How do i add dynamic behaviour in NSObject class : Swift

Question

I'm trying to create a custom alertview with dynamic behaviour using UIDynamicAnimator in NSObject class using swift,While adding UISnapBehaviour to a view in NSObject class init method snap behaviour is not working,For instance look at the below code

import UIKit

class DynamicBehaviour: NSObject {

var Animator:UIDynamicAnimator!
var TargetView:UIView!
var TestView:UIView!

override init() {
    super.init()
}

init(SourceViews:UIView) {
    super.init()

    TestView = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
    TestView.backgroundColor = UIColor.blueColor()
    TargetView.addSubview(TestView)

    Animator = UIDynamicAnimator(referenceView: TargetView)
    let snapBehavior: UISnapBehavior = UISnapBehavior(item: TestView, snapToPoint: TargetView.center)
    Animator.addBehavior(snapBehavior)

  }
}

"TestView" is added as subview to "Target" but snap behaviour is not working.

I tried the same code in ObjectiveC

#import "DynamicBehaviour.h"
#import <UIKit/UIKit.h>

@interface DynamicBehaviour ()
@property(nonatomic,strong)UISnapBehavior * Snap_behaviour;
@property (nonatomic,strong)UIDynamicAnimator * Animator;


@end
@implementation DynamicBehaviour

-(instancetype)initWithSourceView:(UIView *)TargetView{
   if (self = [super init]) {
      UIView * TestView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 100,     100)];
      TestView.backgroundColor = [UIColor blueColor];
      [TargetView addSubview:TestView];

      self.Animator = [[UIDynamicAnimator    alloc]initWithReferenceView:TargetView];
       self.Snap_behaviour = [[UISnapBehavior alloc]initWithItem:TestView snapToPoint:TargetView.center];
       [self.Animator addBehavior:self.Snap_behaviour];
   }
  return self;
  }


 @end

it works fine,the "TestView" snaps to the centre of TargetView.I don't know whats wrong with swift code.

Here's what I've tried:

1. The dynamic effect is working fine when coded in UIViewController class,problem exist only while subclassing NSObject in swift.
2. I have tried the other dynamic behaviours such as UIGravityBehavior the same problem exists in swift.
3. Done the same sample work in ObjectiveC object class its working fine,I've attached the working ObjC code too.

It seems that the problem may exist in init method or variable decleration am not sure about that However, I don't know how to fix that problem. I've read through many articles on the internet. I've also searched StackOverflow. Please help.

Answer 1

Your code in Swift is not exactly the same as Objective-C code: Objective-C code has strong reference Snap_behaviour, but Swift code has only local readonly variable. Here is the Swift equivalent:

class DynamicBehaviour: NSObject {

    var Animator:UIDynamicAnimator!
    var snapBehaviour:UISnapBehavior!
    var TargetView:UIView!
    var TestView:UIView!

    override init() {
        super.init()
    }

    init(SourceViews:UIView) {
        super.init()

        TestView = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
        TestView.backgroundColor = UIColor.blueColor()
        TargetView.addSubview(TestView)

        Animator = UIDynamicAnimator(referenceView: TargetView)
        snapBehaviour = UISnapBehavior(item: TestView, snapToPoint: TargetView.center)
        Animator.addBehavior(snapBehaviour)

    }
}

Usually I use UIDynamicBehaviour as base class for combined behaviors like this

class CombinedBehavior: UIDynamicBehavior {

    lazy var collider: UICollisionBehavior = {
        let lazilyCreatedCollider = UICollisionBehavior()
        lazilyCreatedCollider.translatesReferenceBoundsIntoBoundary = true
        lazilyCreatedCollider.collisionMode = UICollisionBehaviorMode.Everything
        return lazilyCreatedCollider
    }()

    lazy var itemBehavior: UIDynamicItemBehavior = {
        let lazilyCreatedBehavior = UIDynamicItemBehavior()
        lazilyCreatedBehavior.allowsRotation = true
        lazilyCreatedBehavior.elasticity = 0
        lazilyCreatedBehavior.resistance = 100
        lazilyCreatedBehavior.angularResistance = 100
        lazilyCreatedBehavior.friction = 100
        return lazilyCreatedBehavior
    }()

    override init() {
        super.init()
        addChildBehavior(collider)
        addChildBehavior(itemBehavior)
    }

    func addBarrier(path: UIBezierPath, named name: String) {
        collider.removeBoundaryWithIdentifier(name)
        collider.addBoundaryWithIdentifier(name, forPath: path)
    }

    func addView(view: UIView) {
        dynamicAnimator?.referenceView?.addSubview(view)
        collider.addItem(view)
        itemBehavior.addItem(view)
    }

    func removeView(view: UIView) {
        collider.removeItem(view)
        itemBehavior.removeItem(view)
        view.removeFromSuperview()
    }
}

Put this code in your controller

lazy var animator: UIDynamicAnimator = {
    let lazilyCreatedDynamicAnimator = UIDynamicAnimator(referenceView: self.view) // or any view you needed
    // if you need delegate in your controller uncomment this
    //        lazilyCreatedDynamicAnimator.delegate = self
    return lazilyCreatedDynamicAnimator
}()

var combinedBehavior = CombinedBehavior()

override func viewDidLoad() {
    // your other code
    animator.addBehavior(combinedBehavior)
}