ios如何修改系统音量

1.修改系统音量 MPVolumeView 系统提供的音量控件，它里面的MPVolumeSlider是私有的  但是可以获取它来改变他的value从而修改音量，如果不想要系统的音量改变的提示框，可以把MPVolumeView放在屏幕外面

​MPVolumeView*volumeView = [[MPVolumeViewalloc]init];

[self.viewaddSubview:volumeView];

UISlider* volumeViewSlider =nil;

for(UIView*viewin[volumeViewsubviews]){

if([view.class.descriptionisEqualToString:@"MPVolumeSlider"]){

volumeViewSlider = (UISlider*)view;

break;        }

}

floatsystemVolume = volumeViewSlider.value;

[volumeViewSlidersetValue:1.0fanimated:NO];

_volumeViewSlider= volumeViewSlider;

​[volumeViewSlider sendActionsForControlEvents:UIControlEventTouchUpInside];

2.监听系统音量的改变

NSError *error;

​[[NSNotificationCenter defaultCenter] addObserver:self                                                 selector:@selector(volumeChanged:)                                                     name:@"AVSystemController_SystemVolumeDidChangeNotification"                                                   object:nil];

[[UIApplication sharedApplication] beginReceivingRemoteControlEvents];//注，ios9上不加这一句会无效，加了这一句后，

//在移除通知时候加上这句[[UIApplication sharedApplication] endReceivingRemoteControlEvents];

-(void)volumeChanged:(NSNotification *)noti{

float volume =       [[[noti userInfo]           objectForKey:@"AVSystemController_AudioVolumeNotificationParameter"]         floatValue];

NSLog(@"volumn is %f", volume);

}