Swift: animateWithDuration行为

Question

我已经制作了简单的文本和按钮动画，从屏幕之外到屏幕中间，但它没有。它从屏幕上移动到屏幕外。基本上，动画是反转的。

我已经看到，其他应用程序的工作方式，我不会使用相同的代码，所以我不知道哪里出了问题。:(

代码如下：

import UIKit

class ViewController: UIViewController {

@IBOutlet weak var welcomeText: UILabel!
@IBOutlet weak var worksText: UILabel!
@IBOutlet weak var loginButton: UIButton!
@IBOutlet weak var signUp: UIButton!
@IBOutlet weak var socialLog: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()

}

override func viewWillAppear(animated: Bool) {

    welcomeText.alpha = 0.0
    worksText.alpha = 0.0
    loginButton.alpha = 0.0
    signUp.alpha = 0.0
    socialLog.alpha = 0.0

    welcomeText.center.x -= view.bounds.width
    worksText.center.x -= view.bounds.width
    socialLog.center.x -= view.bounds.width
    signUp.center.x -= view.bounds.width
}

override func viewDidAppear(animated: Bool) {

    self.welcomeText.fadeIn()
    UIView.animateWithDuration(0.7, delay: 0.1, options: .CurveEaseOut, animations: {
        self.welcomeText.center.x += self.view.bounds.width
        self.view.layoutIfNeeded()
        }, completion: nil)

    self.worksText.fadeIn()
    UIView.animateWithDuration(0.7, delay: 0.5, options: .CurveEaseOut, animations: {
        self.worksText.center.x += self.view.bounds.width
        self.view.layoutIfNeeded()
        }, completion: nil)

    self.socialLog.fadeIn()
    UIView.animateWithDuration(0.7, delay: 0.3, options: .CurveEaseOut, animations: {
        self.socialLog.center.x += self.view.bounds.width
        self.view.layoutIfNeeded()
        }, completion: nil)

    self.signUp.fadeIn()
    UIView.animateWithDuration(0.7, delay: 0.7, options: .CurveEaseOut, animations: {
        self.signUp.center.x += self.view.bounds.width
        self.signUp.alpha = 0.5
        self.view.layoutIfNeeded()
        }, completion: nil)
}
}

extension UIView {
func fadeIn(duration: NSTimeInterval = 0.5, delay: NSTimeInterval = 0.0, completion: ((Bool) -> Void) = {(finished: Bool) -> Void in}) {
    UIView.animateWithDuration(duration, delay: delay, options: UIViewAnimationOptions.CurveEaseIn, animations: {
        self.alpha = 1.0
        }, completion: completion)  }

func fadeOut(duration: NSTimeInterval = 0.5, delay: NSTimeInterval = 0.0, completion: (Bool) -> Void = {(finished: Bool) -> Void in}) {
    UIView.animateWithDuration(duration, delay: delay, options: UIViewAnimationOptions.CurveEaseIn, animations: {
        self.alpha = 0.0
        }, completion: completion)
}
}

Answer 1

调试时需要有关视图开始位置的信息。但是，我强烈建议不要对这样的动画使用+=或-=。正如您所经历的，它的行为是不可预测的，因为它完全依赖于当前状态。

相反，您可以在viewWillAppear：*view*.center.x = -(*view*.frame.width / 2)和viewDidAppear: view.center.x =中执行此操作

此外，更新的方法是使用和动画约束，而不是帧。