NSLayoutConstraint animation finishes instantly

Question

I have a very simple project, I want to animate the right margin on a label, however when I try it, it finishes instantly.

strCriteria = Brandtype & " And " & strGeneric & " And " & strManufacturer

The project is here:

https://www.dropbox.com/s/9a0v0906riunkww/test2222.zip?dl=0

Am I missing something obvious?

Update #1

It seems it's a problem with UILabels specifically, a standard UIView, or UIButton animates fine....so whats wrong with a UILabel?

Update #2

If I set the UILabel View Content Mode to Center, then it works fine, but it doesn't look very smooth...very strange.

Answer 1

I may be off the mark here, but it looks to me as though your animation routine just does ArgumentError: wrong number of arguments (1 for 0) , which will cause the screen to redraw instantly. You need to change some animatable parameter of the UIView in order to see something move. Like setNeedslayout, perhaps. The animatable properties of UIView are listed here.

Answer 2

尝试使用self.view.setNeedsLayout()

替换动画片段中的self.view.layoutIfNeeded()

@IBAction func onDo(sender:UIButton) {
    self.testConstraint.constant = 40.0

    UIView.animateWithDuration(2.0, animations: { () -> Void in

        self.view.layoutIfNeeded()

        }) { (complete:Bool) -> Void in

    }
}