How to Create layout constraints programmatically

Question

I am displaying a view in the bottom of the universal application and adding this view dynamically in my view. I want to show this view in bottom every time like iAd. in bot

Answer 1

Extending @Alex Shubin solution in Swift 4, I do the following:

Sometimes, I need to add a variable number of constraints, in this case 3, because the height will be calculated latter.

keyboard.addConstaints(top: nil, right: 0.0, bottom: 0.0, left: 0.0, width: nil, height: nil)

You have to be careful adding all required, and making sure you don't have any conflicting constraints.

extension UIView {
    func addConstaints(top: CGFloat?, right: CGFloat?, bottom: CGFloat?, left: CGFloat?, width: CGFloat?, height: CGFloat?) {
        translatesAutoresizingMaskIntoConstraints = false
        if top != nil { self.addConstaint(top: top!) }
        if right != nil { self.addConstaint(right: right!) }
        // Add lines for bottom, left, width an heigh
        // ...
    }
    func addConstaint(top offset: CGFloat) {
        guard superview != nil else { return }
        topAnchor.constraint(equalTo: superview!.topAnchor, constant: offset).isActive = true
    }
}

To verify that all views were laid-out correctly, you can inspect the .constraints property of the superView or you can check the frame in:

override func viewDidLayoutSubviews() {
    print(keyboard.frame)
}