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Issue Info

Issue Description

UILabel constraints seem to break when animating the width getting smaller

.

The Setup

In my UIViewController I have 3 UIViews, stacked horizontally:
Box1 - Box2 - Box3

Box1 and Box3 have a specific size, and Box2 fills up the remaining space between them.

I also have a UILabel, centred at the middle of the screen, and with its size depending on the size of Box2.

// The UIView
box2.snp_makeConstraints { (make) in
            make.leading.equalTo(box1.snp_trailing)
            make.trailing.equalTo(box3.snp_leading)
            make.top.equalTo(box1.snp_top)
            make.bottom.equalTo(box1.snp_bottom)
}

// The label     
centerLabel.snp_makeConstraints { (make) in
            make.center.equalTo(self.view.snp_center).priorityRequired()
            make.size.equalTo(box2.snp_size)
}

I have a button that calls a toggle function. Either Box1 and Box3 get larger, thus shrinking Box2. Or Box1 and Box3 get smaller, thus expanding Box2.

The Label's size changes accordingly with Box2 and works perfectly well when Box2 is expanding.
The issue is when Box2 is shrinking: the label shrinks right away (not animated) and aligns with the left border of Box2 rather than staying centred.

// This is the toggle function
func changeConstraints(){

        self.box1.snp_updateConstraints(closure: { (make) in
            make.width.equalTo(CGRectGetWidth(self.box1.frame) == 50 ? 100 : 50)
        })

        self.box3.snp_updateConstraints(closure: { (make) in
            make.width.equalTo(CGRectGetWidth(self.box3.frame) == 50 ? 100 : 50)
        })

        UIView.animateWithDuration(1.2, animations: {
            self.view.layoutIfNeeded()
        })

    }

Any idea what's causing this? Am I overlooking something?