ARCollectionViewMasonryLayout
ARCollectionViewMasonryLayout is a UICollectionViewLayout subclass for creating flow-like layouts with dynamic widths or heights.
Usage
Create an instance of a ARCollectionViewMasonryLayout.
ARCollectionViewMasonryLayout *layout = [[ARCollectionViewMasonryLayout alloc] initWithDirection:ARCollectionViewMasonryLayoutDirectionVertical];Create a collection view. Its delegate must conform to the ARCollectionViewMasonryLayoutDelegate protocol in order to retrieve the variable dimensions of the cells.
@interface ARCollectionViewController : UICollectionViewController
@end@interface ARCollectionViewController () <ARCollectionViewMasonryLayoutDelegate>
@end
@implementation ARCollectionViewController
#pragma mark - UIViewController Lifecycle and Callbacks
- (void)viewDidLoad
{
[super viewDidLoad];
[self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"Cell"];
}
#pragma mark - UICollectionViewDataSource Methods
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
return 10;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
CGFloat colorSeed = (indexPath.row * 3 % 255)/255.0f; // random-ish color
cell.backgroundColor = [UIColor colorWithRed:colorSeed green:colorSeed blue:colorSeed alpha:1];
return cell;
}
#pragma mark - ARCollectionViewMasonryLayoutDelegate Methods
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(ARCollectionViewMasonryLayout *)collectionViewLayout variableDimensionForItemAtIndexPath:(NSIndexPath *)indexPath
{
return (CGFloat)(indexPath.row * 10 % 30) + 40; // random-ish varying size
}
@endHeaders and Footers
The masonry layout supports a fixed height header and footer that scroll along with the contents of the view. These can be added by implementing the standard UICollectionViewDelegateFlowLayout delegate methods on the UIViewController.
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
// return a header and/or footer view, must be a UICollectionReusableView
// kind is one of UICollectionElementKindSectionHeader or UICollectionElementKindSectionFooter
UICollectionReusableView *view = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:kind forIndexPath:indexPath];
view.backgroundColor = [UIColor whiteColor];
return view;
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section
{
return CGSizeMake(0, 20); // header size
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForFooterInSection:(NSInteger)section
{
return CGSizeMake(0, 20); // header size
}Sticky Headers
The layout supports having a custom sticky header ( similar to the ones in a UITableView. ) It behaves simiar to how Headers and footers work. However it needs the layout delegate to support collectionView:layout:referenceSizeForStickyHeaderInSection:.
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
[..]
} if ([kind isEqualToString:ARCollectionElementKindSectionStickyHeader]) {
UICollectionReusableView *view = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:kind forIndexPath:indexPath];
view.backgroundColor = [UIColor purpleColor];
return view;
}
[..]
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(ARCollectionViewMasonryLayout *)collectionViewLayout referenceSizeForStickyHeaderInSection:(NSInteger)section
{
return self.stickyHeaderSize;
}It also provides a callback incase you want to make transitions when the header is sticky or not:
- (void)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout stickyHeaderHasChangedStickyness:(BOOL)isAttachedToLeadingEdge
{
NSLog(@"Attached: %@", @(isAttachedToLeadingEdge));
}
Demo Project
This repository contains a demo project showing the use of the collection view layout. The view controller creates a number of ARModel instances which represent a color and dimension of a cell. These values are assigned from a collection of colors in viewDidLoad. When the collection view asks for a cell, the cell's background colour is set to the corresponding model's color. The layout queries the collection view's delegate for dimension information, and the corresponding model's dimension is returned.
License
Licensed under MIT.