[Android] What is Context? ??

Introduction

I researched and learned about Context in my own way, so I will leave it in the article.

As a trigger When I was developing Android and passed Context as a method argument without thinking about anything, I received such a review from a lead engineer.

Be careful of overdose of Context. Before I knew it, I couldn't get out of it and eventually I couldn't touch it. If you add Context to the argument, you should be aware that you will lose and do not add Context to the argument.

So I wondered "What is Context?" And researched various things.

What is Context in the first place? ??

Meaningful Context in Japanese

(Sentence) context, context, context, background, situation, environment

And so on

Context in programming

Excerpt from this site http://e-words.jp/w/%E3%82%B3%E3%83%B3%E3%83%86%E3%82%AD%E3%82%B9%E3%83%88.html

Even in the field of programming, the same code description and program elements may behave differently or be subject to different restrictions depending on their position in the program and the internal state when they are executed. It is sometimes called a context.

Context in Android development

Class definition and inheritance relationship

--Context is defined in an abstract class --Activity superclass (Activity inherits Context class) --Inheritance: Context ← ContextWrapper ← ContextThemeWrapper ← Activity --Application superclass (Application inherits from Context class) --Inheritance: Context ← ContextWrapper ← Application

By the way, getApplicationContext () is defined in ContextWrapper class

When to appear and use

--When Dialog is generated --When using Intent --When accessing application resources (eg getString ())

And so on ... Anyway

Apparently there are two types of Contexts (there are others, but they are omitted this time).

Activity Context

--Depends on the activity life cycle. Therefore, when Activity is destroyed (such as when the screen is rotated), Context is also destroyed. --The instance doesn't seem to be a singleton.

Acquisition method

• Java

  • Activity: this
  • View, Fragment: getContext(), requireContext()

• Kotlin

  • Activity: this
  • View, Fragment: context, requireContext()

Difference between getContext () and requireContext ()

--getContext (): Returns a nullable Context (treated as Context? In Kotlin) as a value --requireContext (): Returns a non-null Context as a value

Reference material

• https://stackoverflow.com/questions/60402490/difference-between-getcontext-and-requirecontext-when-using-fragments
• https://developer.android.com/kotlin/common-patterns?hl=ja

Application Context

--It is application related and does not depend on the activity life cycle. --It will not be destroyed or modified while the application is alive as a singleton.

Acquisition method

Java: getApplicationContext() Kotlin: applicationContext

How is it desirable to use them properly?

In conclusion, it has become an abstract one, "** Implement after considering the life cycle and the risk of memory leaks **".

However, basically, it seems better to use ActivityContext as much as possible in consideration of the risk of memory leak. I referred to multiple articles, but there were various opinions.

Notes on handling Context about memory leak

--If the lifetime of the Context is longer than the lifetime of the receiving object: preferred implementation --If the life of the receiving object is longer than the life of the Context: There is a risk of memory leak

So what if you come across Context in the future?

Until now, I used Context appropriately without thinking about anything, but in this situation, "Which is better to use, ActivityContext or ApplicationContext?” I will implement it while thinking. We will deepen our understanding in that.

• Currently, there may be various omissions due to lack of ability of myself. I will devote myself.

Special Thanks (reference material)

• https://qiita.com/iduchikun/items/34b3ae26cfc438e7e5dc
• https://tech.ga-tech.co.jp/entry/2020/06/android-contexts
• https://www.lanches.co.jp/blog/9776
• https://developer.android.com/reference/android/content/Context?hl=ja
• http://mitoroid.com/category/android/android_context.php
• https://qiita.com/k-yamada-github/items/bd99f45ed0d7176d2612
• https://qiita.com/roba4coding/items/0585b8240873ec5e9c20
• https://blog.meilcli.net/2018/12/26/185752
• https://blog.meilcli.net/2018/12/26/185752

Finally

If you have any mistakes or suggestions, please feel free to comment!

Finally, in conclusion, Context is difficult ... Thank you very much.