Unit - 1 Application Context

Lesson Plan: Unit - 01
Subject: P15A2AAD - Android Application Development
Topic of Study: Application Context
Grade/Level: Master of Computer Applications
Objective: To explore the mechanism of Application Context
Time Allotment: 55 Minutes

• Context 
• An Android Context is an Interface (In Java, Context is actually an abstract class) that allows access to application specific resources and class and information about application environment.
• Context is the base class for Activity, Service, Application, 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);
• this -> refers to the context of the current activity.
• Context  is context of current state of the application/object.
• It allows access to application-specific resources and classes.
• It is use for application-level operations such as launching activities, broadcasting and receiving intents, loading resources, launching a new Activity, obtaining a system service, getting internal file paths etc. 

• Context used in android application development everywhere.
• So, take care the wrong use of it leads to memory leaks in the application.

• Ways to get Context:
• view.getContext():
• It's the activity context which the view is hosted.
• Activity.getApplicationContext():
• Exa.: Context con = getApplicationContext();
• get the current application context, when we need context, this global context need to be consider at first.
• Toast can use ApplicationContext.

• Types of Context...
• Activity/Service Context 
• Each Activity or Service, and their corresponding base context are unique per-instance.
• It is refers to the application level environment.
• This context is available in an activity / service. 
• This context is tied to the life cycle of an activity or a service. 
• Example: If you have to create an object whose life cycle is attached to an activity / service, you can use the activity/service context.

• Application Context 
• Application – is a singleton instance running in your application process.  
• It can be accessed via methods like getApplication() from an Activity or Service, and getApplicationContext() from any other object that inherits from Context.  

• Difference between getApplication() and getApplicationContext()
• Android OS has main four components including Activity, Service, Content Provider and Broadcast receiver.
• Actually both functions return application object since application itself is a context. 
• So why android provide two functions? 
• The reason is because getApplication() is only able to be used in Activity and Service. 
• In other components like BroadcastReceiver is only able to use getApplicationContext() to get application object.