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CHAPTER 4
Pickers
4-14 List Pickers
Hierarchical List Pickers 4
If a list of picker items is extremely long, index tabs won’t be enough to
prevent interminable scrolling. What happens is a user taps a tab and
immediately sees the beginning of the corresponding section of picker items,
but the user still must scroll several times to find an item that’s not near the
beginning of that section. For example, imagine one picker that lists several
hundred cities from around the world.
The solution to this situation is to create a two-level hierarchy of list pickers.
The first-level picker contains a set of picker items and a diamond label.
Tapping the diamond label pops up a second-level picker that lists different
sets of picker items for the first-level picker. Picking an item in the second-level
picker determines which set of items appear in the first-level picker. For
example, compared to a single picker that lists hundreds of cities, a two-level
picker hierarchy simplifies picking a city anywhere in the world. The first-
level picker lists cities for just one country and contains the name of the
country as a diamond label. A user can pick one of the listed cities or tap the
diamond label to pop up a second-level picker that lists other countries. If
the user picks a country, then the first-level picker changes to list that country’s
cities. Figure 4-11 shows how the city and country hierarchical pickers work.