Swift應用程序遷移問題

Question

我正在將我的應用程序重寫爲Swift，並且目前爲止一切正常。但最近我試圖翻譯UICollectionViewFlowLayout子類，並遇到一些問題。我無法理解如何翻譯這個類的layoutAttributesForElementsInRect方法......我只是得到了太多的錯誤。這個班的問題是，這是我沒有寫的單一的。我從互聯網下載了這個課程，所以我不明白它背後的邏輯。誰能幫我？這裏是完整的類，但我只需要layoutAttributesForElementsInRect方法，因爲我已經成功翻譯了第二個（layoutAttributesForItemAtIndexPath）方法。哦，是的！佈局基本上左對齊相應集合視圖中的每個單元格！感謝您的建議！

#import "IYAlignLeftLayout.h" 

const NSInteger kMaxCellSpacing = 30; 

@implementation IYAlignLeftLayout 

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect { 
    NSArray* attributesToReturn = [super layoutAttributesForElementsInRect:rect]; 
    for (UICollectionViewLayoutAttributes* attributes in attributesToReturn) { 
    if (nil == attributes.representedElementKind) { 
     NSIndexPath* indexPath = attributes.indexPath; 
     attributes.frame = [self layoutAttributesForItemAtIndexPath:indexPath].frame; 
    } 
    } 
    return attributesToReturn; 
} 

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath  *)indexPath { 
    UICollectionViewLayoutAttributes* currentItemAttributes = 
    [super layoutAttributesForItemAtIndexPath:indexPath]; 

    UIEdgeInsets sectionInset = UIEdgeInsetsMake(50, 20, 50, 20); 

    if (indexPath.item == 0) { // first item of section 
    CGRect frame = currentItemAttributes.frame; 
    frame.origin.x = sectionInset.left; // first item of the section should always be  left aligned 
    currentItemAttributes.frame = frame; 

    return currentItemAttributes; 
    } 

    NSIndexPath* previousIndexPath = [NSIndexPath indexPathForItem:indexPath.item-1 inSection:indexPath.section]; 
    CGRect previousFrame = [self  layoutAttributesForItemAtIndexPath:previousIndexPath].frame; 
    CGFloat previousFrameRightPoint = previousFrame.origin.x + previousFrame.size.width + kMaxCellSpacing; 

    CGRect currentFrame = currentItemAttributes.frame; 
    CGRect strecthedCurrentFrame = CGRectMake(0, 
              currentFrame.origin.y, 
              self.collectionView.frame.size.width, 
              currentFrame.size.height); 

    if (!CGRectIntersectsRect(previousFrame, strecthedCurrentFrame)) { // if current item is the first item on the line 
    // the approach here is to take the current frame, left align it to the edge of the view 
    // then stretch it the width of the collection view, if it intersects with the previous frame then that means it 
    // is on the same line, otherwise it is on it's own new line 
    CGRect frame = currentItemAttributes.frame; 
    frame.origin.x = sectionInset.left; // first item on the line should always be left aligned 
    currentItemAttributes.frame = frame; 
    return currentItemAttributes; 
    } 

    CGRect frame = currentItemAttributes.frame; 
    frame.origin.x = previousFrameRightPoint; 
    currentItemAttributes.frame = frame; 
    return currentItemAttributes; 
} 

@end 

Answer 1

試試看看這個代碼。

override func layoutAttributesForElementsInRect(rect: CGRect) -> AnyObject[]! 
    { 
    var attributesToReturn:UICollectionViewLayoutAttributes[] = super.layoutAttributesForElementsInRect(rect) as UICollectionViewLayoutAttributes[] 

    for attributes in attributesToReturn { 

     if let elemedKind = attributes.representedElementKind { 
      var indexPath: NSIndexPath = attributes.indexPath; 
      attributes.frame = self.layoutAttributesForItemAtIndexPath(indexPath).frame 
     } 
    } 
    return attributesToReturn; 
    } 

Answer 2

這裏的代碼;）

override func layoutAttributesForElementsInRect(rect: CGRect) -> [AnyObject]? { 

    var attributesToReturn: [UICollectionViewLayoutAttributes] = super.layoutAttributesForElementsInRect(rect) as [UICollectionViewLayoutAttributes] 

    for (index, attributes) in enumerate(attributesToReturn) { 

     if attributes.representedElementKind != nil { 

      var indexPath: NSIndexPath = attributes.indexPath 
      attributes.frame = layoutAttributesForItemAtIndexPath(indexPath).frame 
     } 
    } 
    return attributesToReturn 
} 

override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes! { 

//  let kMaxCellSpacing: CGFloat = 30.0 

    let currentItemAttributes: UICollectionViewLayoutAttributes = super.layoutAttributesForItemAtIndexPath(indexPath) 

    let sectionInset: UIEdgeInsets = UIEdgeInsetsMake(50.0, 20.0, 50.0, 20.0) 

    if indexPath.item == 0 { // first item of section 
     var frame: CGRect = currentItemAttributes.frame 
     frame.origin.x = sectionInset.left // first item of the section should always be left aligned 
     currentItemAttributes.frame = frame 
     return currentItemAttributes 
    } 

    let previousIndexPath: NSIndexPath = NSIndexPath(forItem: indexPath.item - 1, inSection: indexPath.section) 
    let previousFrame: CGRect = layoutAttributesForItemAtIndexPath(previousIndexPath).frame 
    let previousFrameRightPoint: CGFloat = previousFrame.origin.x + previousFrame.size.width/* + kMaxCellSpacing */ 

    let currentFrame: CGRect = currentItemAttributes.frame 
    let strecthedCurrentFrame: CGRect = CGRectMake(
     0.0, 
     currentFrame.origin.y, 
     self.collectionView!.frame.size.width, 
     currentFrame.size.height) 

    if !CGRectIntersectsRect(previousFrame, strecthedCurrentFrame) { // if current item is the first item on the line 
     // the approach here is to take the current frame, left align it to the edge of the view 
     // then stretch it the width of the collection view, if it intersects with the previous frame then that means it 
     // is on the same line, otherwise it is on it's own new line 
     var frame: CGRect = currentItemAttributes.frame 
     frame.origin.x = sectionInset.left // first item on the line should always be left aligned 
     currentItemAttributes.frame = frame 
     return currentItemAttributes 
    } 

    var frame: CGRect = currentItemAttributes.frame 
    frame.origin.x = previousFrameRightPoint 
    currentItemAttributes.frame = frame 
    return currentItemAttributes 
} 

Answer 3

新雨燕3語法是：

override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? { 
    <#code#> 
}