Tianhao SHI Tianhao SHI - 5 months ago 43
Swift Question

Swift add constraint to superview programmatically

I would like to add some simple constraint but always get error like this:

Terminating app due to uncaught exception 'NSGenericException', reason: 'Unable to install constraint on view. Does the constraint reference something from outside the subtree of the view? That's illegal.


My idea is adding a picker view into a tableview. When the user click on table item this picker view will show. Here is my code:

class InscriptionTableViewController: UITableViewController, UIPickerViewDelegate, UIPickerViewDataSource {

var pickView:UIPickerView!

override func viewDidLoad() {
pickView = UIPickerView()
pickView.delegate = self
pickView.dataSource = self
pickView.hidden = true
pickView.backgroundColor = UIColor.whiteColor()
self.view.addSubview(pickView)

let topContrain = NSLayoutConstraint(
item: pickView,
attribute: NSLayoutAttribute.Top,
relatedBy: NSLayoutRelation.Equal,
toItem: self.view,
attribute: NSLayoutAttribute.Top,
multiplier: 1,
constant: 0)
let bottomContrain = NSLayoutConstraint(
item: pickView,
attribute: NSLayoutAttribute.Bottom,
relatedBy: NSLayoutRelation.Equal,
toItem: self.view,
attribute: NSLayoutAttribute.Bottom,
multiplier: 1,
constant: 0)
pickView.addConstraint(topContrain)
pickView.addConstraint(bottomContrain)
}
}

Answer
self.view.addConstraint(topContrain)
self.view.addConstraint(bottomContrain)