Swift 3 - Constrain Button Width - swift

Question

I am wanting to create a simple bar at the top of my view, with two buttons side by side, taking up 50% each.
I have created the bar like so:
let topTabView = UIView()
topTabView.backgroundColor = UIColor.red
topTabView.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(topTabView)
topTabView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
topTabView.topAnchor.constraint(equalTo: topLayoutGuide.bottomAnchor).isActive = true
topTabView.heightAnchor.constraint(equalToConstant: 60).isActive = true
topTabView.widthAnchor.constraint(equalTo: view.widthAnchor).isActive = true
And this works.
I then add my two buttons, and I get all the constraints right, except I'm not sure how to get the width anchor to work, so that each button takes up 50% of the view.
let filterButton = UIButton()
filterButton.backgroundColor = UIColor.red
filterButton.setTitle("Filter", for: .normal)
filterButton.translatesAutoresizingMaskIntoConstraints = false
topTabView.addSubview(filterButton)
filterButton.leftAnchor.constraint(equalTo: topTabView.leftAnchor).isActive = true
filterButton.centerYAnchor.constraint(equalTo: topTabView.centerYAnchor).isActive = true
filterButton.heightAnchor.constraint(equalTo: topTabView.heightAnchor).isActive = true
// NOT SURE ABOUT THIS ONE
filterButton.widthAnchor.constraint(equalToConstant: 200).isActive = true
let mapButton = UIButton()
mapButton.backgroundColor = UIColor.red
mapButton.setTitle("Map", for: .normal)
mapButton.translatesAutoresizingMaskIntoConstraints = false
topTabView.addSubview(mapButton)
mapButton.rightAnchor.constraint(equalTo: topTabView.rightAnchor).isActive = true
mapButton.centerYAnchor.constraint(equalTo: topTabView.centerYAnchor).isActive = true
mapButton.heightAnchor.constraint(equalTo: topTabView.heightAnchor).isActive = true
// NOT SURE ABOUT THIS ONE
mapButton.widthAnchor.constraint(equalToConstant: 200).isActive = true
I tried something like this but it didn't work:
mapButton.widthAnchor.constraint(equalToConstant: toTabView.frame.width / 2.0).isActive = true
Any help would be amazing!

Answer 1

so that each button takes up 50% of the view
That is what the multiplier is for. You aren't using it. Use it!
So, you want a constraint where a button's width is the same as the superview's width except with a 0.5 value for its multiplier.
Example:
let b1 = UIButton()
b1.translatesAutoresizingMaskIntoConstraints = false
b1.backgroundColor = .green
b1.setTitle("Button1", for: .normal)
b1.setTitleColor(.black, for: .normal)
let b2 = UIButton()
b2.translatesAutoresizingMaskIntoConstraints = false
b2.backgroundColor = .yellow
b2.setTitle("Button2", for: .normal)
b2.setTitleColor(.black, for: .normal)
self.view.addSubview(b1)
self.view.addSubview(b2)
NSLayoutConstraint.activate([
b1.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 50),
b2.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 50),
b1.leadingAnchor.constraint(equalTo:self.view.leadingAnchor),
b2.leadingAnchor.constraint(equalTo:b1.trailingAnchor),
b1.widthAnchor.constraint(equalTo: self.view.widthAnchor, multiplier: 0.5),
b2.widthAnchor.constraint(equalTo: self.view.widthAnchor, multiplier: 0.5),
])
Result: