Update storyboard constraint using code

Question

I have a UIImage in code that I would like to enlarge vertically when a button is pressed. The UIImage is fully constrained in the storyboard and I would like to change its height when the button is pressed.

I have linked the UIImage and its height constraint in the code:

    @IBOutlet weak var botBotCons: NSLayoutConstraint!
    @IBOutlet weak var botBot: UIImageView!

Then

@IBAction func testButton(sender: UIBarButtonItem) {
    println("testButton pressed")
    self.botBotCons.constant = 68   //or +=62 as its current constant is 6
    self.view.layoutIfNeeded()
}

I get the testButton pressed message in the console, but the image doesn't resize. What am I doing wrong? Do I need to change something in the storyboard as well?

Answer 1

You should to call layoutIfNeeded within the animation block. Apple actually recommends you call it once before the animation block to ensure that all pending layout operations have been completed. I just checked it with the resizing of button - everything works fine.

@IBOutlet weak var myBtn: UIButton!
@IBOutlet weak var btnHeight: NSLayoutConstraint!
@IBOutlet weak var btnWidth: NSLayoutConstraint!


@IBAction func resizeBtn(sender: AnyObject) {
    self.myBtn.titleEdgeInsets = UIEdgeInsetsMake(0, 0, 0, 0)

    self.view.layoutIfNeeded()
    self.btnHeight.constant += 50
    self.btnWidth.constant += 50

    UIView.animateWithDuration(0.7, animations: {
        self.view.layoutIfNeeded()
    })
}

P.S. make sure that other constraints don't block your changes.