What is different between MainActivity.this vs getApplicationContext()

I am trying ProgressDialog. But I am confused.

1. pd=ProgressDialog.show(MainActivity.this, "", "Fething data");

when I do use (MainActivity.this) then it is ok. But

2. pd=ProgressDialog.show(getApplicationContext(), "", "Fething data");

When I do use (getApplicationContext()) it is ERROR.

What is problem for this progressDialog?

What is different between (MainActivity.this) vs (getApplicationContext())

and when I use it the perfect time?

For getApplicationContext() Error is:

04-09 15:05:37.453: E/AndroidRuntime(9980): FATAL EXCEPTION: main
04-09 15:05:37.453: E/AndroidRuntime(9980): android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application
04-09 15:05:37.453: E/AndroidRuntime(9980):     at android.view.ViewRootImpl.setView(ViewRootImpl.java:571)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:246)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:69)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at android.app.Dialog.show(Dialog.java:281)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at android.app.ProgressDialog.show(ProgressDialog.java:116)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at android.app.ProgressDialog.show(ProgressDialog.java:99)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at android.app.ProgressDialog.show(ProgressDialog.java:94)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at com.example.shikkok_services.MainActivity$2.onClick(MainActivity.java:27)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at android.view.View.performClick(View.java:4204)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at android.view.View$PerformClick.run(View.java:17355)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at android.os.Handler.handleCallback(Handler.java:725)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at android.os.Handler.dispatchMessage(Handler.java:92)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at android.os.Looper.loop(Looper.java:137)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at android.app.ActivityThread.main(ActivityThread.java:5041)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at java.lang.reflect.Method.invokeNative(Native Method)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at java.lang.reflect.Method.invoke(Method.java:511)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
04-09 15:05:37.453: E/AndroidRuntime(9980):     at dalvik.system.NativeStart.main(Native Method)

Solution

Which context to use?

There are two types of Context:

Application context is associated with the application and will always be the same throughout the life of application; it does not change. So if you are using Toast, you can use application context or even activity context (both) because Toast can be displayed from anywhere within your application and is not attached to a specific window. But there are many exceptions. One such exception is when you need to use or pass the activity context.

Activity context is associated with the activity and can be destroyed if the activity is destroyed; there may be multiple activities (more than likely) with a single application. Sometimes you absolutely need the activity context handle. For example, should you launch a new Activity, you need to use activity context in its Intent so that the newly-launched activity is connected to the current activity in terms of activity stack. However, you may also use application's context 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.

Let's consider some cases:

MainActivity.this refers to the MainActivity context which extends Activity class but the base class (Activity) also extends Context class, so it can be used to offer activity context.

getBaseContext() offers activity context.

getApplication() offers application context.

getApplicationContext() also offers application context.

For more information please check this link.