Changing an Autolayout-constrained UIView's frame at runtime in Swift

问题

For example, I use this code to change the frame position of a UIView called Propo:

        self.Propo.frame.origin.x -= self.view.frame.width

(Propo has constraints in Storyboard)

But When the app view disappears and reappears, the UIView resets itself to its original position. How can I do to resolve it? I want the UIView to keep its position when I change it programmatically.

I've tried updateViewConstraints() by anything else append...

回答1:

Constraints and manual frame manipulation are directly in conflict. You have to choose one or the other. You should instead "promote" the constraint you wish to change by Ctrl-dragging it to your view controller as an @IBOutlet in Storyboard. Then, you can manipulate its constant:

class MyViewController: UIViewController {
    @IBOutlet weak var myPropoLeftEdgeConstraint: NSLayoutConstraint!

    @IBAction doChangePropo(sender: AnyObject) {
        myPropoLeftEdgeConstraint.constant -= view.frame.width
        view.layoutIfNeeded()
    }
}

This is already covered in Objective C in many places, so just do a search on programmatically changing an NSLayoutConstraint in code if you can read those examples.

How to edit constraint in code

(Edit to make more applicable: generally constraints should be animated for a clean user experience. Otherwise the eye is confused.)

You can easily animate the constraint adjustment by wrapping view.layoutIfneeded in a UIView.animateWithDuration(duration) { ... } block.

来源：https://stackoverflow.com/questions/39193445/changing-an-autolayout-constrained-uiviews-frame-at-runtime-in-swift

标签

ios

swift

uiview

autolayout