更新约束时如何避免 UICollectionView 中的淡入动画

Question

当更新 UICollectionView 的约束（缩小或放大）时，项目（缩小或放大）带有淡入淡出动画。如何避免这种情况？

// activating constraints:
containerLeft = containerView.leftAnchor.constraint(equalTo: view.leftAnchor)
containerRight = containerView.rightAnchor.constraint(equalTo: view.rightAnchor)
containerTop =  containerView.topAnchor.constraint(equalTo: view.topAnchor)
containerBottom = containerView.bottomAnchor.constraint(equalTo: view.bottomAnchor)

containerLeft.isActive = true
containerRight.isActive = true
containerTop.isActive = true
containerBottom.isActive = true

改变约束的函数：

func setinsetsForContainer(left: CGFloat, right: CGFloat, top:CGFloat, bottom:CGFloat?){
        containerLeft.constant = left
        containerRight.constant = -right
        containerTop.constant = top
        containerBottom.constant = -bottom!
}

动画更新约束：

setinsetsForContainer(left: 20, right: 20, top:100, bottom:100)
UIView.animate(withDuration: 2) {
 self.view.layoutIfNeeded()
}

Answer 1

只需在UICollectionViewFlowLayout中重写此方法

// disable fade animation in cells
    override func initialLayoutAttributesForAppearingItem(at itemIndexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        let attribute = super.initialLayoutAttributesForAppearingItem(at: itemIndexPath)
        attribute?.alpha = 1
        return attribute
    }

    override func finalLayoutAttributesForDisappearingItem(at itemIndexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        let attribute = super.finalLayoutAttributesForDisappearingItem(at: itemIndexPath)
        attribute?.alpha = 1
        return attribute
    }

//    disable fade animation in header/footer
    override func initialLayoutAttributesForAppearingSupplementaryElement(ofKind elementKind: String, at elementIndexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        let attribute = super.initialLayoutAttributesForAppearingSupplementaryElement(ofKind: elementKind, at: elementIndexPath)
        attribute?.alpha = 1
        return attribute
    }

    override func finalLayoutAttributesForDisappearingSupplementaryElement(ofKind elementKind: String, at elementIndexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        let attribute = super.finalLayoutAttributesForDisappearingSupplementaryElement(ofKind: elementKind, at: elementIndexPath)
        attribute?.alpha = 1
        return attribute
    }