Introduction

It's interview season again , I had to take part in the battle myself , In fact, it started from the end of last year ,Android There are not many good opportunities , But it's ok ,3 year + Of android There are still some interview opportunities for the development experience , But the threshold is not as low as it was a few years ago , The general experience is that small start-ups pay more attention to whether your project experience fits with your own , Just come and be alone .

In addition to focusing on the project experience, big factories , Also pay more attention to the breadth of your knowledge , It's breadth 、 In depth and solutions , You should accumulate enough work at ordinary times and brush questions temporarily. It's estimated that you can't pass the test if you only talk about superficial questions . The following is a summary of some knowledge points that will be asked in the interview of large factories , I sorted out the best videos on the Internet , There are all kinds of styles .

The interviewer asked a question , Let's see A、B and C How are the three students doing

A

interviewer ： say something Application The role of .

A：Application It is a system component that will be created after the application process is created , So you can use it to do some initialization ;Application The life cycle is as long as the application process , So it can be used to provide... For class libraries Context; Because in all Context You can get Application So it can be used to save and pass global variables .

interviewer ： You usually put global variables in Application ? The app is recycled in the background , What if the value is lost when reopening ？

A： yes , Very convenient , Just make a fault-tolerant judgment

interviewer ： well , Go back and wait for the announcement

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B

interviewer ： Say yes Application The understanding of the

B： effect ： Do initialization 、 Provide context . in addition Application It's a Context , It inherits directly ContextWrapper ; This ContextWrapper Member variables of mBase Can be used to store the system implementation ContextImpl, So we're calling Application Of Context When the method is used , They are finally called to... Through static proxy ContextImpl Methods . We call ContextWrapper Of getBaseContext The way to get it ContextImpl Example

interviewer ： You usually put global variables in Application ? The app is recycled in the background , What if the value is lost when reopening ？

B： Can't , Save global variables with static variables , Or a single example can gather them in a more appropriate position .
Avoid application recycling and data loss , When you can pass parameters to a page , adopt Intent Pass parameters , This is recycled and reopened from Intent There is still value in taking parameters . If the amount of data is large, you can also consider data persistence ; Another way is through onSaveInstanceState and onRestoreInstanceState Save the corresponding data when it is recycled and restore the data when it is reopened .

interviewer ： Let's talk about Application Life cycle of

B： comparison Activity ,Application The life cycle of is simply not too simple . First, the constructor will be called when it is created , Then the system is ready ContextImpl adopt attachBaseContext( Context ) Method injection into Application, Then call our most familiar onCreate Method .API There's one more onTerminate Method will call back when the process is killed , But only if the simulator works , You don't need to pay attention .

interviewer ： Then you can go on Application The initialization process of ？

B： Basically the ones mentioned above , I didn't understand it in detail

interviewer ： well , Go back and wait for the announcement

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C

interviewer ： The way Application Initialization process of

C：Application The initialization of is after the application process is created ：

ActivityThread call AMS Of Binder object （ IActivityManager ） Of attachApplication Method
AMS After receiving the request, call ActivityThread Of bindApplication Method
ActivityThread We received a request here to assemble another AppBindData object , Encapsulate all parameters , Re pass handler Send to the main thread to execute

The main thread loop To this message , call handleBindApplication To actually handle initialization Application

handleBindApplication Talk to us “Context” That ,Activity The initialization of is almost the same . Take a look back. ：

ClassLoader load Application class , Instantiation
initialization Applicaction With ContextImpl
adopt Application.attach( Context ) Method , call attachBaseContext( Context ) take ContextImpl Injection into Application
Last call Application.OnCreate()

such Application Initialization is complete

interviewer ： Why don't you call directly when the process is created handleBindApplication To create Application Well , Go again AMS There was a circle over there

C： call AMS Of attachApplication Not just to create Application , In addition, before the process is created, the four components of the application may be called but cannot be started ; Now the process is created , Create good Application Also deal with these components to be started . So you have to go through AMS Unified scheduling , If Application Creation and onCreate If the callback takes time , It will also affect the startup time of these components to be started

interviewer ： Sure , Let's talk about something else .

Last

For the convenience of friends who need to learn , I organized the materials into a video tutorial （ In fact, it took a lot more energy than expected ）, Due to limited space , It's all in my GitHub On , Click to get free ！

 Androidndroid Architecture video +BAT Interview topics PDF+ Learning notes

It's easy to be a programmer , To be a good programmer is to keep learning , From junior programmer to senior programmer , From junior architect to senior architect , Or go to management , From technical manager to technical director , Each stage requires different abilities . Set your career direction early , In order to get rid of peers in work and ability improvement .

• No matter how good you are, you must Continuous learning No chicken soup , Others seem effortless , In fact, it took a lot of effort , These four words are my advice ！！
• I hope everyone who works hard to live IT The engineer , Will get what they want , Because we work hard , We deserve it .

It's easy to be a programmer , To be a good programmer is to keep learning , From junior programmer to senior programmer , From junior architect to senior architect , Or go to management , From technical manager to technical director , Each stage requires different abilities . Set your career direction early , In order to get rid of peers in work and ability improvement .

No matter how good you are, you must Continuous learning No chicken soup , Others seem effortless , In fact, it took a lot of effort , No one can succeed at will .

come on. , Mutual encouragement .