2022 latest Android interview written examination, an Android programmer's interview experience

Preface

The interview situation this year is not optimistic , The competition is getting fiercer , The difficulty of entering a large factory has increased . however , Dreams are necessary , What if it does ？ There is a lucky goose .

A friend of mine , A few days ago , His circle of friends, which has not been updated for a hundred years, has new developments , He was exposed to the sun offer, The accompanying copy is the title of this article ： The algorithm is too TM It's important ！ Finish these questions , I finally got the big factory I dreamed of offer！

There are many friends who come to congratulate Xi , It's the sour speech .

1. Routing in componentization 、 The realization of buried point

Reference answer ：

Because in componentization , Each business module is independent ,  There is no interdependence ,  So one business module cannot access the code of other business modules ,  If you want to go from  A  Business module  A  The page jumps to  B  Business module  B  page ,  It can't be realized by the module itself , This requires a cross component communication solution ——  route （Router）

There are two main scenarios for routing :

• The first is the page jump between components  (Activity  To  Activity, Fragment  To  Fragment, Activity  To  Fragment, Fragment  To  Activity)  As well as data transfer during jump  ( Basic data types and serializable custom class types )

• The second is the call of custom classes and methods between components ( Components provide services to the outside )

The principle is that it will be distributed among different components module Some classes in generate mapping tables according to certain rules （ Data structures are usually Map,Key For a string ,Value For a class or object ）, Then, when needed, the class or object is extracted from the mapping table according to the string , It's essentially a class lookup

Buried point is to collect some information in the specific process of application , Used to track application usage

• Code buried point
  ： Call... When an event occurs SDK The corresponding interface inside sends buried point data , Baidu statistics 、 umeng 、TalkingData、Sensors Analytics The third-party data statistics service providers mostly adopt this scheme

• Full buried point
  ： Full buried point refers to Web page /App All that comes from within 、 The act of satisfying a condition , All reports to the background server

• Visual burying point
  ： Through visualization tools （ for example Mixpanel） Configure the collection node , stay Android The end automatically analyzes the configuration and reports the buried point data , So as to realize the so-called automatic embedding point

• No burying point
  ： It doesn't really need to be buried , It is Android The terminal automatically collects all events and reports the buried point data , Filter out useful data in the back-end data calculation

2.Hook And pile insertion technology

Reference answer ：

Hook It's a way to change API Techniques for executing results , Be able to make the system API Function to perform redirection （ The trigger event and background logic processing of the application are executed step by step according to the event process . and Hook It means , It is to intercept and monitor the transmission of events before they are transmitted to the destination , Like a hook on an event , And be able to hook up events , Handle  

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  Some own specific events , For example, reverse cracking App）

Android  Medium  Hook  Mechanism , There are roughly two ways ：

• want  root  jurisdiction , direct  Hook  System , Can kill all  App.

• nothing  root  jurisdiction , But only  Hook  Oneself app, For other systems  App  incapable of action .

Pile insertion is a static way to modify third-party code , That is, from the compilation stage , To source code （ Intermediate code ） Compile , Then repackage , It's static tampering ;  and Hook There is no need to modify the third-party source code or intermediate code in the compilation stage , Is to modify the call by reflection at run time , Is a dynamic tampering

3.Android Signature mechanism of ？

Reference answer ：

Android The signature mechanism of includes message digest 、 Digital signatures and digital certificates

• A summary of the news
  ： On message data , Perform a one-way  Hash  function , Generate a fixed length of Hash value

• digital signature
  ： A method of storing message signatures in electronic form , A complete digital signature scheme should consist of two parts ： Signature algorithm and verification algorithm

• digital certificate
  ： A certificate authorized （Certificate Authentication） Central digital signature file containing public key owner information and public key

4.Android5.0~10.0 A big change between

Reference answer ：

4.1.Android5.0 New characteristics

• MaterialDesign Design style

• Support 64 position ART virtual machine （5.0 To launch the ART virtual machine , stay 5.0 Before is Dalvik. The difference between them is ：Dalvik, Each run , Bytecode needs to be converted into machine code by an instant compiler (JIT). ART, The first time I installed the app , Bytecode will be precompiled into machine code (AOT)）

• The notification details can be designed by users themselves

4.2.Android6.0 New characteristics

• Dynamic authority management

• Support fast charging switching

• Supports folder drag and drop applications

• Camera new professional mode

4.3.Android7.0 New characteristics

• Multi window support

• V2 Signature

• Enhanced Java8 Language patterns

• Night mode

4.4.Android8.0（O） New characteristics

• Optimization notification ： Notification channels  (Notification Channel)  Notice sign   Sleep   Notification timeout   Notification settings   Notice to clear

• Picture in picture mode ： In the list Activity Set up android:supportsPictureInPicture

• Background restrictions

• Auto fill frame

• system optimization

• And so on

4.5.Android9.0（P） New characteristics

• indoor WIFI location

• “ bang ” Screen support

• Security enhancements

• And so on

4.6.Android10.0（Q） New characteristics

• Night mode ： All apps, including mobile phones, can set the dark mode for them .

• Desktop mode ： Offer something similar to PC Experience , But it was far substitute PC.

• Screen Recording ： By long press “ Power Supply ” Menu " Screenshot " To open .

5. Under the said Measurepec This class

Reference answer ：

effect

： Through the wide measurement widthMeasureSpec And high measurements heightMeasureSpec decision View Size

form

： One 32 position int value , high 2 On behalf of SpecMode( Measurement mode ), low 30 On behalf of SpecSize(  Specification size in a measurement mode ).

Three models ：

• UNSPECIFIED： The parent container is not right View There are any restrictions , How big, how big . It is often used inside the system .

• EXACTLY( Accurate model )： The parent view specifies an exact size for the child view SpecSize. Corresponding LyaoutParams Medium match_parent Or specific values .

• AT_MOST( Maximum mode )： The parent container specifies a maximum size for the child view SpecSize,View The size of cannot be greater than this value . Corresponding LayoutParams Medium wrap_content.

determinant ： Value by child View The layout parameters of LayoutParams And the parent container MeasureSpec It's up to you to decide . The specific rules are shown in the figure below ：

6. Please give an example of Android Layout types are commonly used in , And describes its usage and typesetting efficiency

Reference answer ：

Android The commonly used layout is divided into traditional layout and new layout

• Traditional layout （ To write XML Code 、 Code generation ）：

• Frame layout （FrameLayout）：

• Linear layout （LinearLayout）：

• Absolute layout （AbsoluteLayout）：

• Relative layout （RelativeLayout）：

• Table layout （TableLayout）：

• New layout （ Visual drag and drop control 、 To write XML Code 、 Code generation ）：

• Constrained layout （ConstrainLayout）

• 

• For nested layers View for , Its typesetting efficiency ：LinearLayout = FrameLayout >> RelativeLayout

7. difference Animation and Animator Usage of , Summarize its principle

Reference answer ：

• Types of animation
  ： The former has only transparency , rotate , translation , Telescopic 4 Species attribute , And for the latter , As long as it is the property of the control , And there are setter The methods of the attribute can perform a dynamic change effect on the attribute .

• Operational objects
  ： The former can only UI Component execution animation , But attribute animation can animate almost any object （ Whether it's on the screen or not ）.

• Animation playback order
  ： stay Animator in ,AnimatorSet It is through playTogether()、playSequentially()、animSet.play().with()、before()、after() These methods are used to control multiple animations to work together , So as to achieve accurate control of the animation playback sequence

• 

8. What image loading libraries have been used ？Glide Where is the source code design subtle ？

Reference answer ：

• Image loading Library ：Fresco、Glide、Picasso etc.

• Glide The subtlety of the design is ：

• Glide Life cycle binding
  ： You can control the loading status of the picture to synchronize with the life cycle of the current page , Make the whole loading process start with the state of the page / recovery , stop it , The destruction

• Glide Cache design
  ： adopt （ Three level cache ,Lru Algorithm ,Bitmap Reuse ） Yes Resource Cache design

• Glide The complete loading process
  ： use Engine The engine class exposes a series of methods for Request operation

9. How to bypass the 9.0 Limit ？

Reference answer ：

10. How to do this for application update ？ （ Grayscale , Force update 、 Sub regional update ）

Reference answer ：

10.1. Internal update ：

• Get the online version number through the interface ,versionCode

• Compare Online versionCode  And local versionCode, The update window pops up

• download APK file （ File download ）

• install APK

10.2. Gray update ：

• Find a single channel to launch a special version .

• Upgrade the platform , It is allowed to push upgrade notifications and even force version upgrades for some users .

• Open a separate download portal .

• Both versions of the code hit app In the bag , And then in app End implant test framework , Used to control which version is displayed . The test framework is responsible for communicating with the server side api signal communication , Controlled by the server app On A/B Distribution of versions , A specified group of users can see A edition , Other users see B edition . The server will have corresponding reports to display A/B Quantity and effect comparison of versions . Finally, it can be controlled by the background of the server , All users switch online to A perhaps B edition ~

• Either way, you need to do a good job of version management , Assign a special version number to distinguish .  Of course , Since it's gray scale , Data monitoring （ General data 、 New feature data 、 Main business data ） We still have to do it in place , The data pile to be driven should be driven .  also , Grayscale version should have the ability to recover , Generally, it is forced to upgrade to the next official version .

10.3. Force update ：

The general process is to enter the application and pop up a window to notify the user that there is a version update , The pop-up window cannot be cancelled without the Cancel button . In this way, users can only choose to update or close the application , Of course, you can also add a cancel button , However, if the user chooses to cancel, he will exit the application directly .

10.4. Incremental updating ：

Binary difference tool bsdiff Is the corresponding patch synthesis tool , According to two different versions of binary files , Generate patch file .patch file . adopt bspatch Make the old apk File and indefinite file compose new apk.  Pay attention to pass apk Of documents md5 Value to distinguish versions .

11. Will use Kotlin、Fultter Do you ？  Talk about your understanding

Reference answer ：

• Kotlin Is a cross platform with type inference , General purpose programming language for static types . Kotlin Aim at and Java Full interoperability , Of its standard library JVM Versions depend on Java Class library , But type inference allows its syntax to be more concise .

• Flutter By Google Create an open source mobile application development framework . It is used for development Android and iOS Applications for , As well as Google Fuchsia The main way to create an application

• About kotlin Importance , I believe you can experience in daily development , Apply to actual development , Grammar sugar needs to be avoided （ For example, single column mode 、 A null value judgment 、 Higher order functions, etc ）

• as for Flutter, at present Google The official documents are not perfect , There are few projects written in this language on the market , If you need to be specific , Please refer to the official documentation

The end of the

For many primary and intermediate Android For Engineers , Want to improve skills , Often is oneself gropes for growth , Unsystematic learning is inefficient, long and helpless .  I hope that these architecture technologies can be applied to Android Development of friends have reference and less detours , The point of this article is whether you have gained and grown up , The rest is unimportant , I hope readers will keep this in mind .

Finally, we want to get a high salary to improve technology and get a qualitative leap in salary . The quickest way , That is, someone can take you with them to analyze , This is the most efficient way to learn , So in order to advance to the middle and senior level smoothly 、 Architects , I specially prepared a set of master learning source code and framework videos for you Android Architect tutorial , Make sure you learn to make sure your salary goes up to a higher level .

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• When you have a learning path , What to learn , I also know how to go in the future , If you see too much theory, you have to practice it .