iPhone SDK - 如果按下硬件按钮，如何禁用音量指示器视图？

Question

Is there a way to prevent the volume indicator view form showing if you press the volume up/down hardware buttons?

It's needed for a demo app only. So the method don't need to be App Store safe.

Answer 1

It works like that:

• play a silent file
• add a volume View to your main view
• send the view to back

eg

 NSString *url = [[NSBundle mainBundle]
                       pathForResource:@"silent" ofType:@"mp3"];
 MPMoviePlayerController *moviePlayer = [[MPMoviePlayerController alloc]
                       initWithContentURL:[NSURL URLWithString:url]];
 [moviePlayer play];

 MPVolumeView *volumeView = [[[MPVolumeView alloc] initWithFrame:
                       CGRectMake(0, 0, 1, 1)] autorelease];
 [self.view addSubview:volumeView]; 
 [self.view sendSubviewToBack:volumeView];

Answer 2

IIRC, the presence of a MPVolumeView inhibits the display of the volume indicator overlay. Try sticking it the relevant view and seeing if this is the case.

Then you can try various tricks to make it effectively invisible:

• Make it hidden (or make a superview hidden).
• Set its alpha (or the alpha of a superview) to 0, or 0.01, or so.
• Move it off-screen
• Move it almost off-screen (eg so only the top-left pixel is on screen)
• Stick it under another view.
• Stick it in a subview with clipsToBounds=ON, and move it outside those bounds
• Set volumeView.layer.mask to a new (thus fully-transparent) CALayer. Set volumeView.userInteractionEnabled = NO.

All of these are theoretically detectable by MPVolumeView, but I suspect some of them will work.

Answer 3

- (void)viewDidLoad
 {
  [super viewDidLoad];

  //get current volume level
  oldVolume= [[MPMusicPlayerController applicationMusicPlayer] volume];

  //hide volume indicator         
  MPVolumeView *volumeView = [[[MPVolumeView alloc] initWithFrame:
                             CGRectMake(0, 0, 1, 1)] autorelease];

  musicController=[MPMusicPlayerController applicationMusicPlayer];
  [self.view addSubview:volumeView];
  [self.view sendSubviewToBack:volumeView];
  [NSTimer scheduledTimerWithTimeInterval:0.02 target:self selector:@selector(volume) userInfo:nil repeats:YES];
}

- (void)volume
{
  if ([musicController volume]>oldVolume || [musicController volume]<oldVolume) {
    [musicController setVolume:oldVolume];
    // do some stuff here and the volume level never changes, just like volume action in camera app
   }
}