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POUICollectionViewLayout. Where are all my items?
 

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  1. POUICollectionViewLayout. Where are all my items?
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    <p>When I implement UICollectionView without a custom layout object, all 16 of my reusable cells appear. That is, I have 1 section with 16 items in that section. When I create a custom layout object, only 1 cell appears. If I change # of sections to 5, then 5 cells appear. Why does the collectionView draw sections when using a layout object, and items when using the default grid???? Am I missing something?</p> <p>I subclass UICollectionViewLayout here:</p> <pre><code> 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 &lt; sectionCount; section++) { NSInteger itemCount = [self.collectionView numberOfItemsInSection:section]; for(NSInteger item = 0; item &lt; 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 &gt; 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); } </code></pre> <p>I invalidate the layout in each setter.</p> <p>I am using a collectionView within my UIViewController In the viewController I register my Cell class for use in viewDidLoad and setup the following:</p> <pre><code> # 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; } </code></pre>
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A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

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