iOS开发之音乐播放----监听系统音量变化

需要在：didFinishLaunchingWithOptions:(NSDictionary *)launchOptions方法中加入一下监听事件：

    //监听系统音量控制
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(volumeChanged:)
                                                 name:@"AVSystemController_SystemVolumeDidChangeNotification"
                                               object:nil];
 
  
 
  
 然后实现对应的通知事件： 
  
 
  
 
  
- (void)volumeChanged:(NSNotification *)notification
{
    float volume =
    [[[notification userInfo]
      objectForKey:@"AVSystemController_AudioVolumeNotificationParameter"]
     floatValue];
    
    NSLog(@"%f", volume);
}