be fine for now.
 @implementation RTCAudioSession {
   rtc::CriticalSection _crit;
   AVAudioSession *_session;
   volatile int _activationCount;
   volatile int _lockRecursionCount;
   volatile int _webRTCSessionCount;
@@ skipping 42 matching lines @@
     // hint to enable or disable audio that is secondary.
     [center addObserver:self
                selector:@selector(handleSilenceSecondaryAudioHintNotification:)
                    name:AVAudioSessionSilenceSecondaryAudioHintNotification
                  object:nil];
     // Also track foreground event in order to deal with interruption ended situation.
     [center addObserver:self
                selector:@selector(handleApplicationDidBecomeActive:)
                    name:UIApplicationDidBecomeActiveNotification
                  object:nil];
+    [_session addObserver:self
+               forKeyPath:kRTCAudioSessionOutputVolumeSelector
+                  options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld
+                  context:nil];
+
     RTCLog(@"RTCAudioSession (%p): init.", self);
   }
   return self;
 }
 
 - (void)dealloc {
   [[NSNotificationCenter defaultCenter] removeObserver:self];
+  [_session removeObserver:self forKeyPath:kRTCAudioSessionOutputVolumeSelector context:nil];
   RTCLog(@"RTCAudioSession (%p): dealloc.", self);
 }
 
 - (NSString *)description {
   NSString *format =
       @"RTCAudioSession: {\n"
        "  category: %@\n"
        "  categoryOptions: %ld\n"
        "  mode: %@\n"
        "  isActive: %d\n"
@@ skipping 690 matching lines @@
 }
 
 - (void)audioSessionDidDeactivate:(AVAudioSession *)session {
   if (_session != session) {
     RTCLogError(@"audioSessionDidDeactivate called on different AVAudioSession");
   }
   self.isActive = NO;
   [self decrementActivationCount];
 }
 
+- (void)observeValueForKeyPath:(NSString *)keyPath
+                      ofObject:(id)object
+                        change:(NSDictionary *)change
+                       context:(void *)context {
+  if (object == _session) {
+    NSNumber *newVolume = change[NSKeyValueChangeNewKey];
+    [self notifyAudioVolumeDidChange:newVolume.floatValue];
+  } else {
+    [super observeValueForKeyPath:keyPath ofObject:object change:change

[tkchin_webrtc, 2017/05/25 23:01:00]

nit: either all args on same line, or all on different lines

+                          context:context];
+  }
+}
+
 - (void)notifyDidBeginInterruption {
   for (auto delegate : self.delegates) {
     SEL sel = @selector(audioSessionDidBeginInterruption:);
     if ([delegate respondsToSelector:sel]) {
       [delegate audioSessionDidBeginInterruption:self];
     }
   }
 }
 
 - (void)notifyDidEndInterruptionWithShouldResumeSession:
@@ skipping 57 matching lines @@
 
 - (void)notifyDidStopPlayOrRecord {
   for (auto delegate : self.delegates) {
     SEL sel = @selector(audioSessionDidStopPlayOrRecord:);
     if ([delegate respondsToSelector:sel]) {
       [delegate audioSessionDidStopPlayOrRecord:self];
     }
   }
 }
 
+- (void)notifyAudioVolumeDidChange:(float)volume {

[tkchin_webrtc, 2017/05/25 23:01:00]

nit: notifyDidChangeOutputVolume

+  RTCLog(@"AudioVolumeDidChange to %f", volume);

[tkchin_webrtc, 2017/05/25 23:01:00]

Would place this at the point where you know it changed (ie the observer
method), rather than the function that is called to notify.

Please call it output volume - audio volume could mean many different things.

+  for (auto delegate : self.delegates) {
+    SEL sel = @selector(audioSession:didChangeOutputVolume:);
+    if ([delegate respondsToSelector:sel]) {
+      [delegate audioSession:self didChangeOutputVolume:volume];
+    }
+  }
+}
+
 @end