How do you set the hardware volume in an iPhone app?

Question

Some iPhone applications, such as Pandora seem to directly manipulate the hardware volume and respond to physical volume button. How is this done?

AudioSessionServic

Answer 1

They use the MPVolumeView, simple add it and it's makes the rest when the user touch it. Note: Doesn't work in iPhone Simulator. I think the release note also mentioned do not use it direct in Interface Builder.

MPVolumeView *volumeView = [[MPVolumeView alloc] initWithFrame:CGRectMake(25, 378, 270, 30)];
[self.view addSubview:volumeView];
[volumeView release];