swift - 一旦 UIView 出现在屏幕上就开始动画

Question

我有一个自定义 UIView，我想在用户点击按钮后覆盖屏幕。它有点模拟自定义 View 。自定义 UIView 中有一个子 UIView，它应该从底部(首先隐藏)到其正常位置(在底部可见)进行动画处理。我遇到的问题是，layoutSubviews 似乎不是开始制作动画的好地方。正确的地方在哪里？类似于 viewDidAppear 但适用于 UIViews。

在 UIViewController 中:

let rect: CGRect = CGRectMake(0, 0, view.bounds.size.width, view.bounds.size.height)
let alertView = AlertView(frame: rect)
view.addSubview(alertView)

在 AlertView 中:

import UIKit

class AlertView: UIView {

let nibName = "AlertView"
let animationDuration = 0.5

var view: UIView!

@IBOutlet weak var notificationView: UIView!
@IBOutlet weak var notificationBottomConstraint: NSLayoutConstraint!

override init(frame: CGRect) {
    super.init(frame: frame)
    viewSetup()
}

required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
    viewSetup()
}

override func didAddSubview(subview: UIView) {
    super.didAddSubview(subview)
}

func viewSetup() {
    view = loadViewFromNib()
    view.frame = bounds
    view.autoresizingMask = [UIViewAutoresizing.FlexibleWidth, UIViewAutoresizing.FlexibleHeight]

    // move the notification view offscreen
    notificationBottomConstraint.constant = -notificationView.frame.size.height

    addSubview(view)
}

func loadViewFromNib() -> UIView {
    let bundle = NSBundle(forClass: self.dynamicType)
    let nib = UINib(nibName: nibName, bundle: bundle)

    return nib.instantiateWithOwner(self, options: nil)[0] as! UIView
}

override func layoutSubviews() {
    super.layoutSubviews()
    print("layoutSubviews")

    animate()
}

func animate() {
    // move the notification up 
    self.notificationBottomConstraint.constant = 0

    UIView.animateWithDuration(animationDuration) { () -> Void in
        self.view.setNeedsDisplay()
    }
}

}

Answer 1

我建议您从以下方法之一调用 animate() 函数:

• willMoveToSuperview:
• didMoveToSuperview

UIView 的这些方法根据需要跟踪 View 层次结构中当前 View 的移动。

引用: UIView class