如何在 Swift 中以编程方式创建约束？

Question

I am trying to set up the width of a UIButton using this code:

constraintButtonPlayWidth = NSLayoutConstraint(item: buttonPlay,
        attribute: NSLayoutAttribute.Width,
        relatedBy: NSLayoutRelation.Equal,
        toItem: self.view,
        attribute: NSLayoutAttribute.Width,
        multiplier: 1,
        constant: 100)
self.view.addConstraint(constraintButtonPlayWidth)

But the button gets stretched too much; probably because toItem: self.view . I tried modifying the constant of the constraint, but that didn't change anything.

How do I set up correctly this constraint so it actually has a width of 100?

Answer 1

You were close. The constraint only should have a single item since it is not relative to another item.

constraintButtonPlayWidth = NSLayoutConstraint (item: buttonPlay,
    attribute: NSLayoutAttribute.Width,
    relatedBy: NSLayoutRelation.Equal,
    toItem: nil,
    attribute: NSLayoutAttribute.NotAnAttribute,
    multiplier: 1,
    constant: 100)
self.view.addConstraint(constraintButtonPlayWidth)