Right upper constraint format

Question

I am struggling with adding one button from code to the right corner of the view. Could someone explain me how can i do this without setting the left constraint ? This would be the left upper V:|-10-[v0], H:|-10-[v0] what would be inversion of it ? I was trying with this : V:[v0]-10-|, H:[v0]-0-| but it does not work like i thought

Thanks in advance!

Answer 1

Based on the comments, I'd like to provide two answers on how to place a UIButton on the top right.

VFL:

Your vertical pin is for the bottom right, not the top. Instead of V:[v0]-10-|, where the "pipe" character (that designates the bounds of the screen) is at the end, place it at the beginning - |-10-[v0].

Provided you've given the button some sort of height/width - which I think you have as the code for "top left" works - this should fix things.

Anchors

Introduced in iOS9, layout anchors (along with layout guides) are a third way to code auto layout. Like NSLayoutConstraints, this is less "visual" than VFL. But unlike NSLayoutConstraints it's less verbose - thus more "Swiftier" IMHO.

To pin a UIButton to the top left, you still need to give auto layout four things - height, width, and X/Y positions. In the following I'm assuming the superview of v0 is called view, like the root view of a UIViewController.

// declare your button
let v0 = UIButton()

override func viewDidLoad() {
    super.viewDidLoad()

    // remember, you ALWAYS need to turn of the auto resize mask!
    v0.translatesAutoresizingMaskIntoConstraints = false

    view.addSubview(v0)

    // create a square button
    v0.widthAnchor.constraint(equalToConstant: 100.0).isActive = true        
    v0.heightAnchor.constraint(equalToConstant: 100.0).isActive = true

    // pin the button 10 points from the left side of the view
    v0.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 10).isActive = true        

    // here's how you would pin the button 10 points from the right side of the view
    // note the use of a negative here!
    // v0.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -10).isActive = true        

    // pin the button 10 points from the top of the view
    v0.topAnchor.constraint(equalTo: view.topAnchor, constant: 10).isActive = true

}

Like NSLayoutConstraints, layout anchors have constants and multipliers, which you may change if you declare a name for the constraint.

You may combine NSLayoutConstraints with NSLayoutGuides for some nice "adaptive layouts". These guides act like "spacer/invisible" UIViews except for the overhead - they aren't views. You can get a set of Apple "standard" margins (UIView.layoutMarginsGuide), or you can create a set of equally size dynamic guides to space things out equally.

Here's two blogs about layout anchors and layout guides. The examples are written in Swift 2 but there's no syntax changes for Swift 3.