Android interview questions that I've faced so far or I think important

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Android Componenets

Explain briefly all the Android application components

App components are the essential building blocks of an Android app. Each component is an entry point through which the system or a user can enter your app.

There are four different types of app components:

Activities - An activity is the entry point for interacting with the user. It represents a single screen with a user interface.
Services - A service is a general-purpose entry point for keeping an app running in the background for all kinds of reasons. It is a component that runs in the background to perform long-running operations or to perform work for remote processes.
Broadcast receivers - A broadcast receiver is a component that enables the system to deliver events to the app outside of a regular user flow, allowing the app to respond to system-wide broadcast announcements.
Content providers - A content provider manages a shared set of app data that you can store in the file system, in a SQLite database, on the web, or on any other persistent storage location that your app can access.

What is an Activity?

An activity provides the window in which the app draws its UI. This window typically fills the screen, but may be smaller than the screen and float on top of other windows. Generally, one activity implements one screen in an app. For instance, one of an app’s activities may implement a Preferences screen, while another activity implements a Select Photo screen.

About Activity Lifecycle

Activity Lifecycle (in execution order) -

onCreate() - called when activity is first created.

onStart() - called when activity is becoming visible to the user.

onResume() - called when activity will start interacting with the user.

onPause() - called when activity is not visible to the user.

onStop() - called when activity is no longer visible to the user.

onRestart() - called after your activity is stopped, prior to start.

onDestroy() - called before the activity is destroyed.

Note - The onCreate() and onDestroy() methods are called only once throughout the activity lifecycle.

Uses case of activity lifecycle with execution order

When activity is opened:

onCreate()

onStart()

onResume()

When moved to another activity:

Here A == first activity and B == second activity onPause() - (A)

onCreate() - (B)

onStart() - (B)

onResume() - (B)

onStop() - (A)

when another activity is closed and moving back to first activity

onPause() - (B)

onRestart() - (A)

onStart() - (A)

onResume() - (A)

onStop() - (B)

onDestroy() - (B)

onStart vs onResume

onStart() -> called when the activity becomes visible, but might not be in the foreground (e.g. an AlertFragment is on top or any other possible use case).

onResume() -> called when the activity is in the foreground, or the user can interact with the Activity.

onPause vs onStop

onPause() -> If you can still see any part of it (Activity coming to foreground either doesn't occupy the whole screen, or it is somewhat transparent).

onStop() -> If you cannot see any part of it

A dialog, for example, may not cover the entire previous Activity, and this would be a time for onPause() to be called

General Questions

Tell me about Dependency Injection
Tell me about Jetpack Libraries
Why shoud we use an app architecture and what are the best practices?read

rohitjakhar/android-interview-questions