获取系统当前音量 和 监听系统音量 ios

-(float) getVolumeLevel
{MPVolumeView*slide =[MPVolumeViewnew];UISlider*volumeViewSlider;for(UIView*view in[slide subviews]){if([[[view class] description] isEqualToString:@"MPVolumeSlider"]){
            volumeViewSlider =(UISlider*) view;}}float val =[volumeViewSlider value];[slide release];return val;}

That should get you the current volume level. 1 is max volume, 0 is no volume. Note: no UI elements need to be displayed for this to work. Also note current volume level is relative to headphones or speakers (meaning, the two volume levels are different, and this gets you whichever the device is currently using. This doesn't answer your question regarding receiving notifications of when volume changes.

AVSystemController

+ (id)sharedAVSystemController;

- (void)getActiveCategoryVolume:(float*)outVolume andName:(NSString**)outName;

Returns the volumn and name of the active category. Tells you whether headphones are plugged in.

Notifications

Sends a AVSystemController_HeadphoneJackIsConnectedDidChangeNotification notification when the user plus in or unplugs headphones.

Sends a AVSystemController_SystemVolumeDidChangeNotification notification when the system volume has changed (via up/down buttons, mute switch, or programatically)

        [[NSNotificationCenterdefaultCenter] addObserver:self

                                                 selector:@selector(volumeChanged:)

                                                     name:@"AVSystemController_SystemVolumeDidChangeNotification"

                                                   object:nil];

 

-(void)volumeChanged:(NSNotification *)notification {  [volumeViewSlider setValue:[[[notification userInfo] objectForKey:@"AVSystemController_AudioVolumeNotificationParameter"] floatValue]]; }

 

 

 

-(void)volumeChanged:(NSNotification *)notification {  [volumeViewSlider setValue:[[[notification userInfo] objectForKey:@"AVSystemController_AudioVolumeNotificationParameter"] floatValue]]; }