ios - UICollectionViewLayout。我的所有元素在哪里？

Question

当我在没有自定义布局对象的情况下实现 UICollectionView 时，所有 16 个可重用单元格都会出现。也就是说，我有 1 个部分，该部分中有 16 个项目。当我创建自定义布局对象时，仅显示 1 个单元格。如果我将节数更改为 5，则会出现 5 个单元格。为什么collectionView在使用布局对象时绘制部分，而在使用默认网格时绘制项目？？？我错过了什么吗？

我在这里子类化 UICollectionViewLayout:

 static NSString * const kPadLayoutType = @"gridPads";

 - (id)initWithCoder:(NSCoder *)aDecoder
 {
     self = [super initWithCoder:aDecoder];
     if(self) {
         [self setup];
     }
     return self;
 }

 - (void)setup
 {
     self.itemInsets = UIEdgeInsetsMake(22.0f, 22.0f, 13.0f, 22.0f);
     self.itemSize = CGSizeMake(125.0f, 125.0f);
     self.interItemSpacingY = 12.0f;
     self.numberOfColumns = 4;
 }

 # pragma mark _____Layout

 - (void)prepareLayout
 {
     NSMutableDictionary *newLayoutInfo = [NSMutableDictionary dictionary];
     NSMutableDictionary *cellLayoutInfo = [NSMutableDictionary dictionary];

     NSInteger sectionCount = [self.collectionView numberOfSections];
     NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:0];

     for(NSInteger section = 0; section < sectionCount; section++) {
         NSInteger itemCount = [self.collectionView numberOfItemsInSection:section];

         for(NSInteger item = 0; item < itemCount; item++) {
             indexPath = [NSIndexPath indexPathForItem:item inSection:section];

             UICollectionViewLayoutAttributes *itemAttributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
             itemAttributes.frame = [self frameForPadAtIndexPath:indexPath];

             cellLayoutInfo[indexPath] = itemAttributes;
         }
     }
     newLayoutInfo[kPadLayoutType] = cellLayoutInfo;
     self.layoutInfo = newLayoutInfo;
 }

 - (CGSize)collectionViewContentSize
 {
     return self.collectionView.frame.size;
 }

 - (NSArray *) layoutAttributesForElementsInRect:(CGRect)rect
 {
     NSMutableArray *allAttributes = [NSMutableArray arrayWithCapacity:self.layoutInfo.count];

     [self.layoutInfo enumerateKeysAndObjectsUsingBlock:^(NSString *elementIdentifier,
                                                     NSDictionary *elementsInfo,
                                                     BOOL *stop) {
         [elementsInfo enumerateKeysAndObjectsUsingBlock:^(NSIndexPath *indexPath,
                                                      UICollectionViewLayoutAttributes *attributes,
                                                      BOOL *innerStop) {
             if(CGRectIntersectsRect(rect, attributes.frame)) {
                 [allAttributes addObject:attributes];
             }
         }];
     }];
     return allAttributes;
 }

 - (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
 {
     return self.layoutInfo[kPadLayoutType][indexPath];
 }

 # pragma mark _____Private

 - (CGRect)frameForPadAtIndexPath:(NSIndexPath *)indexPath
 {
     NSInteger row = indexPath.section/ self.numberOfColumns;
     NSInteger column = indexPath.section % self.numberOfColumns;

     CGFloat spacingX = self.collectionView.bounds.size.width - self.itemInsets.left - self.itemInsets.right - (self.numberOfColumns * self.itemSize.width);

     if(self.numberOfColumns > 1) spacingX = spacingX / (self.numberOfColumns - 1);

     CGFloat originX = floorf(self.itemInsets.left + (self.itemSize.width + spacingX) * column);

     CGFloat originY = floor(self.itemInsets.top + (self.itemSize.height + self.interItemSpacingY) * row);

     return CGRectMake(originX, originY, self.itemSize.width, self.itemSize.height);
 } 

我使每个 setter 中的布局无效。

我在 UIViewController 中使用 collectionView在 viewController 中，我注册了我的 Cell 类以在 viewDidLoad 中使用并设置以下内容:

 # pragma mark - UICollectionViewDataSource

 - (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
 {
     return 16;
 }

 - (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
 {
     return 1;
 }

 - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
 {
     Pad *myPad = [collectionView dequeueReusableCellWithReuseIdentifier:kPadLayoutType forIndexPath:indexPath];
     return myPad;
 }

Answer 1

在我看来，您的 frameForPadAtIndexPath: 方法将为同一部分中的每个项目返回相同的框架，并且仅随该部分改变位置。

改变

 NSInteger row = indexPath.section/ self.numberOfColumns;
 NSInteger column = indexPath.section % self.numberOfColumns;

进入

 NSInteger row = indexPath.item/ self.numberOfColumns;
 NSInteger column = indexPath.item % self.numberOfColumns;

可能会给你更好的结果。