新增 MPVolumeView

// Add MPVolumeView in a holder view
let mpVolumeHolderView = UIView(frame: CGRect(x: 0, y: view.bounds.midY, width: view.bounds.width, height: view.bounds.height))
// Set the holder view's background color to transparent
mpVolumeHolderView.backgroundColor = .clear
let mpVolume = MPVolumeView(frame: mpVolumeHolderView.bounds)
mpVolume.showsRouteButton = true
mpVolumeHolderView.addSubview(mpVolume)
view.addSubview(mpVolumeHolderView)
// the volume view is white, set the parent background to black to show it better in this example
view.backgroundColor = .black

!!! 一個非常重要的注意事項是 MPVolumeView 僅適用於實際裝置，而不適用於模擬器。