clear constraints when using NSLayoutAnchor

Question

I'm new in creating views without interface builder . I'm using NSLayoutAnchors to create views!

when I'm using some view that created in viewcontroller like this :

let borderView:UIView = {

    let view = UIView()
    view.translatesAutoresizingMaskIntoConstraints = false
    view.backgroundColor = UIColor.lightGray
    view.isUserInteractionEnabled = false
    view.alpha = 0.5
    return view

}()

then i use this view to border sth in view like this :

view.addSubview(borderView)
borderView.bottomAnchor.constraint(equalTo: headerView.bottomAnchor).isActive = true
borderView.leftAnchor.constraint(equalTo: headerView.leftAnchor).isActive = true
borderView.rightAnchor.constraint(equalTo: headerView.rightAnchor).isActive = true
borderView.heightAnchor.constraint(equalToConstant: 1).isActive = true

then in another view i try this :

    informationView.addSubview(borderView)

    borderView.topAnchor.constraint(equalTo: informationView.topAnchor).isActive = true
    borderView.leftAnchor.constraint(equalTo: informationView.leftAnchor).isActive = true
    borderView.rightAnchor.constraint(equalTo: informationView.rightAnchor).isActive = true
    borderView.heightAnchor.constraint(equalToConstant: 1).isActive = true

but looks like this view has it's previous constraints end show constraints error !

how can I remove borderView constraints before reusing it ?

Possible duplicate of Remove all constraints affecting a UIView — dirtydanee
– dirtydanee, Commented Apr 12, 2017 at 14:17
It's not really a duplicate because the answer is not to reuse the view (removing constraints wouldn't help in this case) — Lou Franco
– Lou Franco, Commented Apr 12, 2017 at 14:25

Lou Franco · Accepted Answer · 2017-04-12 14:18:57Z

7

You can't reuse views. Each view can only be in the view hierarchy one time. You need to make a new bordered view object for each view you want to use it with.

To answer the question, you can remove constraints from a view with view.removeConstraints(view.constraints)

answered Apr 12, 2017 at 14:18

Lou Franco

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2 Comments

shaibow Over a year ago

what is a best practice to make some border view using this method ?

Lou Franco Over a year ago

Something like: (1) don't have a property for it (2) make a func that takes a view, makes a new border view, sets constraints and adds it as a sub to the passed in view, so you just do addBorderView(to: view)

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