trying to flip a UIImage view but when flipping back Im receiving a nil

Question

Im trying to flip a UIImageView to its other side to reveal whats behind it. Everything works fine the first flip over, revealing the image behind it. The issue is when i try to flip it back to hide the image. I get an error that its trying to find a nil.Thanks for any help.

import UIKit

class ViewController: UIViewController {
@IBOutlet weak var mainLeftView: UIView!
@IBOutlet weak var back: UIImageView!
@IBOutlet weak var front: UIImageView!





override func viewDidLoad() {
    super.viewDidLoad()


    let singleTap = UITapGestureRecognizer(target: self, action: Selector("tappedItem"))
    singleTap.numberOfTapsRequired = 1







    mainLeftView.addGestureRecognizer(singleTap)
     mainLeftView.userInteractionEnabled = true;
    mainLeftView.addSubview(front)

}



var showingFront = true;

func tappedItem() {


   /*     TRIED METHOD NUMBER ONE


    var views: (front: UIImageView, back: UIImageView)

    if ((self.front.superview) != nil){
        views = (front: self.front, back: self.back)
    } else{
        views = (front: self.back, back: self.front)
    }
    UIView.transitionFromView(views.front, toView: views.back, duration: 1.0, options:UIViewAnimationOptions.TransitionFlipFromRight , completion: nil)

*/

  // METHOD NUMBER TWO


      if (showingFront){
      UIView.transitionFromView(front, toView: back, duration: 0.5, options: UIViewAnimationOptions.TransitionFlipFromRight, completion: nil)
        showingFront = false;
    }

    else{
        UIView.transitionFromView(back, toView: front, duration: 0.5, options: UIViewAnimationOptions.TransitionFlipFromLeft, completion: nil)
        showingFront = true;

    }

}

can you plz try like this http://stackoverflow.com/questions/9032331/ios-flip-animation-only-for-specific-view — Viral Savaj, Apr 16 '15 at 16:18
remove weak. swift default is strong let it be like that. second method looks good. — Uttam Sinha, Apr 16 '15 at 16:32
Uttam removing the weak works but it breaks the constraints i have on the two image views to mainLeftView. Sorry I didnt mention this before. — Antonio Lipiz, Apr 16 '15 at 16:40

score 0 · Answer 1 · answered Apr 16 '15 at 16:22

0

use strong rather than weak.

@IBOutlet strong var mainLeftView: UIView!
@IBOutlet strong var back: UIImageView!
@IBOutlet strong var front: UIImageView!

answered Apr 16 '15 at 16:22

casillas

16,351
19
115
215

using strong rather than weak works, but it breaks the constraints i have on the two image views to main left view – Antonio Lipiz Apr 16 '15 at 16:34
in your given code, there is no constraint mentioned. – casillas Apr 16 '15 at 16:35
yes sorry i didnt mention this. the two image views are constrained to mainLeftView. – Antonio Lipiz Apr 16 '15 at 16:39

score 0 · Answer 2 · answered Apr 16 '15 at 16:28

I accomplished something similar. I used 3 views. The first being a containerView, the other 2 being subviews within the container view.

You will need to keep track of the current state of the container view (isFlipped) to determine how to flip the container view. Once the animation is occurring simple hide the front or back view.

    if !containerView.isFlipped {
        UIView.transitionWithView(containerView, duration: 0.75, options: UIViewAnimationOptions.TransitionFlipFromLeft, animations: { () -> Void in
            frontView.hidden = true
            backView.hidden = false

            }, completion: { (completion:Bool) -> Void in
                containerView.isFlipped = true
        })
    } else {
        UIView.transitionWithView(containerView, duration: 0.75, options: UIViewAnimationOptions.TransitionFlipFromRight, animations: { () -> Void in
            frontView.hidden = false
            backView.hidden = true
            }, completion: { (completion:Bool) -> Void in
                containerView.isFlipped = false
        })
    }

trying to flip a UIImage view but when flipping back Im receiving a nil

2 Answers2