用户交互后UIView消失

Question

whenever I click a textfield inside the view, then click the other text field, the view disappears. Strange... Can anyone help?

I animate the view using facebook pop. Here is my animation engine code: import UIKit import pop

class AnimationEngine {

    class var offScreenRightPosition: CGPoint {
        return CGPoint(x: UIScreen.main.bounds.width + 250,y: UIScreen.main.bounds.midY - 75)
    }

    class var offScreenLeftPosition: CGPoint{
        return CGPoint(x: -UIScreen.main.bounds.width,y: UIScreen.main.bounds.midY - 75)
    }

    class var offScreenTopPosition: CGPoint{
        return CGPoint(x: UIScreen.main.bounds.midX,y: -UIScreen.main.bounds.midY)
    }

    class var screenCenterPosition: CGPoint {
        return CGPoint(x: UIScreen.main.bounds.midX, y: UIScreen.main.bounds.midY - 75)
    }

    let ANIM_DELAY : Int = 1
    var originalConstants = [CGFloat]()
    var constraints: [NSLayoutConstraint]!

    init(constraints: [NSLayoutConstraint]) {

        for con in constraints {
            originalConstants.append(con.constant)
            con.constant = AnimationEngine.offScreenRightPosition.x
        }

        self.constraints = constraints
    }

    func animateOnScreen(_ delay: Int) {

        let time = DispatchTime.now() + Double(Int64(Double(delay) * Double(NSEC_PER_SEC))) / Double(NSEC_PER_SEC)

        DispatchQueue.main.asyncAfter(deadline: time) {

            var index = 0
            repeat {
                let moveAnim = POPSpringAnimation(propertyNamed: kPOPLayoutConstraintConstant)
                moveAnim?.toValue = self.originalConstants[index]
                moveAnim?.springBounciness = 8
                moveAnim?.springSpeed = 8

                if (index < 0) {
                    moveAnim?.dynamicsFriction += 10 + CGFloat(index)
                }

                let con = self.constraints[index]
                con.pop_add(moveAnim, forKey: "moveOnScreen")

                index += 1

            } while (index < self.constraints.count)
        }

    }

    class func animateToPosisition(_ view: UIView, position: CGPoint, completion: ((POPAnimation?, Bool) -> Void)!) {
        let moveAnim = POPSpringAnimation(propertyNamed: kPOPLayerPosition)
        moveAnim?.toValue = NSValue(cgPoint: position)
        moveAnim?.springBounciness = 8
        moveAnim?.springSpeed = 8
        moveAnim?.completionBlock = completion
        view.pop_add(moveAnim, forKey: "moveToPosition")
    }
}

Then here is my viewcontroller code where the view is inside in:

import UIKit
import pop


class LoginVC: UIViewController, UITextFieldDelegate {

    override var prefersStatusBarHidden: Bool {
        return true
    }

    @IBOutlet weak var emailLoginVCViewConstraint: NSLayoutConstraint!
    @IBOutlet weak var emailLoginVCView: MaterialView!
    @IBOutlet weak var emailAddressTextField: TextFieldExtension!
    @IBOutlet weak var passwordTextField: TextFieldExtension!

    var animEngine : AnimationEngine!

    override func viewDidAppear(_ animated: Bool) {
        self.emailLoginVCView.isUserInteractionEnabled = true
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        self.view.bringSubview(toFront: emailAddressTextField)
        self.animEngine = AnimationEngine(constraints: [emailLoginVCViewConstraint])
        self.emailAddressTextField.delegate = self
        self.passwordTextField.delegate = self
        emailAddressTextField.allowsEditingTextAttributes = false
    }


    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        if (textField === emailAddressTextField) {
            passwordTextField.becomeFirstResponder()
        } else if (textField === passwordTextField) {
            passwordTextField.resignFirstResponder()
        } else {
            // etc
        }

        return true
    }

    @IBAction func emailTapped(_ sender: AnyObject) {
        AnimationEngine.animateToPosisition(emailLoginVCView, position: AnimationEngine.screenCenterPosition, completion: { (POPAnimation, Bool)
            in
        })
    }

    @IBAction func exitTapped(_ sender: AnyObject) {
        AnimationEngine.animateToPosisition(emailLoginVCView, position: AnimationEngine.offScreenRightPosition, completion: { (POPAnimation, Bool)
            in
        })
    }

}

Last here is my hierchy and options: (my view's name is emailLoginVCView). Also when I was debugging when I clicked another textfield I set a breakpoint so I got this info: enter image description here

Answer 1

1. I have a constraint that binds the center of the login view with the center of the main screen

2. when I create the AnimationEngine,I pass it that constraint, and it sets its constant to be the offScreenRightPosition.x

3. when I bring up the email login sheet, I'm not changing the constant of the constraint; I'm just changing the position of the view

4. which means that autolayout thinks it's supposed to still be offscreen

5. when the second textfield becomes active, that's somehow triggering auto-layout to re-evaluate the constraints, and it sees that the login view's position doesn't match what the constraint says it should be so....

6. Autolayout moves it offscreen

So if I add this in emailTapped(_:) , the problem goes away :)

@IBAction func emailTapped(_ sender: AnyObject) { AnimationEngine.animateToPosisition(emailLoginVCView, position: AnimationEngine.screenCenterPosition, completion: { (POPAnimation, Bool) in self.emailLoginVCViewConstraint.constant = 0 }) }