Ios UICollectionViewLayout（从Swift转换为Objective-C）

我目前正在学习这个教程（），它创建了一个自定义的UICollectionViewLayout，问题是这个教程是用Swift编写的，但是我正在尝试将它转换为我的项目的Objective-C

将教程复制到Objective-C的第一部分很好，我已经到了这个阶段

但是，在第二部分中，当我们假设创建自定义UICollectionViewLayout时，在情节提要中将CollectionView的布局更改为custom并设置自定义类时，会出现一个空白屏幕

以下是我从Swift到Objective-C的教程中复制的代码：

@implementation TimetableCustomLayout{
    NSMutableArray *cache;
}

-(NSInteger)featuredItemIndex{

CGFloat dragOffset = 180;
    return MAX(0, self.collectionView.contentOffset.y - dragOffset);
}

-(CGFloat)nextItemPercentageOffset{
    CGFloat dragOffset = 180;
    return (self.collectionView.contentOffset.y / dragOffset) - [self    featuredItemIndex];
}

-(CGFloat)width{
    return CGRectGetWidth(self.collectionView.bounds);
}

-(CGFloat)height{
    return CGRectGetHeight(self.collectionView.bounds);
}

-(NSInteger)numberOfItems{
    //Will be replaced with dynamic value later
    return 5;
}


-(CGSize)collectionViewContentSize{

    CGFloat dragOffset = 180;



    return CGSizeMake([self height], [self width]);
}


-(void)prepareLayout{

    [super prepareLayout];
    cache = [[NSMutableArray alloc]initWithObjects:[UICollectionViewLayoutAttributes class], nil];

    self.standardHeight = 100;
    self.featuredHeight = 280;

    CGRect frame = CGRectZero;
    CGFloat y = 0;

    for(int item = 0; item < 5; item ++){
        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:item inSection:0];
        UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];

        attributes.zIndex = item;
        CGFloat height = self.standardHeight;

        if(indexPath.item == [self featuredItemIndex]){
            CGFloat yOffset = self.standardHeight * [self nextItemPercentageOffset];
            y = self.collectionView.contentOffset.y - yOffset;

            height = self.featuredHeight;

    }else if(indexPath.item == ([self featuredItemIndex] + 1) && indexPath.item != [self numberOfItems]){
            CGFloat maxY = y + self.standardHeight;
            height = self.standardHeight + MAX((self.featuredHeight - self.standardHeight) * [self nextItemPercentageOffset], 0);
            y = maxY - height;
    }

        frame = CGRectMake(0, y, [self width], [self height]);
    attributes.frame = frame;
        [cache addObject:attributes];

        y = CGRectGetMaxY(frame);

    }

}

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    [super layoutAttributesForElementsInRect:rect];



    NSMutableArray *layoutAttributes = [[NSMutableArray alloc]initWithObjects:[UICollectionViewLayoutAttributes class], nil];

    NSLog(@"%@", cache);

    for(UICollectionViewLayoutAttributes *attributes in cache){
        if(CGRectIntersectsRect(attributes.frame, rect)){
            [layoutAttributes addObject:attributes];
        }
    }

    return layoutAttributes;

}


-(BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds{
    return true;
}

@end

NSMutableArray *layoutAttributes = [[NSMutableArray alloc]initWithObjects:[UICollectionViewLayoutAttributes class], nil];

目标C：

@implementation TimetableCustomLayout{
    NSMutableArray *cache;
}

-(NSInteger)featuredItemIndex{

CGFloat dragOffset = 180;
    return MAX(0, self.collectionView.contentOffset.y - dragOffset);
}

-(CGFloat)nextItemPercentageOffset{
    CGFloat dragOffset = 180;
    return (self.collectionView.contentOffset.y / dragOffset) - [self    featuredItemIndex];
}

-(CGFloat)width{
    return CGRectGetWidth(self.collectionView.bounds);
}

-(CGFloat)height{
    return CGRectGetHeight(self.collectionView.bounds);
}

-(NSInteger)numberOfItems{
    //Will be replaced with dynamic value later
    return 5;
}


-(CGSize)collectionViewContentSize{

    CGFloat dragOffset = 180;



    return CGSizeMake([self height], [self width]);
}


-(void)prepareLayout{

    [super prepareLayout];
    cache = [[NSMutableArray alloc]initWithObjects:[UICollectionViewLayoutAttributes class], nil];

    self.standardHeight = 100;
    self.featuredHeight = 280;

    CGRect frame = CGRectZero;
    CGFloat y = 0;

    for(int item = 0; item < 5; item ++){
        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:item inSection:0];
        UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];

        attributes.zIndex = item;
        CGFloat height = self.standardHeight;

        if(indexPath.item == [self featuredItemIndex]){
            CGFloat yOffset = self.standardHeight * [self nextItemPercentageOffset];
            y = self.collectionView.contentOffset.y - yOffset;

            height = self.featuredHeight;

    }else if(indexPath.item == ([self featuredItemIndex] + 1) && indexPath.item != [self numberOfItems]){
            CGFloat maxY = y + self.standardHeight;
            height = self.standardHeight + MAX((self.featuredHeight - self.standardHeight) * [self nextItemPercentageOffset], 0);
            y = maxY - height;
    }

        frame = CGRectMake(0, y, [self width], [self height]);
    attributes.frame = frame;
        [cache addObject:attributes];

        y = CGRectGetMaxY(frame);

    }

}

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    [super layoutAttributesForElementsInRect:rect];



    NSMutableArray *layoutAttributes = [[NSMutableArray alloc]initWithObjects:[UICollectionViewLayoutAttributes class], nil];

    NSLog(@"%@", cache);

    for(UICollectionViewLayoutAttributes *attributes in cache){
        if(CGRectIntersectsRect(attributes.frame, rect)){
            [layoutAttributes addObject:attributes];
        }
    }

    return layoutAttributes;

}


-(BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds{
    return true;
}

@end

NSMutableArray *layoutAttributes = [[NSMutableArray alloc]initWithObjects:[UICollectionViewLayoutAttributes class], nil];

---

这是我关于StackOverflow的第一个问题，非常感谢您的反馈和帮助。

您正在初始化时向

缓存
和
布局属性
数组添加对
UICollectionViewLayoutAttribute
类的引用。然后，调用类引用的
frame
属性（注意错误消息上的
+
，它表示类方法，其中实例方法使用
-
）

替换此行：

NSMutableArray *layoutAttributes = [[NSMutableArray alloc]initWithObjects:[UICollectionViewLayoutAttributes class], nil];

为此：

NSMutableArray *layoutAttributes = [[NSMutableArray alloc] init];

这同样适用于
缓存
变量初始化


还可以使用泛型在Objective-C中使用类型安全数组：

NSMutableArray<UICollectionViewLayoutAttributes*> *layoutAttributes = [[NSMutableArray alloc] init];

NSMutableArray*layouttributes=[[NSMutableArray alloc]init]；

更多信息