A custom UICollectionViewLayout.
A sample project for objc.io Issue #3. Written by Ole Begemann, August 2013.
Please see the article for a discussion of the code.
Note that this project is only sample code and not intended to be used directly in production. In order to make the code easier to understand, I use simplified date calculations that assume a constant 7 days per week and 24 hours per day and are not based on a real calendar. To use this layout in a real calendar app, you would have to replace the computations with real NSCalendar-based date calculations.