Visual constraints not being recognized - ios

Question

I simply want to set constraints which allows the UIWebView to fill the screen. (Screen has a UINavigationbar and a UIToolBar), I've tried following the examples given in the apple documentation but always get a warning and my view doesnt show up. Below is what I've tried.
private func addSubviews(){
navigationController?.setToolbarHidden(false, animated: false)
// webView = UIWebView(frame: CGRect(x: 0, y: 0, width: UIScreen.mainScreen().bounds.width, height: UIScreen.mainScreen().bounds.height))
webView = UIWebView(frame: CGRectZero)
webView.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(webView)
let views = ["myView" : webView]
let formatString = "|-[myView]-|"
let constraints = NSLayoutConstraint.constraintsWithVisualFormat(formatString, options:[] , metrics: nil, views: views)
NSLayoutConstraint.activateConstraints(constraints)
}

Answer 1

Oofh, visual constraints make my head hurt. I never was a fan of the visual language, never made any sense to me. This may be a bit more code but I think it's much easier to read as a developer and far more expressive as to intent.
self.view.addSubview(webView)
self.view.addConstraint(NSLayoutConstraint(item: self.view, attribute: .Left, relatedBy: .Equal, toItem: webView, attribute: .Left, multiplier: 1, constant: 0))
self.view.addConstraint(NSLayoutConstraint(item: self.view, attribute: .Top, relatedBy: .Equal, toItem: webView, attribute: .Top, multiplier: 1, constant: 0))
self.view.addConstraint(NSLayoutConstraint(item: self.view, attribute: .Bottom, relatedBy: .Equal, toItem: webView, attribute: .Bottom, multiplier: 1, constant: 0))
self.view.addConstraint(NSLayoutConstraint(item: self.view, attribute: .Right, relatedBy: .Equal, toItem: webView, attribute: .Right, multiplier: 1, constant: 0))
These constraints pin all edges of a view to the respective edge with a distance of 0.
Then at the end of your constraints, don't forget:
self.view.layoutIfNeeded()
My problem with the visual language is I can't look at it and immediately be clear as to what it does. Here, it's quite explicit. Just for fun, here's a nice function you can use whenever your constant and multiplier is 0:
/**
Adds an edge constraint between the superview and subview with a constant of 0.
- parameter attribute: Layout attribute.
- parameter subview: Subview.
*/
func addEdgeConstraintWithAttribute(attribute: NSLayoutAttribute, withSubview subview: UIView) {
self.addConstraint(NSLayoutConstraint(item: subview, attribute: attribute, relatedBy: .Equal, toItem: self, attribute: attribute, multiplier: 1, constant: 0))
}
Used like:
self.addEdgeConstraint(.Top, withSubview: webView)
where the function is an extension on UIView

Answer 2

Im my opinion, your view didn't show up because you didn't set up enough constraints for it.
Basically, with a view, you should add constraints to let it know at least the position and the size. In some cases, you dont need to setup size constraints because that view has intrinsic content size like UILabel, UIButton
Back to your example, you should add constraints like this:
private func addSubviews(){
navigationController?.setToolbarHidden(false, animated: false)
// webView = UIWebView(frame: CGRect(x: 0, y: 0, width: UIScreen.mainScreen().bounds.width, height: UIScreen.mainScreen().bounds.height))
let webView = UIWebView(frame: CGRectZero)
webView.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(webView)
let views = ["myView" : webView]
self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-[myView]-|", options:[] , metrics: nil, views: views))
self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-[myView]-|", options:[] , metrics: nil, views: views))
}
H in H:|-[myView]-| stands for horizontal.
V in V:|-[myView]-| stands for vertical.