Android :: External AsyncTask Class With ProgressDialog

What I want is just to have the AsyncTaskTask showing a progressbar an external class. To do this I am passing the context as you can see in the main class. But whatever I try I get NullPointerException.

Working code examples.

Using Android 2.2 by the way.

main:

CODE:............

Update:
I have a follow up question: Using the above code, is it possible to return a value from the onPostExecute method back to the main class, somehow? (Sorry about beeing noobish)
I have tried something like this:

String result = new AsyncClass(this).execute();

and then a method that return back a string. But I can't do that because i got:

Type mismatch: cannot convert from AsyncTask<String,Void,Void> to String