UIImages or UIViews are not colliding each other in iOS Swift? - ios

Question

I am trying to collide two UIViews each other for using pan gesture. Now i can able to drag one view but when dragging view to next view its collide each other. It goes behind other view.
Here is the screenshot result:
Here is the code I used to drag, pan and collide of physics property.
import UIKit
class ViewController: UIViewController {
var greenSquare: UIView?
var redSquare: UIView?
var animator: UIDynamicAnimator?
var snap: UISnapBehavior!
var panGesture = UIPanGestureRecognizer()
#IBAction func pan(_ sender: UIPanGestureRecognizer) {
let tapPoint: CGPoint = sender.location(in: view)
if (snap != nil) {
animator?.removeBehavior(snap)
}
snap = UISnapBehavior(item: greenSquare!, snapTo: tapPoint)
animator?.addBehavior(snap)
}
override func viewDidLoad() {
super.viewDidLoad()
var dimen = CGRect(x: 25, y: 25, width: 120, height: 120)
greenSquare = UIView(frame: dimen)
greenSquare?.backgroundColor = UIColor.green
dimen = CGRect(x: 130, y: 25, width: 100, height: 100)
redSquare = UIView(frame: dimen)
redSquare?.backgroundColor = UIColor.red
self.view.addSubview(greenSquare!)
self.view.addSubview(redSquare!)
animator = UIDynamicAnimator(referenceView: self.view)
let gravity = UIGravityBehavior(items: [greenSquare!, redSquare!])
let direction = CGVector(dx: 0.0, dy: 1.0)
gravity.gravityDirection = direction
let boundries = UICollisionBehavior(items: [greenSquare!, redSquare!])
boundries.translatesReferenceBoundsIntoBoundary = true
let bounce = UIDynamicItemBehavior(items: [greenSquare!, redSquare!])
bounce.elasticity = 0.5
animator?.addBehavior(bounce)
animator?.addBehavior(boundries)
animator?.addBehavior(gravity)
panGesture = UIPanGestureRecognizer(target: self, action:#selector(draggedView(sender:)))
greenSquare?.isUserInteractionEnabled = true
greenSquare?.addGestureRecognizer(panGesture)
}
#objc func draggedView(sender:UIPanGestureRecognizer){
let translation = sender.translation(in: self.view)
greenSquare?.center = CGPoint(x: (greenSquare?.center.x)! + translation.x, y: (greenSquare?.center.y)! + translation.y)
sender.setTranslation(CGPoint.zero, in: self.view)
}
}//class`
Anyone can help me out this.

Answer 1

The issue is that the animator only recognizes the collision at the origin of the greenSquare. In this case it is at the top of the screen. You can update the collision location on the animator after you move the greenSquare. Add animator?.updateItem(usingCurrentState: greenSquare!)
to the end of the draggedView method. You do not need to use UISnapBehavior for this so you can remove the IBAction func pan method at the top of your code. The updateItem(usingCurrentState:) call will reset where the collision barrier is when you are moving the view manually and it is not being done by the physics engine.