android - What exactly does using the Application Context mean?

Question

I'm new to this and I'm sorry if this is a really dumb question. I'm just trying to clarify things. My book says I can retrieve application context for process by using the getApplicationContext() method. I just really don't know where to type this or what to do with any of it. I can go to the hierarchy but what do I do with all the script there. Also where would I write Activity Callbacks, in the main.xml? An exercise wants me to add a logging tag to my project but I'm not sure how to do this. The exact text says:

"Within the onCreate() callback method, add an informational logging message, using the Log.i() method."

and another exercise says to:

"Implement some of the Activity callback methods in addition to onCreate(), such as onStart(). Add a log message to each callback method and then run the application normally".

As these seem like basic questions, can someone please help me.

I am using the Android SDK, and Eclipse. I have made the Hello World application, but I have no idea what to do with Context or Retrieving resources. Please help!

Answer 1

The first rule I would give you: if you don't know why you need it, you probably don't need it. Use your activity object as the Context when you need a context.

The callbacks you talk about are on the Activity class. The Application Fundamentals describes what an Activity is: http://developer.android.com/guide/topics/fundamentals.html#Components

The only time you want to use getApplicationContext() is when you need a Context that exists outside of the lifecycle of an Activity class (or other component). You'll want to find documentation on specific cases where this is desired, there is a lot floating around. For example this one is part of the Android documentation: http://android-developers.blogspot.de/2009/01/avoiding-memory-leaks.html