The Core iOS Developer’s Cookbook, Fifth Edition

Using Views with Pickers

Picker views use a basic view-reuse scheme, caching the views supplied to it for possible reuse. When the final parameter for the pickerView:viewForRow:forComponent:reusingView: method is not nil, you can reuse the passed view by updating its settings or contents. Check for the view and allocate a new one only if one has not been supplied.

The height need not match the actual view. Implement pickerView:rowHeightForComponent: to set the row height used by each component. Recipe 9-8 uses a row height of 120 points, providing plenty of room for each image and laying the groundwork for the illusion that the picker could be continuous rather than having a starting point and an ending point.

Notice the high number of components: ...