Enhanced transitioning between UICollectionView layouts in iOS.
##Overview
TLLayoutTransitioning provides a TLLayoutTransition transition layout subclass and a UICollectionView+TLTransitioning category that combine to solve a few problems with collection view layout transitioning:
-
UICollectionViewLayoutTransitiondoes not handle content offset well, often leaving cells where you don't want them.TLTransitionLayoutprovides elegant control of content offset with Minimal, Visible, Center, Top, Left, Bottom or Right placement options relative to one or more index paths. -
UICollectionViewLayoutTransitiondoes not support supplementary views.TLTransitionLayoutprovides support for any supplementary view kinds specified in the initializer. -
-[UICollectionView setCollectionViewLayout:animated:completion]has serious known bugs in iOS7 and does not provide any animation options. TLLayoutTransitioning provides a robust alternative to this API with support for animation duration, 30+ easing curves and content offset control. This is done by usingCADisplayLinkto drive an interactiveTLTransitionLayoutas a non-interactive animation. Note that this approach may not perform as well as Core Animation with more complex cells.
Check out the demos in the Examples workspace!
###TLTransitionLayout Class
TLTransitionLayout is a subclass of UICollectionViewTransitionLayout that interpolates linearly between layouts and optionally between the current content offset and a specified final offset.
The final offset is specified
by setting the toContentOffset property. The UICollectionView+TLTransitioning category
provides an API for calculating Minimal, Visible, Center, Top, Left, Bottom or Right offset placements relative to one or more index paths.
The basic usage is as follows:
- (void)someViewControllerEventHandler
{
UICollectionViewLayout *nextLayout = ...;
self.transitionLayout = (TLTransitionLayout *)[self.collectionView startInteractiveTransitionToCollectionViewLayout:nextLayout
completion:^(BOOL completed, BOOL finish) {
if (finish) {
self.collectionView.contentOffset = self.transitionLayout.toContentOffset;
self.transitionLayout = nil;
}
}];
NSArray *indexPaths = ...;// some selection of index paths to place
self.transitionLayout.toContentOffset = [self.collectionView toContentOffsetForLayout:self.transitionLayout indexPaths:indexPaths placement:TLTransitionLayoutIndexPathPlacementCenter];
}
- (UICollectionViewTransitionLayout *)collectionView:(UICollectionView *)collectionView transitionLayoutForOldLayout:(UICollectionViewLayout *)fromLayout newLayout:(UICollectionViewLayout *)toLayout
{
NSArray *supplementaryKinds = ...; // optional supplementary view kinds
return [[TLTransitionLayout alloc] initWithCurrentLayout:fromLayout nextLayout:toLayout supplementaryKinds:supplementaryKinds];
}
Note that the collection view will reset contentOffset after the transition is finalized, but as illustrated above, this can be negated by setting it back to toContentOffset in the completion block.
####Canceling a Transition
If you want to stop the current transition to start a new one from the current position, you need a way to stop the current transition in-place. Apple provides finishInteractiveTransition and cancelInteractiveTransition to end a transition, but neither of these stops the transition in-place. So, TLLayoutTransitioning provides such a method:
[self.collectionView cancelInteractiveTransitionInPlaceWithCompletion:^(){
// initiate new transition in the completion block
}];You can find out if a transition is currently in progress by checking the isInteractiveTransitionInProgress on UICollectionView.
###UICollectionView+TLTransitioning Category
The UICollectionView+TLTransitioning category provides some of useful methods for calculating for interactive transitions. In particular, the toContentOffsetForLayout:indexPaths:placement API calculates final content offset values to achieve Minimal, Visible, Center, Top, Left, Bottom or Right placements for one or more index paths. The expanded version of this API provides for even further fine-tuning and supports transitioning to a different collection view size and content inset:
- (CGPoint)toContentOffsetForLayout:(UICollectionViewTransitionLayout *)layout
indexPaths:(NSArray *)indexPaths
placement:(TLTransitionLayoutIndexPathPlacement)placement
placementAnchor:(CGPoint)placementAnchor
placementInset:(UIEdgeInsets)placementInset
toSize:(CGSize)toSize
toContentInset:(UIEdgeInsets)toContentInset
UICollectionView+TLTransitioning also provides an alternative to -[UICollectionView setCollectionViewLayout:animated:completion] for non-interactive animation between layouts with support for animation duration, 30 built-in easing curves (courtesy of Warren Moore's AHEasing library), user defined easing curves (by defining custom AHEasingFunctions) and content offset control. The basic transition call is as follows:
TLTransitionLayout *layout = (TLTransitionLayout *)[collectionView transitionToCollectionViewLayout:toLayout duration:2 easing:QuarticEaseInOut completion:nil];
CGPoint toOffset = [collectionView toContentOffsetForLayout:layout indexPaths:@[indexPath] placement:TLTransitionLayoutIndexPathPlacementCenter];
layout.toContentOffset = toOffset;where the view controller is configured to provide an instance of TLTransitionLayout as described above. Check out the Resize sample project in the Examples workspace to see this in action.
##Installation
###CocoaPods
Add the following to your Podfile
pod 'TLLayoutTransitioning'
###Carthage
Add the following to your Cartfile
github "wtmoose/TLLayoutTransitioning"
Note that TLLayoutTransitioning has a dependency on AHEasing, which
does not support Carthage. As a workaround, TLLayoutTransitioning's Cartfile uses the wtmoose/AHEasing fork which adds Carthage support.
To request Carthage support for the canonical AHEasing library, consider leaving a comment in favor of reopening the Add dynamic frameworks support pull request.
###Manual
If you're not using a dependency manager, check out the noframeworks branch and copy the following files into your project:
TLTransitionLayout.h
TLTransitionLayout.m
UICollectionView+TLTransitionAnimator.h
UICollectionView+TLTransitionAnimator.m
And copy the following files from AHEasing:
easing.h
easing.c
##Examples
Open the Examples workspace (not the project) to run the sample app. The following examples are included:
###Resize
The Resize example combines TLTransitionLayout and -[UICollectionView+TLTransitioning transitionToCollectionViewLayout:duration:easing:completion:] as a better alternative to -[UICollectionView setCollectionViewLayout:animated:completion]. Experiment with different durations, easing curves and content offset options on the settings panel. Toggle "show section headers" to see transitioning supplementary views.
###Pinch
The Pinch example demonstrates a simple pinch-driven interactive transition using TLTransitionLayout. The destination contentOffset is selected such that the initial visible cells remain centered. Or if a cell is tapped, the contentOffset the cell is centered.
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