We don't currently have any code published which demonstrates how the checkbox is implemented, but I can give you an overview of how we achieve this effect.
- The cell is a simple cell, which contains an instance of a custom SPCheckbox UIView subclass.
- SPCheckbox is a class which has 2 images - a ticked and an unticked version. We add a tap gesture recogniser which switches which image is currently showing.
- The SPCheckbox class also is able to update the underlying datastore through a delegate we defined.
This is not the only way that you could achieve this effect, but it's how we chose to implement it in the organize grid - I hope that it's helpful.