iOS UICollectionView: The Complete Guide, Second Edition (Fahad Batla's Library) by Ash Furrow

Author:Ash Furrow
Language: eng
Format: epub, mobi
Publisher: Addison-Wesley Professional
Published: 2014-10-26T16:00:00+00:00

return self;

}

* * *

Amazing! Figure 4.5 shows we’re nearly there. The final thing I think this demo app could use is some nice animations. Support for animations is already built into UICollection-ViewLayout; we just need to implement a few methods.

Figure 4.5 Decoration views implemented

initialLayoutAttributesForAppearingItemAtIndexPath: is called whenever a new item is added or updated to the collection view. We can use it to supply initial layout attributes for the item at the beginning of the animation and the collection view will interpolate animatable properties, like frame and alpha, to their normal position. There is also a corresponding method called finalLayoutAttributesForDisappearingItemAtIndexPath: for animating removal of items from the collection view.

We can animate more than just items, though. There are corresponding appear/disappear methods for supplementary views and decoration views. The default implementation of UICollectionViewLayout returns nil, indicating a simple crossfade. We can also return nil to use a crossfade.

The remaining problem is that we reload other sections when we insert a new one. This will cause more than just the appearing sections to animate. Let’s limit which sections we animate.

Before any updates are performed to the collection view, prepareForCollectionView-Updates: is called with an array of UICollectionViewUpdateItem objects as a parameter. These are the updates that are about to happen. After they are completed, finalize-CollectionViewUpdates is called. These come in pairs. We’ll create an instance variable NSMutableSet to hold on to the sections that are being inserted. We use a set because it has constant-time lookup (see Listing 4.10).

Listing 4.10 Updated init Method to Create Mutable Set

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