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Debugging a DiffableDataSource CellProvider

11 July 2021

I was recently working on a project that uses modern collection views on iOS — that is, using diffable data sources, snapshots, and cell providers. I hooked up all the components and my collection view was working, or so I thought. I started to notice some very odd, unpredictable behavior when the collection view was updated. Some of the time, the cells were updated correctly. Other times, I would see duplicates and missing data. Here’s what went wrong.