Difference Between Getcontext() , Getapplicationcontext() , Getbasecontext() and "This"

Difference between getContext() , getApplicationContext() , getBaseContext() and this

• View.getContext(): Returns the context the view is currently running in. Usually the currently active Activity.

• Activity.getApplicationContext(): Returns the context for the entire application (the process all the Activities are running inside
  of). Use this instead of the current Activity context if you need a
  context tied to the lifecycle of the entire application, not just the
  current Activity.

• ContextWrapper.getBaseContext(): If you need access to a Context from within another context, you use a ContextWrapper. The
  Context referred to from inside that ContextWrapper is accessed via
  getBaseContext().

getBaseContext or getContext? How do they differ?

getContext() Returns the context the view is currently running in. . Activity.

getBaseContext() : If you need access to a Context from within another context, you use this

difference and when to use getApplication(), getApplicationContext(), getBaseContext() and someClass.this

Toast and Intent, both requires reference to context. And getApplication, getApplicationContext, LoginActivity.this and getBaseContext, they all offer reference to the context.

Now the thing confuses is the declaration of different contexts and their specific-usage. To make things simple, you should count two types of context available in the Android framework.

1. Application Context
2. Activity Context

Application context is attached to the application's life-cycle and will always be same throughout the life of application. So if you are using Toast, you can use application context or even activity context (both) because a toast can be raised from anywhere with in your application and is not attached to a window.

Activity context is attached to the Activity's life-cycle and can be destroyed if the activity's onDestroy() is raised. If you want to launch a new activity, you must need to use activity's context in its Intent so that the new launching activity is connected to the current activity (in terms of activity stack). However, you may use application's context too to launch a new activity but then you need to set flag Intent.FLAG_ACTIVITY_NEW_TASK in intent to treat it as a new task.

Now referring to your cases:

LoginActivity.this though its referring to your own class which extends Activity class but the base class (Activity) also extends Context class, so it can be used to offer activity context.

getApplication() though its referring to Application object but the Application class extends Context class, so it can be used to offer application context.

getApplicationContext() offers application context.

getBaseContext() offers activity context.

Tips: Whenever you need to manipulate Views then go for
Activity-Context, else Application-Context would be enough.

Difference between getApplicationContext() and this in Android

In the case of an OnClickListener, this is the anonymous class of the OnClickListener, therefore not a Context.

Whereas calling that method works because it's from the Activity class.

Alternatively, MyActivity.this works as well.

getApplicationContext(), getBaseContext(), getApplication(), getParent()

getApplicationContext() Application context is associated with the Application and will always be the same throughout the life cycle.

getBasecontext() should not be used, just use Context instead of it which is associated with the activity and can be destroyed when the activity is destroyed.

Android: why must use getBaseContext() instead of this

1. getApplicationContext () returns the application context of the entire application life cycle,when application will destroy then it will destroy also.

2. this the context returns the current context of the activity, belong to the activity, the activity is destroyed then it will destroy also.but in your case it will refers to the Spinner instance because we are using this within onItemSelected(AdapterView<?>arg0, View arg1, int arg2, long arg3) method which is from Spinner class and Spinner inherit this method from AdapterView.OnItemSelectedListener interface

3. getBaseContext() is the method of ContextWrapper. And ContextWrapper is, "Proxying implementation of Context that simply delegates all of its calls to another Context. Can be subclassed to modify behavior without changing the original Context." (as per javadocs)..

and in your case :Spinner class is not subclass of Context or ContextWrapper class*

Toast.makeText(getBaseContext(),"SELECTED", Toast.LENGTH_SHORT).show();

means getBaseContext() is method of ContextWrapper and ContextWrapper is Proxying implementation of Context so indirectly we are passing an Context Class Object.

or we can also pass 'Activity.this' because Activity class is subclass of ContextWrapper class .

if you go with android documention then this method require an Context class object:

public static Toast makeText (Context context, int resId, int duration)

so we are not able to pass an activity or class context means this to Toast.makeText which don't have a subclass of either Context or ContextWrapper class.

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