What is a context on Android?

Question

What is a context on Android?

What’s the difference between getContext(), getApplicationContext(), getBaseContext()?

Has some relationship with getActivity?

Answer 1

(References: official documentation and two questions soen.)

Context

It is an access point for global information about a application environment. This is an abstract class whose implementation is provided by Android system. It allows access to features and application-specific classes, as well as calls to Application-level operations how to start activities, send or receive intents for broadcast, etc..

In other words, Context is the way provided by the system for your application to access certain features (such as the start feature of a Activity, start or stop a service, send a broadcast, open a database or preferences file, etc.) or classes (like the various Managers the system offers: Telephony, Alarm, Sensors, Audio, Notifications, Power, USB, etc.). These features and classes have the particularity of being global at the application level, that is, they are application-level. It is still a God Object as says the Square - and, indeed, without an instance of Context you don’t do much in an Android app.

Application

Base class for those who need to preserve global application status. You can provide your own implementation (usually there is no need, and static singletons can provide the same functionality in a more modular way).

Activity

An Activity is a unique and focused thing that the user can do.

Service

It is an application component that can either represent an application’s desire to run a longer operation while avoiding interacting with the user or providing functionality for other applications to use.

Application, Activity and Service are achievements of Context, that is, concrete classes that implement a Context Android. When you extend these classes into your code, you have access to the application-level services provided by Context inherited by these classes. In addition, you have access to resources specific to each subclass; for example, to Activity active at the moment can be closed through the method finish() and can execute code on the main thread in a simple way through the method runOnUiThread(). Activities, Services and Applications have each their particular life cycle. And not always the contexts are interchangeable; for example, if you try to display a Dialog passing to him a context Application, this will cause an error due to Android waiting for it to be passed a Activity (this particular problem is more of an Android idiosyncrasy, which should expect to receive soon a Activity).

Differences between the methods

• View.getContext(): Returns the context in which the view is being displayed. Generally the Activity active at the moment.

• Activity.getApplicationContext(): Returns the context of the entire application (the process within which all Activities are being performed). Use this in place of the current active Activity context if you are in need of a context linked to the entire application lifecycle.

• ContextWrapper.getBaseContext(): It’s a class method ContextWrapper. And ContextWrapper is "an implementation proxy of Context that simply delegates all your calls to another Context. Can be extended to modify behaviors without changing the Context original."

• Fragment.getActivity(): Returns to Activity to which this fragment is attached. A fragment does not have Context by itself; but when it is connected (Attached or Added) to a Activity has access to the context of Activity, or an instance of Application has access to that instance even if it is disconnected from Activity.

Answer 2

As the name suggests, it is the context of the object or application. It is a way to access in the code the current state of the application.

On Android, Context is the base class for Activity, Service, Application, therefore, it is a way to access and deal with your application via code.