Question

我很难在布局中以类似架子的方式实现装饰视图。首先，我想在滚动时生成新的decorationView元素，不要将它们添加到缓存中。但是当我尝试使用最后一个单元格的indexPath生成decorationView时，在删除项目应用程序时，应用程序会立即崩溃。然后，我尝试为装饰视图实现一些缓存，在layoutAttributesForElements(in rect: CGRect)中检查它们，但是应用程序开始做奇怪的想法：如果我尝试删除其中一个未在屏幕上首先显示的项目，应用程序立即崩溃。但是，如果我首先删除这些元素的几个元素，然后开始从最后删除元素，一切都很顺利。如何更好地将这些装饰器添加到我的布局？我现在的代码如下：

class YourFoodFlowLayout: UICollectionViewFlowLayout {
private enum DecorationViewKind: String {
    case shelfView = "ShelfView"
}

private var cashedDecorationView = [UICollectionViewLayoutAttributes]()

override init() {
    super.init()
    self.register(ShelfCollectionReusableView.self, forDecorationViewOfKind: DecorationViewKind.shelfView.rawValue)
}


required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
    self.register(ShelfCollectionReusableView.self, forDecorationViewOfKind: DecorationViewKind.shelfView.rawValue)
}

override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
    guard let atributes = super.layoutAttributesForElements(in: rect) else {
        return nil
    }
    var mutatingAtributes = atributes
    //find max Y position of the cells

    var position = CGRect.zero
    position.size.width = rect.size.width
    position.size.height = 16

    for atribute in mutatingAtributes {
        atribute.zIndex = 1
        if atribute.frame.maxY > position.origin.y {
            position.origin.y = atribute.frame.maxY
            if rect.intersects(position) {
                var atribute: UICollectionViewLayoutAttributes? = nil
                for decorationView in cashedDecorationView {
                    if decorationView.frame == position {
                        atribute = decorationView
                    }
                }
                if let atribute = atribute {
                    mutatingAtributes.append(atribute)
                } else {
                    guard let shelfAtribute = layoutAttributesForDecorationView(ofKind: DecorationViewKind.shelfView.rawValue, at: IndexPath(index: cashedDecorationView.count)) else {
                        continue
                    }
                    shelfAtribute.frame = position
                    cashedDecorationView.append(shelfAtribute)
                    mutatingAtributes.append(shelfAtribute)
                }
            }

        }
    }

    return mutatingAtributes
}

override func prepare() {
    super.prepare()

}

override var collectionViewContentSize: CGSize {
    return CGSize(width: super.collectionViewContentSize.width, height: super.collectionViewContentSize.height + 16)
}

override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
    return super.layoutAttributesForItem(at: indexPath)
}


override func layoutAttributesForDecorationView(ofKind elementKind: String, at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
    switch elementKind {
    case DecorationViewKind.shelfView.rawValue:
        return UICollectionViewLayoutAttributes(forDecorationViewOfKind: elementKind, with: indexPath)
    default:
        print("Unexpected decoration layout element kind")
        return nil
    }
}

}

Answer 1

好的，我找到了两件事：1）$("#my-button").on("click", function() { $("my-form").submit(); });每次滚动时都不会打电话; 2）collectionViewLayout有一些之前使用过的缓存indexPath。即使您尝试重新加载某些数据，也必须先调用layoutAttributesForElements(in rect: CGRect)重新加载这些indexPath。以下内容对我有帮助：

invalidateLayout()

Swift collectionView添加架子装饰器

1 个答案: