why does the ViewHolder pattern work?

Question

I learned Android\'s ArrayAdapter today, and find there is a commom pattern which uses a ViewHolder to hold Views\' reference instead of calling findViewById everytime.

Answer 1

I believe the work beneath the list view is something like this (considering we have only one item view type):

do once:

inflate item view from layout, cache it

repeat for every item:

ask adapter to fill the data into the view
draw the view on the screen
move to next item

so you have the view which is inflated from xml layout and can be reused for drawing multiple list items. ViewHolder speeds it up a bit more by saving getViewById lookups.