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Exam AND-401 topic 1 question 102 discussion

Actual exam question from AndroidATC's AND-401

Question #: 102
Topic #: 1

[All AND-401 Questions]

Which of the following is a rule that developers must always follow when writing multi-threaded Android applications? (Choose two)

A. A worker thread must not be created from inside the UI thread.
B. Each UI thread must not create more than one worker thread.
C. The UI thread must never be blocked.
D. The Android UI must not be accessed from outside the UI thread.

Show Suggested Answer

Suggested Answer: CD 🗳️
C: If everything is happening in the UI thread, performing long operations such as network access or database queries will block the whole UI. When the thread is blocked, no events can be dispatched, including drawing events. From the user's perspective, the application appears to hang. Even worse, if the UI thread is blocked for more than a few seconds (about 5 seconds currently) the user is presented with the infamous "application not responding" (ANR) dialog.
D: The Andoid UI toolkit is not thread-safe. So, you must not manipulate your UI from a worker threadyou must do all manipulation to your user interface from the UI thread.
References:
http://developer.android.com/guide/components/processes-and-threads.html

by Mmadi at Dec. 31, 2022, 8:38 p.m.