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Author: Yin Star

Original Article: http://www.jianshu.com/p/a22450882af2

Introduction

As the year-end bonuses are distributed, many Android developers might be gearing up for interviews. Combining my past experiences, today I will summarize some Android interview questions that I hope will be helpful.

01

What is the Activity lifecycle?

This is a classic question that will never go out of style and is likely to be the first question asked. There’s really not much to say about this question; rote memorization won’t help much, understanding is key. I once encountered a variant of this question asking about the difference between onStart() and onResume(). If the interviewer throws this question at you, it might catch you off guard. Today, I heard that a classmate faced an even trickier question: Under what circumstances does an Activity go through onCreate() but not onStart()? This is simply a brain teaser.

02

What is the Service lifecycle?

Here, it’s important to note that there are two ways to start a service: startService() and bindService()

03

Understanding the relationship between Activity, View, and Window

This question is really difficult to answer. So let’s start with a metaphor to describe their relationship. An Activity is like a craftsman (control unit), a Window is like a window (holding the model), a View is like a decorative window (displaying the view), LayoutInflater is like scissors, and XML configuration is like the design of the decorative window. 1: When an Activity is constructed, it initializes a Window, specifically a PhoneWindow. 2: This PhoneWindow has a “ViewRoot,” which is a View or ViewGroup, the initial root view. 3: The “ViewRoot” adds Views one by one via the addView method, such as TextView, Button, etc. 4: The event listeners for these Views are handled by WindowManagerService, which receives messages and callbacks to Activity functions, like onClickListener, onKeyDown, etc.

04

The four types of LaunchMode and their usage scenarios

standard mode This is the default mode; each time the Activity is activated, a new instance of the Activity is created and placed in the task stack. Usage scenario: Most Activities. singleTop mode If an instance of that Activity already exists at the top of the task stack, it reuses that instance (calls onNewIntent()), otherwise it creates a new instance and places it at the top of the stack. Even if an instance of that Activity exists in the stack, as long as it is not at the top, a new instance will be created. Usage scenarios include news or reading apps. singleTask mode If an instance of that Activity already exists in the stack, it reuses that instance (calls onNewIntent()). When reused, that instance will be brought to the top of the stack, and any instances above it will be removed from the stack. If that instance does not exist in the stack, a new instance will be created and placed in the stack. Usage scenarios include the main interface of a browser. Regardless of how many applications start the browser, only the main interface will be started once, and other instances will call onNewIntent, clearing other pages above the main interface. singleInstance mode Creates an instance of that Activity in a new stack and allows multiple applications to share that Activity instance in that stack. Once an instance of that Activity in this mode exists in a stack, any application activating that Activity will reuse the instance in that stack (calls onNewIntent()). Its effect is similar to multiple applications sharing one application; regardless of who activates that Activity, they will enter the same application. Usage scenarios include alarm reminders, separating alarm reminders from alarm settings. singleInstance should not be used for intermediate pages; if used for intermediate pages, navigation will have issues, for example: A -> B (singleInstance) -> C, after fully exiting, starting here will first open B.

05

View rendering process

Measure processLayout processDraw process No more worries about custom Views – Detailed explanation of Android custom views

Android View rendering source code analysis (part 1)

Android View rendering source code analysis (part 2)

06

Touch event passing mechanism

public boolean dispatchTouchEvent(MotionEvent ev);  
// Used to dispatch event
public boolean onInterceptTouchEvent(MotionEvent ev);  
// Used to intercept event
public boolean onTouchEvent(MotionEvent ev);  
// Used to handle event

Both Activity and View controls (TextView) have methods to dispatch and handle events, while View containers (LinearLayout) have methods to dispatch, intercept, and handle events. Here’s a metaphor: Leaders delegate tasks downward; if the people below do not do well, they will not delegate further tasks to them, but will do it themselves. If they cannot do it either, they can only report to their superiors that they cannot complete the task, and their superiors will repeat this process. Additionally, leaders have the authority to intercept tasks, directly doing them themselves while hiding the task from subordinates. If they cannot complete it, they can only report to their superiors.

07

Several types of animations in Android

I was once asked how many types of animations there are in Android, and this question is quite difficult to answer. Before Android 3.0, there were 2 types, and after 3.0, there are 3 types. FrameAnimation (frame animation): Combines multiple images for playback, similar to the working principle of early movies; many apps use this method for loading. TweenAnimation (tween animation): A series of animations applied to a View, including fade in and out (Alpha), scaling (Scale), translation (Translate), and rotation (Rotate). PropertyAnimation (property animation): Property animation is no longer just a visual effect but a mechanism for continuously operating on values and assigning them to specified properties of specified objects, which can be any property of any object.

Android animations, this is enough after reading these (part 1)

Android animations, this is enough after reading these (part 2)

http://blog.csdn.net/yanbober/article/details/46481171

08

Several ways of inter-process communication in Android

1: Accessing other applications’ Activities For example, calling the system dialer application

Intent callIntent = new Intent(Intent.ACTION_CALL, Uri.parse("tel:12345678"));
startActivity(callIntent);

2: Content Provider For example, accessing the system gallery

3: Broadcast For example, displaying system time

4: AIDL service

09

Understanding AIDL

http://bbs.51cto.com/thread-1086040-1.html

10

Principles of Handler

IntentService – Combining Handler and Service

Optimizing runtime speed and performance in Android development using asynchronous methods

In-depth understanding of ThreadLocal (part 1)

http://blog.csdn.net/lmj623565791/article/details/38377229

11

Principles of the Binder mechanism

Why does Android use Binder as the IPC mechanism?

http://blog.csdn.net/boyupeng/article/details/47011383

12

Principles of hotfixing

1: JavaSisst 2: AspectJ 3: Xposef Alibaba’s Android hotfix technology selection – Analysis of three major factions

Analysis of Android hotfix solutions

Android hot update: Meituan’s hot update solution for Android Robust

Using AndFix for hotfix in Android pluginization

13

Designing an image asynchronous loading and caching solution

http://www.cnblogs.com/zyw-205520/p/4997863.html http://blog.csdn.net/boyupeng/article/details/47127605

14

Memory leaks and management in Android

Research on Android memory leaks

Summary of Android memory leaks (part 2)

Android memory performance optimization (internal material summary)

5 common memory leak issues in Android development and their solutions

Actual cases of locating and solving Android memory leak issues

[Valuable Resource] Practical analysis and insights on Android memory leaks – Common interview points

Discussing Android memory leaks again – Eight common problems leading to APP memory leaks

The most comprehensive and systematic Android interface performance tuning materials

http://gold.xitu.io/entry/56d64b9e816dfa005943a55c

15

Communication between Activity and Fragment

[Valuable Resource] Understanding Context thoroughly, if you don’t get it, how can you do Android development?

http://gold.xitu.io/entry/56a87b2b2e958a0051906227

16

Pits of Fragment

http://www.jianshu.com/p/d9143a92ad94 http://www.jianshu.com/p/fd71d65f0ec6 http://www.jianshu.com/p/38f7994faa6b

17

Android UI adaptation

Summary of Android UI layout issues

Embracing SVG: Struggling with image adaptation in Android? Universal image adaptation

http://blog.csdn.net/lmj623565791/article/details/45460089

18

Layout optimization

Android performance optimization series – Improving Layout Performance (part 1)

Android performance optimization series – Improving Layout Performance (part 2)

Android performance optimization series – Improving Layout Performance (part 3)

Performance optimization in layout

Practical tips for Android layout optimization

Suggestions for efficient Android layouts

What is ConstraintLayout introduced at Google I/O 2016? A new world of Android Layout

Summary of Android UI layout issues

Performance analysis of RelativeLayout and LinearLayout in Android

Overdraw optimization in Android layout

http://www.jianshu.com/p/145fc61011cd

19

HTTP and HTTPS

Simple introduction to common communication protocols HTTP, TCP, UDP

Discussing what the HTTP protocol does based on daily development

The most detailed introduction to HTTPS

Explaining how HTTPS ensures security?

http://www.jianshu.com/p/93fdebe5fef1

20

Network request optimization

Practical experience in network performance optimization of the Ctrip App

Research on Android push technology

http://www.jianshu.com/p/3141d4e46240

21

Database optimization

Performance optimization issues of SQLite on Android

Analysis of SQLite’s locking mechanism and WAL technology

http://www.jianshu.com/p/3b4452fc1bbd

22

Image optimization

Comparison of the three major image caching principles and characteristics in Android

The most comprehensive and detailed explanation of Facebook’s powerful Android image loading framework Fresco

Getting to know Facebook’s powerful Android image loading framework: Fresco

Embracing SVG: Struggling with image adaptation in Android? Universal image adaptation

http://www.jianshu.com/p/5bb8c01e2bc7

23

Hybrid JAVA and JS interaction

Communicating well with H5! Several common hybrid communication methods

A glimpse into hybrid mobile app development with Ionic

Douban hybrid development practice

http://droidyue.com/blog/2014/09/20/interaction-between-java-and-javascript-in-android/

24

Singleton design pattern

Detailed explanation of the singleton design pattern

25

Java GC principles

Research on Android memory leaks

Understanding the architecture of the Android virtual machine

JVM Insights: Detailed explanation of the Java virtual machine

http://www.jianshu.com/p/d75a32ac5bed?

26

ANR

Android performance optimization series – Avoiding ANR

http://www.jianshu.com/p/124f3b75e164

27

Volley

Dribbble client based on MVP architecture and MD style

http://www.jianshu.com/p/9e17727f31a1

28

Java annotation reflection principles

http://www.jianshu.com/p/3968ffabdf9d

29

Algorithms

10 essential practical algorithms every programmer should know and their explanations

Algorithm fun talks – Comic: Judging the power of 2 – Making algorithm learning less tedious

[Fun Talks on Algorithms Series]: The maximum adjacent difference after sorting an unordered array

http://www.jianshu.com/p/ae97c3ceea8d

30

Design patterns

Detailed explanation of the Adapter design pattern

Summary of the Observer pattern

Detailed explanation of the Singleton design pattern

The “Memento pattern” is that simple

The design architecture of Android Apps: MVC, MVP, MVVM and architectural experiences

http://gold.xitu.io/entry/56ebb4ad5bbb50004c440972

31

RxJava

Constructing a clear framework for Android using RxJava

Airbnb: How our Android client uses RxJava

A great Android APP framework

http://gank.io/post/560e15be2dca930e00da1083?from=timeline&isappinstalled=0#toc_1

32

MVP, MVC, MVVM

Analysis of the official MVP architecture example project from Android

Interpretation of the official MVP architecture example project from Android

The design architecture of Android Apps: MVC, MVP, MVVM and architectural experiences

A brief discussion on Android programming thoughts and architecture

APP refactoring: From MVC architecture to MVP architecture in Android practice

Practical experience in Android open-source: Developing a text reading APP using MVP + Retrofit

http://blog.csdn.net/pkxiuluo01/article/details/49383783

33

React Native cross-platform technology

Popularizing React Native – The hottest front-end technology currently

Practical integration of React Native for Android

https://mp.weixin.qq.com/s/i0DWHR2eQmNijXTQv3YGmQ

35

Android 5.0

Dribbble client based on MVP architecture and MD style

An APP developed based on Retrofit2.1 + Material Design + ijkplayer (news, gif, video playback)

http://www.androidchina.net/1381.html

36

Android 6.0 runtime permissions

Android 6.0 permission adaptation, simpler than you think (practical part)

Android 6.0 (API level 23) includes various system changes and API behavior changes

Understanding the touch event distribution mechanism in Android 6.0

https://mp.weixin.qq.com/s/R2sAthMB2yW3ytTesnT-Jw

37

New features of Android 7.0

Summary of new features in Android 7.0, look at what unexpected things Google has?

Tutorials and insights on adapting to Android 7.0

Top 10 new features of Android N that everyone is looking forward to

http://blog.csdn.net/wds1181977/article/details/52292445

38

Android pluginization and compositional development

Using AndFix for hotfix in Android pluginization

The principle of Android sub-packaging

One implementation of Android pluginization

The cornerstone of pluginization is APK dynamic loading

Tuniu Original | The realization of plugins in Tuniu’s Android App

http://www.cnblogs.com/android-blogs/p/5703355.html

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