ios - 单元格中的 CGAffineTransform 动画不起作用

Question

我在为 CollectionViewCell 内的 UIImageView 设置动画时遇到问题。我已经使用 Auto Layout 设置了 View ，不确定这是否会导致问题。

如果尝试调用 didEndDisplaying 但没有结果。调用单元格动画的正确生命周期函数是什么？

代码:

import UIKit

class ProfileCell: UICollectionViewCell {

    ....

    let backgroundImageView: UIImageView = {
        let iv = UIImageView(frame: .zero)
        iv.contentMode = .scaleAspectFill
        iv.image = UIImage(named: "lustrum2017")
        iv.clipsToBounds = true
        return iv
    }()

    var blurView: UIVisualEffectView = {
        let be = UIBlurEffect(style: .light)
        let vv = UIVisualEffectView(effect: be)
        return vv
    }()

    let profileImageView: UIImageView = {
        let iv = UIImageView()
        iv.image = UIImage(named: "dummy")
        iv.contentMode = .scaleAspectFill
        iv.layer.cornerRadius = 40
        iv.layer.masksToBounds = true
        iv.layer.borderColor = Colors.primaryColor.cgColor
        iv.layer.borderWidth = 1.0
        iv.transform = CGAffineTransform(scaleX: 0.001, y: 0.001)
        return iv
    }()

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

        setupViews()
        animateViews()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    private func animateViews() {

        self.profileImageView.transform = CGAffineTransform(scaleX: 1, y: 1)

        UIView.animate(withDuration: 0.45, animations: { 
            self.layoutIfNeeded()
        }, completion: nil)
    }

    private func setupViews() {
        contentView.addSubview(backgroundImageView)
        contentView.addSubview(blurView)

        contentView.addConstraintsWithFormat("H:|[v0]|", views: backgroundImageView)
        contentView.addConstraintsWithFormat("V:|[v0(150)]", views: backgroundImageView)

        contentView.addConstraintsWithFormat("H:|[v0]|", views: blurView)
        contentView.addConstraintsWithFormat("V:|[v0(150)]", views: blurView)

        blurView.addSubview(profileImageView)
        blurView.addConstraintsWithFormat("H:|-\(frame.width / 2 - 40)-[v0(80)]-\(frame.width / 2 - 40)-|", views: profileImageView)
        blurView.addConstraintsWithFormat("V:|[v0(80)]", views: profileImageView)
    }

    ....

}

Answer 1

您可以尝试在 UIView.animate block 内进行转换，它应该可以工作。如下:

private func animateViews() {

    self.profileImageView.transform = CGAffineTransform.identity
    UIView.animate(withDuration: 0.45, animations: { 
        self.profileImageView.transform = CGAffineTransform(scaleX: 1, y: 1)
        self.layoutIfNeeded()
    }, completion: nil)
}

此外，如果您从 Storyboard/xib 创建单元格而不是通过代码手动注册单元格，awakeFromNib 可能会为您提供所需的结果。

编辑:上面的答案假设您希望动画在单元格首次创建后发生，因为它看起来与您的代码更相似。如果您希望每次单元格出现在屏幕上时都调用它，那么您需要使用 UICollectionViewDelegate 的 collectionView(_:willDisplay:forItemAt:)