How to display UIView over keyboard in iOS

You can add that new subview to your application window.

func attach(sender : UIButton)
{
    // Calculate and replace the frame according to your keyboard frame
    var customView = UIView(frame: CGRect(x: 0, y: self.view.frame.size.height-300, width: self.view.frame.size.width, height: 300))
    customView.backgroundColor = UIColor.redColor()
    customView.layer.zPosition = CGFloat(MAXFLOAT)
    var windowCount = UIApplication.sharedApplication().windows.count
    UIApplication.sharedApplication().windows[windowCount-1].addSubview(customView);
}

Swift 4.0

let customView = UIView(frame: CGRect(x: 0, y: self.view.frame.size.height-300, width: self.view.frame.size.width, height: 300))
customView.backgroundColor = UIColor.red
customView.layer.zPosition = CGFloat(MAXFLOAT)
let windowCount = UIApplication.shared.windows.count
UIApplication.shared.windows[windowCount-1].addSubview(customView)

As Tamás Sengel said, Apple's guidelines does not support adding a view over the keyboard. The recommended way to add a view over keyboard in Swift 4 & 5 is:

1) Add view with your "Next" button in your storyboard as external view and connect in your class (see Explain Image), in my case:

IBOutlet private weak var toolBar: UIView!

2) For the textfield you want to add your custom view over keyboard, add it as accessory view in viewDidLoad:

override func viewDidLoad() {
    super.viewDidLoad()
    phoneNumberTextField.inputAccessoryView = toolBar
}

3) Add action for "Next" button:

@IBAction func nextButtonPressed(_ sender: Any) {
    descriptionTextView.becomeFirstResponder()

    // or -> phoneNumberTextField.resignFirstResponder()
}

Explain Image:

Method 2: Result with image

In TableView Controller - add stricked view at bottom

Please follow this great link to handle safe area for screens like iPhone X if you want to use this method(2). Article: InputAccessoryView and iPhone X

override var inputAccessoryView: UIView? {
    return toolBar
}

override var canBecomeFirstResponder: Bool {
    return true
}

Swift 4 version:

let customView = UIView(frame: CGRect(x: 0, y: self.view.frame.size.height - 300, width: self.view.frame.size.width, height: 300))
customView.backgroundColor = UIColor.red
customView.layer.zPosition = CGFloat(Float.greatestFiniteMagnitude)
UIApplication.shared.windows.last?.addSubview(customView)

The trick is to add the customView as a top subview to the UIWindow that holds the keyboard - and it happens to be the last window in UIApplication.shared.windows.