How to change height of UIView that already has height anchor?

问题

If I have this for a child view controller:

autoCompleteViewController.view.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            autoCompleteViewController.view.topAnchor.constraint(equalTo: view.topAnchor, constant: 0),
            autoCompleteViewController.view.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0),
            autoCompleteViewController.view.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0),
            autoCompleteViewController.view.bottomAnchor.constraint(equalTo: googleMapViewController.view.topAnchor, constant: 0),
            autoCompleteViewController.view.heightAnchor.constraint(equalToConstant: 44.0)
        ])

how can I change its height and update heightAnchor? I've tried this:

autoCompleteViewController
            .view
            .heightAnchor
            .constraint(equalToConstant: initialHeightAutoCompleteViewController + CGFloat(numberOfSuggestions * 45))
            .isActive = true

but with no luck. I also tried to add layoutIfNeeded() and some other similar methods but it didn't work. How can I update view height with anchors? Thanks for your answers.

回答1:

Additionally to @Mukesh answer is simply updating the constraint:

var heightAnchor:NSLayoutConstraint!

override func viewDidLoad() {
    super.viewDidLoad()
    heightAnchor = autoCompleteViewController.view.heightAnchor.constraint(equalToConstant:44.0)
    heightAnchor.isActive = true
}

func changeMyHeight(numberOfSuggestions: Int) {
    heightAnchor.constant = 44.0 + CGFloat(numberOfSuggestions * 45)
}

Notes:

You cannot fully declare this variable at the class level, as autoCompleteViewController.view is not yet instantiated.
You cannot set up the constraint and set isActive = true at the same time. I've always gotten a build error.

回答2:

First you have disable the previous constraint and activate another

For example

let heightAnchor_one = autoCompleteViewController.view.heightAnchor.constraint(equalToConstant: x)

let heightAnchor_two = autoCompleteViewController.view.heightAnchor.constraint(equalToConstant: y)

heightAnchor_one.isActive = true

heightAnchor_two.isActive = false

then whichever constraint you need activate that and disable the other.

回答3:

If you don't want to keep a reference to the height anchor, here is an alternative...

   myVC.view.constraints.forEach { (constraint) in
        if constraint.firstAttribute == .height
        {
            constraint.constant = newHeight
        }
    }

Good luck!

回答4:

You can do something like this:

class ViewController: UIViewController {

    var constantValue: CGFloat = 44

    let childView: UIView = {
        let view = UIView()
        view.backgroundColor = .red
        return view
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(childView)

        childView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            childView.topAnchor.constraint(equalTo: view.topAnchor, constant: 0),
            childView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0),
            childView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0),
            childView.heightAnchor.constraint(equalToConstant: constantValue)
            ])

    }

    @IBAction func changeHeight(_ sender: UIButton) {

        constantValue = 100

        UIView.animate(withDuration: 0.5, animations: {

            if let constraint = (self.childView.constraints.filter{$0.firstAttribute == .height}.first) {

                constraint.constant = self.constantValue
            }

            self.view.layoutIfNeeded()
        })
    }

}

回答5:

I've fixed it by implementing it like this:

autoCompleteViewControllerHeight = NSLayoutConstraint( item: autoCompleteViewController.view, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .height, multiplier: 1.0, constant: 44.0) guard let autoCompleteViewControllerHeight = autoCompleteViewControllerHeight else { return } autoCompleteViewControllerHeight.isActive = true

and then where it should be changed I added:

let newHeight = calculateNewHeight() heightConstraintAutoCompleteViewController.constant = newHeight

It works like a charm.

来源：https://stackoverflow.com/questions/45144640/how-to-change-height-of-uiview-that-already-has-height-anchor

标签

ios

swift

nslayoutconstraint