The summary.
A DEFECT SHIPPED MAY PERSIST ON DEVICES FOR MONTHS
Users do not update immediately and some never do, which is why you need care before release and the ability to disable features remotely.
THE SYSTEM CAN TERMINATE YOUR APPLICATION WITHOUT WARNING
Save state as it changes, not on exit, and never assume you get a chance to save. What users notice most is losing what they entered.
Release resources on backgrounding — an application consuming battery in the background gets uninstalled.
ANDROID DOMINATES THIS MARKET, ACROSS A WIDE RANGE OF DEVICE CAPABILITY
Which makes Android first the right default here. And iOS development requires Apple hardware without exception, which is a real cost barrier.
TEST ON A MODEST PHYSICAL DEVICE FIRST
Emulators and development hardware conceal performance, battery use, touch behaviour and real network conditions.
KEEP EVERYTHING SLOW OFF THE MAIN THREAD
Blocking it freezes the interface and the system may report your application as unresponsive.
RESPECT THE USER'S CHOSEN FONT SIZE
Ignoring it makes the application unusable for people who need larger text.
