What is Context on Android

Question

In Android programming  what exactly is a Context class and what is it used for   I read about it on the developer site  but I am unable to understand it clearly

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This attribute declares which activity this layout is associated with by default

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If you want to connect Context with other familiar classes in Android  keep in mind this structure      Context  lt  ContextWrapper  lt  Application      Context  lt  ContextWrapper  lt  ContextThemeWrapper  lt  Activity      Context  lt  ContextWrapper  lt  ContextThemeWrapper  lt  Activity  lt    ListActivity      Context  lt  ContextWrapper  lt  Service      Context  lt  ContextWrapper  lt  Service  lt  IntentService   So  all of those classes are contexts in their own way  You can cast Service and ListActivity to Context if you wish  But if you look closely  some of the classes inherit theme as well  In activity or fragment  you would like theming to be applied to your views  but don t care about it Service class  for instance   I explain the difference in contexts here

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The Context is the android specific api to each app-s Sandbox that provides access app private data like to resources  database  private filedirectories  preferences  settings       Most of the privatedata are the same for all activities services broadcastlisteners of one application   Since Application  Activity  Service implement the Context interface they can be used where an api call needs a Context parameter

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An Android Context is an Interface  in the general sense  not in the Java sense  in Java  Context is actually an abstract class   that allows access to application specific resources and class and information about application environment   If your android app was a web app  your context would be something similar to ServletContext  I am not making an exact comparison here    Your activities and services also extend Context  so they inherit all those methods to access the environment information in which the app is running

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Context is an interface to global information about an application environment  It s an abstract class whose implementation is provided by the Android system   Context allows access to application-specific resources and classes  as well as calls for application-level operations such as launching activities  broadcasting and receiving intents  etc   Here is Example   public class MyActivity extends Activity          public void Testing            Context actContext   this    returns the Activity Context since   Activity extends Context           Context appContext   getApplicationContext         returns the context of the single  global Application object of the current process            Button BtnShowAct1    Button  findViewById R id btnGoToAct1         Context BtnContext   BtnShowAct1 getContext        returns the context of the View       For more details you can visit http   developer android com reference android content Context html

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Just putting it out there for newbies   So First understand Word Context    In english-lib  it means       The circumstances that form the setting for an event  statement  or   idea  and in terms of which it can be fully understood and assessed         The parts of something written or spoken that immediately precede and   follow a word or passage and clarify its meaning     Now take the same understanding to programming world   context of current state of the application object  It lets newly created objects understand what has been going on  Typically you call it to get information regarding another part of your program  activity  package application   You can get the context by invoking getApplicationContext    getContext    getBaseContext   or this  when in the activity class    To Get Context Anywhere in application use following code   Create new class AppContext inside your android application   public class AppContext extends Application        private static Context context       public void onCreate            super onCreate            AppContext context   getApplicationContext               public static Context getAppContext             return AppContext context            Now any time you want application context in non-activity class  call this method and you have application context    Hope this help

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Putting it simply   As the name suggests  it s the context of current state of the application object  It lets newly-created objects understand what has been going on  Typically you call it to get information regarding another part of your program  activity and package application    You can get the context by invoking getApplicationContext    getContext    getBaseContext   or this  when in a class that extends from Context  such as the Application  Activity  Service and IntentService classes    Typical uses of context    Creating new objects  Creating new views  adapters  listeners   TextView tv   new TextView getContext     ListAdapter adapter   new SimpleCursorAdapter getApplicationContext           Accessing standard common resources  Services like LAYOUT INFLATER SERVICE  SharedPreferences   context getSystemService LAYOUT INFLATER SERVICE  getApplicationContext   getSharedPreferences  name    mode     Accessing components implicitly  Regarding content providers  broadcasts  intent  getApplicationContext   getContentResolver   query uri

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The class android content Context provides the connection to the Android system and the resources of the project  It is the interface to global information about the application environment    The Context also provides access to Android Services  e g  the Location Service    Activities and Services extend the Context class

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Context is Instances of the the class android content Context provide the connection to the Android system which executes the application  For example  you can check the size of the current device display via the Context   It also gives access to the resources of the project  It is the interface to global information about the application environment   The Context class also provides access to Android services  e g   the alarm manager to trigger time based events   Activities and services extend the Context class  Therefore they can be directly used to access the Context

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Context is a reference to the current object as this  Also context allows access to information about the application environment

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Think of it as the VM that has siloed the process the app or service is running in   The siloed environment has access to a bunch of underlying system information and certain permitted resources   You need that context to get at those services

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for more details about context  read this article  I will explain that briefly  If you wanna know what is context you must know what it does    for example getContext   is one of the methods that retrieve context  In getContext    Context is tied to an Activity and its lifecycle  We can imagine Context as layer which stands behind Activity and it will live as long as Activity lives  The moment the Activity dies  Context will too  this method gives list of functionalities to activity  like  Load Resource Values  Layout Inflation  Start an Activity  Show a Dialog  Start a Service  Bind to a Service  Send a Broadcast  Register BroadcastReceiver   now imagine that    Context is a layer interface  which stands behind its component  Activity  Application     and component   s lifecycle  which provides access to various functionalities which are supported by application environment and Android framework

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Simple Example to understand context in android   Every boss has an assistant to look after  to do all less important and time-consuming tasks  If a file or a cup of coffee is needed  an assistant is on the run  Some bosses barely know what   s going on in the office  so they ask their assistants regarding this too  They do some work themselves but for most other things they need the help of their assistants  In this scenario  Boss      is the Android application Assistant     is a context Files Cup of coffee      are resources We generally call context when we need to get information about different parts of our application like Activities  Applications  etc  Some operations things where the assistant is needed  where context is involved   Loading common resources Creating dynamic views Displaying Toast messages Launching Activities etc   Different ways of getting context  getContext    getBaseContext    getApplicationContext    this

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Context is an  interface  to the global information about an application environment  In practice  Context is actually an abstract class  whose implementation is provided by the Android system    It allows access to application-specific resources and classes  as well as up-calls for application-level operations  such as launching activities  broadcasting and receiving intents  etc   In the following picture  you can see a hierarchy of classes  where Context is the root class of this hierarchy  In particular  it s worth emphasizing that Activity is a descendant of Context

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Context is basically for resource access and getting the environment details of the application for application context  or activity  for activity context  or any other     In order to avoid memory leak you should use application context for every components that needs a context object     for more click here

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Boss Assistant Analogy  Let s have a small analogy before diving deep in the technicality of Context     Every Boss has an assistant or someone  errand boy  who does less   important and more time-consuming things for him  For example  if they   need a file or coffee then an assistant will be on run  Boss will not   know what is going on in the background but the file or the task will   be delivered      So Here     Boss - Android Application      Assistant - Context   File or       cup of coffee -   Resource   What official Android Developer site says about Context  Context is your access point for application-related resources   Let s see some of such resources or tasks    Launching an activity  Getting an absolute path to the application-specific cache directory on the filesystem  Determining whether the given permission is allowed for a particular process and user ID running in the system  Checking whether you have been granted a particular permission    And so on  So if an Android application wants to start an activity  it goes straight to Context  Access Point   and the Context class gives him back the resources Intent in this case               Like any other class Context class has fields and methods  You can explore more about Context in official documentation  it covers pretty much everything  available methods  fields  and even how to use fields with methods

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Putting simple  Androids Context is a mess that you won t love until you stop worrying about    Android Contexts are    God-objects  Thing that you want to pass around all your application when you are starting developing for Android  but will avoid doing it when you get a little bit closer to programming  testing and Android itself    Unclear dependency  Common source of memory leaks  PITA for testing   Actual context used by Android system to dispatch permissions  resources  preferences  services  broadcasts  styles  showing dialogs and inflating layout  And you need different Context instances for some separate things  obviously  you can t show a dialog from an application or service context  layouts inflated from application and activity contexts may differ

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Context means component  or application  in various time-period  If I do eat so much food between 1 to 2 pm then my context of that time is used to access all methods  or resources  that I use during that time  Content is a component  application  for a particular time  The Context of components of the application keeps changing based on the underlying lifecycle of the components or application  For instance  inside the onCreate   of an Activity    getBaseContext   -- gives the context of the Activity that is set  created  by the constructor of activity   getApplicationContext   -- gives the Context setup  created  during the creation of application    Note   lt application gt  holds all Android Components     lt application gt       lt activity gt      lt  activity gt         lt service gt       lt  service gt        lt receiver gt      lt  receiver gt        lt provider gt      lt  provider gt   lt  application gt     It means  when you call getApplicationContext   from inside whatever component  you are calling the common context of the whole application    Context keeps being modified by the system based on the lifecycle of components

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Source    The topic of Context in Android seems to be confusing to many  People just know that Context is needed quite often to do basic things in Android  People sometimes panic because they try to do perform some operation that requires the Context and they don   t know how to    get    the right Context  I   m going to try to demystify the idea of Context in Android  A full treatment of the issue is beyond the scope of this post  but I   ll try to give a general overview so that you have a sense of what Context is and how to use it  To understand what Context is  let   s take a look at the source code    https   github com android platform frameworks base blob master core java android content Context java  What exactly is Context    Well  the documentation itself provides a rather straightforward explanation  The Context class is an    Interface to global information about an application environment     The Context class itself is declared as an abstract class  whose implementation is provided by the Android OS  The documentation further provides that Context       allows access to application-specific resources and classes  as well as up-calls for application-level operations such as launching activities  broadcasting and receiving intents  etc     You can understand very well  now  why the name is Context  It   s because it   s just that  The Context provides the link or hook  if you will  for an Activity  Service  or any other component  thereby linking it to the system  enabling access to the global application environment   In other words  the Context provides the answer to the components question of    where the hell am I in relation to app generally and how do I access communicate with the rest of the app     If this all seems a bit confusing  a quick look at the methods exposed by the Context class provides some further clues about its true nature    Here   s a random sampling of those methods     getAssets    getResources   getPackageManager   getString   getSharedPrefsFile     What do all these methods have in common  They all enable whoever has access to the Context to be able to access application-wide resources   Context  in other words  hooks the component that has a reference to it to the rest of the application environment  The assets  think     assets    folder in your project   for example  are available across the application  provided that an Activity  Service  or whatever knows how to access those resources   The same goes for getResources   which allows us to do things like getResources   getColor   which will hook you into the colors xml resource  nevermind that aapt enables access to resources via java code  that   s a separate issue     The upshot is that Context is what enables access to system resources and its what hook components into the    greater app   Let   s look at the subclasses of Context  the classes that provide the implementation of the abstract Context class   The most obvious class is the Activity class  Activity inherits from ContextThemeWrapper  which inherits from ContextWrapper  which inherits from Context itself   Those classes are useful to look at to understand things at a deeper level  but for now  it   s sufficient to know that ContextThemeWrapper and ContextWrapper are pretty much what they sound like  They implement the abstract elements of the Context class itself by    wrapping    a context  the actual context  and delegating those functions to that context   An example is helpful - in the ContextWrapper class  the abstract method getAssets from the Context class is implemented as follows    Override     public AssetManager getAssets             return mBase getAssets            mBase is simply a fieldset by the constructor to a specific context  So a context is wrapped and the ContextWrapper delegates its implementation of the getAssets method to that context  Let   s get back to examining the Activity class which ultimately inherits from Context to see how this all works    You probably know what an Activity is  but to review - it   s basically  a single thing the user can do  It takes care of providing a window in which to place the UI that the user interacts with   Developers familiar with other APIs and even non-developers might think of it vernacularly as a    screen     That   s technically inaccurate  but it doesn   t matter for our purposes  So how do Activity and Context interact and what exactly is going in their inheritance relationship    Again  it   s helpful to look at specific examples  We all know how to launch Activities  Provided you have    the context    from which you are starting the Activity  you simply call startActivity intent   where the Intent describes the context from which you are starting an Activity and the Activity you   d like to start  This is the familiar startActivity this  SomeOtherActivity class     And what is this  this is your Activity because the Activity class inherits from Context  The full scoop is like this  When you call startActivity  ultimately the Activity class executes something like this   Instrumentation ActivityResult ar                   mInstrumentation execStartActivity                      this  mMainThread getApplicationThread    mToken  this                      intent  requestCode     So it utilizes the execStartActivity from the Instrumentation class  actually from an inner class in Instrumentation called ActivityResult    At this point  we are beginning to get a peek at the system internals   This is where OS actually handles everything  So how does Instrumentation start the Activity exactly  Well  the param this in the execStartActivity method above is your Activity  i e  the Context  and the execStartActivity makes use of this context    A 30 000 overview is this  the Instrumentation class keeps tracks of a list of Activities that it   s monitoring in order to do its work  This list is used to coordinate all of the activities and make sure everything runs smoothly in managing the flow of activities   There are some operations that I haven   t fully looked into which coordinate thread and process issues  Ultimately  the ActivityResult uses a native operation - ActivityManagerNative getDefault   startActivity   which uses the Context that you passed in when you called startActivity  The context you passed in is used to assist in    intent resolution    if needed  Intent resolution is the process by which the system can determine the target of the intent if it is not supplied   Check out the guide here for more details    And in order for Android to do this  it needs access to information that is supplied by Context  Specifically  the system needs to access to a ContentResolver so it can    determine the MIME type of the intent   s data    This whole bit about how startActivity makes use of context was a bit complicated and I don   t fully understand the internals myself  My main point was just to illustrate how application-wide resources need to be accessed in order to perform many of the operations that are essential to an app  Context is what provides access to these resources   A simpler example might be Views  We all know what you create a custom View by extending  RelativeLayout or some other View class  you must provide a constructor that takes a Context as an argument  When you instantiate your custom View you pass in the context   Why  Because the View needs to be able to have access to themes  resources  and other View configuration details  View configuration is actually a great example  Each Context has various parameters  fields in Context   s implementations  that are set by the OS itself for things like the dimension or density of the display  It   s easy to see why this information is important for setting up Views  etc   One final word   For some reason  people new to Android  and even people not so new  seem to completely forget about object-oriented programming when it comes to Android  For some reason  people try to bend their Android development to pre-conceived paradigms or learned behaviors    Android has it   s own paradigm and a certain pattern that is actually quite consistent if let go of your preconceived notions and simply read the documentation and dev guide  My real point  however  while    getting the right context    can sometimes be tricky  people unjustifiably panic because they run into a situation where they need the context and think they don   t have it  Once again  Java is an object-oriented language with an inheritance design   You only    have    the context inside of your Activity because your activity itself inherits from Context  There   s no magic to it  except for all the stuff the OS does by itself to set various parameters and to correctly    configure    your context   So  putting memory performance issues aside  e g  holding references to context when you don   t need to or doing it in a way that has negative consequences on memory  etc   Context is an object like any other and it can be passed around just like any POJO  Plain Old Java Object    Sometimes you might need to do clever things to retrieve that context  but any regular Java class that extends from nothing other than Object itself can be written in a way that has access to context  simply expose a public method that takes a context and then uses it in that class as needed  This was not intended as an exhaustive treatment on Context or Android internals  but I hope it   s helpful in demystifying Context a little bit

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What s Context exactly      Per the Android reference documentation  it s an entity that represents various environment data  It provides access to local files  databases  class loaders associated to the environment  services  including system-level services   and more  Throughout this book  and in your day-to-day coding with Android  you ll see the Context passed around frequently     From the  Android in Practice  book  p  60   Several Android APIs require a Context as parameter  If you look through the various Android APIs  you   ll notice that many of them take an android content Context object as a parameter  You   ll also see that an Activity or a Service is usually used as a Context  This works because both of these classes extend from Context

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A Context is what most of us would call Application  It s made by the Android system and is able to do only what an application is able to  In Tomcat  a Context is also what I would call an application   There is one Context that holds many Activities  each Activity may have many Views   Obviously  some will say that it doesn t fit because of this or that and they are probably right  but saying that a Context is your current application will help you to understand what you are putting in method parameters

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Definition of Context  Context represents environment data It provides access to things such as databases  Simpler terms  example 1   Consider Person-X is the CEO of a start-up software company   There is a lead architect present in the company  this lead architect does all the work in the company which involves such as database  UI etc   Now the CEO Hires a new Developer   It is the Architect who tells the responsibility of the newly hired person based on the skills of the new person that whether he will work on Database or UI etc    Simpler terms  example 2   It s like access to android activity to the app s resource   It s similar to when you visit a hotel  you want breakfast  lunch  amp  dinner in the suitable timings  right   There are many other things you like during the time of stay  How do you get these things   You ask the room-service person to bring these things for you   Here the room-service person is the context considering you are the single activity and the hotel to be your app  finally the breakfast  lunch  amp  dinner has to be the resources     Things that involve context are   Loading a resource  Launching a new activity  Creating views  obtaining system service    Context is the base class for Activity  Service  Application  etc Another way to describe this  Consider context as remote of a TV  amp  channel s in the television are resources  services  using intents  etc - - - Here remote acts as an access to get access to all the different resources into the foreground   So  Remote has access to channels such as resources  services  using intents  etc       Likewise     Whoever has access to remote naturally has access to all the things such as resources  services  using intents  etc    Different methods by which you can get context  getApplicationContext   getContext   getBaseContext   or this  when in the activity class    Example  TextView tv   new TextView this    The keyword this refers to the context of the current activity

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Context means Android get to know in which activity I should go for or act in   1 - Toast makeText context   Enter All Details   Toast LENGTH SHORT  show    it used in this  Context context   ActivityName this   2 -startActivity new Intent context LoginActivity class     in this context means from which activity you wanna go to other activity  context or ActivityName this is faster then   getContext and getApplicatinContext

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Think of Context as a box with different resources  string  colors  and fonts  If you need a resource  you turn to this box  When you rotate the screen  this box changes because the orientation changes to landscape

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In Java  we say this keyword refers to the state of the current object of the application    Similarly  in an alternate we have Context in Android Development   This can be defined either explicitly or implicitly   Context con   this   getApplicationContext     getBaseContext     getContext

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nbsp Context means current  Context use to do operation for current screen  ex    nbsp  1  getApplicationContext     nbsp  2  getContext    Toast makeText getApplicationContext     hello   Toast LENGTH SHORT  show

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Context  is context of current state of the application object Its an entity that represents various environment data   Context helps the current activity to interact with out side android environment like  local files  databases  class loaders associated to the environment  services including system-level services  and more   A Context is a handle to the system   It provides services like resolving resources  obtaining access to databases and preferences  and so on  An android app has activities  It   s like a handle to the environment your application is currently running in  The activity object inherits the Context object   Different invoking methods by which you can get context 1  getApplicationContext    2   getContext    3  getBaseContext   4  or this  when in the activity class

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Context represents a handle to get environment data   Context class itself is declared as abstract  whose implementation is provided by the android OS  Context is like remote of a TV  amp  channel s in the television are resources  services  etc     What can you do with it     Loading resource  Launching a new activity  Creating views  Obtaining system service    Ways to get context     getApplicationContext   getContext   getBaseContext

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A Context is a handle to the system  it provides services like resolving resources  obtaining access to databases and preferences  and so on  An Android app has activities  Context is like a handle to the environment your application is currently running in  The activity object inherits the Context object   For more information  look in Introduction to Android development with Android Studio - Tutorial

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Instances of the the class android content Context provide the connection to the Android system which executes the application  For example  you can check the size of the current device display via the Context   It also gives access to the resources of the project  It is the interface to global information about the application environment   The Context class also provides access to Android services  e g   the alarm manager to trigger time based events   Activities and services extend the Context class  Therefore they can be directly used to access the Context

[android] What is 'Context' on Android?

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