Sample ViewController to simulate simple Drag and Drop.

DragAndDropViewController.swift

import UIKit

class DragAndDropViewController: UIViewController, UIGestureRecognizerDelegate {
    private var sourceView: UIView!
    private var dropArea: UIView!

    private var objectSize = CGSize(width: 100, height: 100)
    private var originalPosition = CGPoint.zero

    override func loadView() {
        self.view = UIView()
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        setupView()
    }

    private func setupView() {
        // Initialize
        sourceView = UIView(frame: CGRect(origin: .zero, size: objectSize))
        sourceView.backgroundColor = .red

        dropArea = UIView(frame: CGRect(origin: CGPoint(x: 250, y: 500), size: objectSize))
        dropArea.backgroundColor = .blue

        // Add Gesture
        sourceView.addGestureRecognizer(UIPanGestureRecognizer(target: self, action: #selector(didLongPressSource)))

        // setup root
        view.addSubview(dropArea)
        view.addSubview(sourceView)
    }

    var touchOffset = CGPoint.zero

    @objc private func didLongPressSource(gesture: UIGestureRecognizer) {
        switch(gesture.state) {
        case .began:
            touchOffset = gesture.location(in: sourceView)

        case .changed:
            // 1. get moved position
            let location = gesture.location(in: view) - touchOffset
            // 2. Move there
            sourceView.frame.origin = location


        case .ended:
            // 1. get current position
            let location = gesture.location(in: view) - touchOffset
            // 2. check if we're closer to start or the end
            let distanceFromOrigin = location.distance(from: originalPosition)
            let distanceFromDropZone = location.distance(from: dropArea.frame.origin)
            let targetPosition = distanceFromOrigin > distanceFromDropZone ? dropArea.frame.origin : originalPosition
            // 3. move to the closest point
            UIView.animate(withDuration: 0.3) {
                self.sourceView.frame.origin = targetPosition
            }

        default:
            break
        }
    }
}

extension CGPoint {
    func distance(from anotherPoint: CGPoint) -> CGFloat {
        let dx = abs(x - anotherPoint.x)
        let dy = abs(y - anotherPoint.y)
        return sqrt(dx*dx + dy*dy)
    }

    static func +(_ one: CGPoint,_ other: CGPoint) -> CGPoint {
        return CGPoint(x: one.x + other.x, y: one.y + other.y)
    }

    static func -(_ one: CGPoint,_ other: CGPoint) -> CGPoint {
        return CGPoint(x: one.x - other.x, y: one.y - other.y)
    }
}

// To use this VC in a playground:
import PlaygroundSupport
PlaygroundPage.current.liveView = DragAndDropViewController()