A floating button on iOS for http://stackoverflow.com/q/34777558/77567

FloatingViewController.swift

import UIKit

class FloatingButtonController: UIViewController {

    private(set) var button: UIButton!

    required init?(coder aDecoder: NSCoder) {
        fatalError()
    }

    init() {
        super.init(nibName: nil, bundle: nil)
        window.windowLevel = CGFloat.max
        window.hidden = false
        window.rootViewController = self

        NSNotificationCenter.defaultCenter().addObserver(self, selector: "keyboardDidShow:", name: UIKeyboardDidShowNotification, object: nil)
    }

    private let window = FloatingButtonWindow()

    override func loadView() {
        let view = UIView()
        let button = UIButton(type: .Custom)
        button.setTitle("Floating", forState: .Normal)
        button.setTitleColor(UIColor.greenColor(), forState: .Normal)
        button.backgroundColor = UIColor.whiteColor()
        button.layer.shadowColor = UIColor.blackColor().CGColor
        button.layer.shadowRadius = 3
        button.layer.shadowOpacity = 0.8
        button.layer.shadowOffset = CGSize.zero
        button.sizeToFit()
        button.frame = CGRect(origin: CGPointMake(10, 10), size: button.bounds.size)
        button.autoresizingMask = []
        view.addSubview(button)
        self.view = view
        self.button = button
        window.button = button

        let panner = UIPanGestureRecognizer(target: self, action: "panDidFire:")
        button.addGestureRecognizer(panner)
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        snapButtonToSocket()
    }

    func panDidFire(panner: UIPanGestureRecognizer) {
        let offset = panner.translationInView(view)
        panner.setTranslation(CGPoint.zero, inView: view)
        var center = button.center
        center.x += offset.x
        center.y += offset.y
        button.center = center

        if panner.state == .Ended || panner.state == .Cancelled {
            UIView.animateWithDuration(0.3) {
                self.snapButtonToSocket()
            }
        }
    }

    func keyboardDidShow(note: NSNotification) {
        window.windowLevel = 0
        window.windowLevel = CGFloat.max
    }

    private func snapButtonToSocket() {
        var bestSocket = CGPoint.zero
        var distanceToBestSocket = CGFloat.infinity
        let center = button.center
        for socket in sockets {
            let distance = hypot(center.x - socket.x, center.y - socket.y)
            if distance < distanceToBestSocket {
                distanceToBestSocket = distance
                bestSocket = socket
            }
        }
        button.center = bestSocket
    }

    private var sockets: [CGPoint] {
        let buttonSize = button.bounds.size
        let rect = view.bounds.insetBy(dx: 4 + buttonSize.width / 2, dy: 4 + buttonSize.height / 2)
        let sockets: [CGPoint] = [
            CGPointMake(rect.minX, rect.minY),
            CGPointMake(rect.minX, rect.maxY),
            CGPointMake(rect.maxX, rect.minY),
            CGPointMake(rect.maxX, rect.maxY),
            CGPointMake(rect.midX, rect.midY)
        ]
        return sockets
    }

}

private class FloatingButtonWindow: UIWindow {

    var button: UIButton?

    init() {
        super.init(frame: UIScreen.mainScreen().bounds)
        backgroundColor = nil
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }


    private override func pointInside(point: CGPoint, withEvent event: UIEvent?) -> Bool {
        guard let button = button else { return false }
        let buttonPoint = convertPoint(point, toView: button)
        return button.pointInside(buttonPoint, withEvent: event)
    }
    
}

can you please update code for iOS 13 and above when scene delegate is used

import UIKit

class FloatingButtonController: UIViewController {

    private(set) var button: UIButton!

    required init?(coder aDecoder: NSCoder) {
        fatalError()
    }

    init(scene: UIWindowScene) {
        window = FloatingButtonWindow(scene: scene)
        super.init(nibName: nil, bundle: nil)
        window.windowLevel = UIWindow.Level(rawValue: CGFloat.greatestFiniteMagnitude)
        window.isHidden = false
        window.rootViewController = self

        NotificationCenter.default.addObserver(self, selector: #selector(keyboardDidShow(note:)), name: UIResponder.keyboardDidShowNotification, object: nil)
    }

    private let window: FloatingButtonWindow

    override func loadView() {
        let view = UIView()
        let button = UIButton(type: .custom)
        button.setTitle("Floating", for: .normal)
        button.setTitleColor(UIColor.green, for: .normal)
        button.backgroundColor = UIColor.white
        button.layer.shadowColor = UIColor.black.cgColor
        button.layer.shadowRadius = 3
        button.layer.shadowOpacity = 0.8
        button.layer.shadowOffset = CGSize.zero
        button.sizeToFit()
        button.frame = CGRect(origin: CGPoint(x: 10, y: 10), size: button.bounds.size)
        button.autoresizingMask = []
        view.addSubview(button)
        self.view = view
        self.button = button
        window.button = button

        let panner = UIPanGestureRecognizer(target: self, action: #selector(panDidFire(panner:)))
        button.addGestureRecognizer(panner)
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        snapButtonToSocket()
    }

    @objc func panDidFire(panner: UIPanGestureRecognizer) {
        let offset = panner.translation(in: view)
        panner.setTranslation(CGPoint.zero, in: view)
        var center = button.center
        center.x += offset.x
        center.y += offset.y
        button.center = center

        if panner.state == .ended || panner.state == .cancelled {
            UIView.animate(withDuration: 0.3) {
                self.snapButtonToSocket()
            }
        }
    }

    @objc func keyboardDidShow(note: NSNotification) {
        window.windowLevel = UIWindow.Level(rawValue: 0)
        window.windowLevel = UIWindow.Level(rawValue: CGFloat.greatestFiniteMagnitude)
    }

    private func snapButtonToSocket() {
        var bestSocket = CGPoint.zero
        var distanceToBestSocket = CGFloat.infinity
        let center = button.center
        for socket in sockets {
            let distance = hypot(center.x - socket.x, center.y - socket.y)
            if distance < distanceToBestSocket {
                distanceToBestSocket = distance
                bestSocket = socket
            }
        }
        button.center = bestSocket
    }

    private var sockets: [CGPoint] {
        let buttonSize = button.bounds.size
        let rect = view.bounds.insetBy(dx: 4 + buttonSize.width / 2, dy: 4 + buttonSize.height / 2)
        let sockets: [CGPoint] = [
            CGPoint(x: rect.minX, y: rect.minY),
            CGPoint(x: rect.minX, y: rect.maxY),
            CGPoint(x: rect.maxX, y: rect.minY),
            CGPoint(x: rect.maxX, y: rect.maxY),
            CGPoint(x: rect.midX, y: rect.midY)
        ]
        return sockets
    }

}

private class FloatingButtonWindow: UIWindow {

    var button: UIButton?

    init(scene: UIWindowScene) {
        super.init(windowScene: scene)
        backgroundColor = nil
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }


    fileprivate override func point(inside point: CGPoint, with event: UIEvent?) -> Bool {
        guard let button = button else { return false }
        let buttonPoint = convert(point, to: button)
        return button.point(inside: buttonPoint, with: event)
    }

}

in SceneDelegate:

var floatingButtonController: FloatingButtonController?

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    guard let scene = (scene as? UIWindowScene) else { return }
    floatingButtonController = FloatingButtonController(scene: scene)
    floatingButtonController?.button.addTarget(self, action: #selector(floatingButtonWasTapped), for: .touchUpInside)
}