Question

Possible Duplicate:
Understand the R class in Android

I cant understand why use ‘R’ Class in android application.

 setContentView(R.layout.main);

Can explain why use R used here.

Answer 1

Your question is duplicate of Understand the R class in Android

When your application is compiled, aapt generates the R class, which
contains resource IDs for all the resources in your res/ directory.
For each type of resource, there is an R subclass (for example,
R.drawable for all drawable resources) and for each resource of that
type, there is a static integer (for example, R.drawable.icon). This
integer is the resource ID that you can use to retrieve your resource.

I got this detail from the below link ,check this once for more details :
http://developer.android.com/guide/topics/resources/accessing-resources.html