UIView 在用户交互后消失

Question

每当我单击视图内的文本字段，然后单击另一个文本字段时，视图就会消失。奇怪...有人可以帮忙吗？

我使用 facebook pop 为视图设置动画。这是我的动画引擎代码： 导入 UIKit 进口流行音乐

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")
    }
}

然后这是我的视图控制器代码，其中视图位于：

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
        })
    }

}

最后是我的层次结构和选项：（我的视图名称是 emailLoginVCView）。此外，当我单击另一个文本字段进行调试时，我设置了一个断点，因此我得到了以下信息：enter image description here

Answer 1

1. 我有一个约束，将登录视图的中心与主屏幕的中心绑定

2. 当我创建 AnimationEngine 时，我将那个约束传递给它，并将其 constant 设置为 offScreenRightPosition.x

3. 当我打开电子邮件登录表时，我并没有更改约束的常量；我只是在改变视图的位置

4. 这意味着自动布局认为它应该仍然在屏幕外

5. 当第二个文本字段变为活动状态时，这会以某种方式触发自动布局以重新评估约束，并且它会看到登录视图的位置与约束所说的不匹配......

6. 自动布局将其移出屏幕

所以如果我在emailTapped(_:) 中添加这个，问题就会消失 :)

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