iOS開發之音樂播放----監聽系統音量變化

需要在：didFinishLaunchingWithOptions:(NSDictionary *)launchOptions方法中加入一下監聽事件：

<pre name="code" class="objc">    //監聽系統音量控制
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(volumeChanged:)
                                                 name:@"AVSystemController_SystemVolumeDidChangeNotification"
                                               object:nil];
           

然後實作對應的通知事件：

- (void)volumeChanged:(NSNotification *)notification
{
    float volume =
    [[[notification userInfo]
      objectForKey:@"AVSystemController_AudioVolumeNotificationParameter"]
     floatValue];
    
    NSLog(@"%f", volume);
}