NSCollectionViewFlowLayout生成一个布局,其右边距上的项目对齐,或者,如果容器只有一个项目的宽度,则居中项目。我期待一个对齐选项,例如代表,但我没有在文档中找到任何东西。是否需要继承NSCollectionViewFlowLayout才能实现此目的?
这是一个产生左对齐流布局的子类:
class LeftFlowLayout: NSCollectionViewFlowLayout {
override func layoutAttributesForElementsInRect(rect: CGRect) -> [NSCollectionViewLayoutAttributes] {
let defaultAttributes = super.layoutAttributesForElementsInRect(rect)
if defaultAttributes.isEmpty {
// we rely on 0th element being present,
// bail if missing (when there's no work to do anyway)
return defaultAttributes
}
var leftAlignedAttributes = [NSCollectionViewLayoutAttributes]()
var xCursor = self.sectionInset.left // left margin
// if/when there is a new row, we want to start at left margin
// the default FlowLayout will sometimes centre items,
// i.e. new rows do not always start at the left edge
var lastYPosition = defaultAttributes[0].frame.origin.y
for attributes in defaultAttributes {
if attributes.frame.origin.y > lastYPosition {
// we have changed line
xCursor = self.sectionInset.left
lastYPosition = attributes.frame.origin.y
}
attributes.frame.origin.x = xCursor
// by using the minimumInterimitemSpacing we no we'll never go
// beyond the right margin, so no further checks are required
xCursor += attributes.frame.size.width + minimumInteritemSpacing
leftAlignedAttributes.append(attributes)
}
return leftAlignedAttributes
}
}
当collectionViewItems
身高不均匀时,@ Obliquely的答案失败了。这是他们的代码修改,以处理Swift 4.2中的非统一大小的项目:
class CollectionViewLeftFlowLayout: NSCollectionViewFlowLayout
{
override func layoutAttributesForElements(in rect: CGRect) -> [NSCollectionViewLayoutAttributes]
{
let defaultAttributes = super.layoutAttributesForElements(in: rect)
if defaultAttributes.isEmpty {
return defaultAttributes
}
var leftAlignedAttributes = [NSCollectionViewLayoutAttributes]()
var xCursor = self.sectionInset.left // left margin
var lastYPosition = defaultAttributes[0].frame.origin.y // if/when there is a new row, we want to start at left margin
var lastItemHeight = defaultAttributes[0].frame.size.height
for attributes in defaultAttributes
{
// copy() Needed to avoid warning from CollectionView that cached values are mismatched
guard let newAttributes = attributes.copy() as? NSCollectionViewLayoutAttributes else {
continue;
}
if newAttributes.frame.origin.y > (lastYPosition + lastItemHeight)
{
// We have started a new row
xCursor = self.sectionInset.left
lastYPosition = newAttributes.frame.origin.y
}
newAttributes.frame.origin.x = xCursor
xCursor += newAttributes.frame.size.width + minimumInteritemSpacing
lastItemHeight = newAttributes.frame.size.height
leftAlignedAttributes.append(newAttributes)
}
return leftAlignedAttributes
}
}
如果您的商品具有相同的宽度......
在另一个委托方法中,您应该更改NSCollectionViewLayoutAttributes的框架
- (NSCollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
NSCollectionViewLayoutAttributes *attributes = [[super layoutAttributesForItemAtIndexPath:indexPath] copy];
NSRect modifiedFrame = [attributes frame];
modifiedFrame.origin.x = floor(modifiedFrame.origin.x / (modifiedFrame.size.width + [self minimumInteritemSpacing])) * (modifiedFrame.size.width + [self minimumInteritemSpacing]);
[attributes setFrame:modifiedFrame];
return [attributes autorelease];
}
swift 4.2的更短解决方案:
class CollectionViewLeftFlowLayout: NSCollectionViewFlowLayout {
override func layoutAttributesForElements(in rect: NSRect) -> [NSCollectionViewLayoutAttributes] {
let attributes = super.layoutAttributesForElements(in: rect)
if attributes.isEmpty { return attributes }
var leftMargin = sectionInset.left
var lastYPosition = attributes[0].frame.maxY
for itemAttributes in attributes {
if itemAttributes.frame.origin.y > lastYPosition{ // NewLine
leftMargin = sectionInset.left
}
itemAttributes.frame.origin.x = leftMargin
leftMargin += itemAttributes.frame.width + minimumInteritemSpacing
lastYPosition = itemAttributes.frame.maxY
}
return attributes
}
}