Set MPVolumeView slider thumb position as device volume

I use MPVolumeView to generate a horizontal slider which allows me to manage the volume of the audio being played. It works great. However, at initialization, I want the slider takes the position corresponding to volume of the device and not 0.5, the default:

Here is the code I have done:

func volumeSlider() {

    let parentVolumeView = MPVolumeView(frame: volumeParentView.bounds)

    for view in parentVolumeView.subviews {
        if (view as UIView).description.rangeOfString("MPVolumeSlider") != nil {
            mpVolumeSlider = view as! UISlider
            print("mpVolumeSlider.value : ", mpVolumeSlider.value)

            // Tried to set mpVolumeSlider.value to volume device, but didn't work, show : 0.0
            // mpVolumeSlider.value = AVAudioSession.sharedInstance().outputVolume
        }
        // Remove device volume indicator
        self.view!.addSubview(parentVolumeView)
    }

    let thumbImage = UIImage(named: "slider-image")
    slider?.setThumbImage(thumbImage, forState: .Normal)
}

Assign your slider's value to to AVAudioSession.sharedInstance().outputVolume on init or in viewDidLoad of your view controller. Remember to import AVFoundation to use AVAudioSession.

Alternatively, you can programmatically initialize your MPVolumeView instead of having it as an outlet. I believe that is the source of your issue.