Q:

Android AsyncTask with Input and Output not working

I have 2 Classes: a Main Class handling the UI and a second Class for retrieving Data from SQL Server by using PHP.
From the first class a mehtod in the second class is called with passing and retrieving variables. 
Actually it is working fine without AsyncTask.
But since I want to use the code on devices running Android 3.0 and above, I need to change the method to be an AsyncTask. Else I get this error: "android.os.networkonmainthreadexception"
the actual working code Looks like this:
Main class:
...
String inputString="1";
String outputString;
outputString = Class2.SomeMethodInClass2(inputString);   
....

Class2:
public class Class2 {

   public static String SomeMethodInClass2(String input) {
      String Output;
      ...
      //Do some php-sql stuff based on "input"-variable
      //and return the "output"-variable 
      ...
      return output;
   }
}

This code works perfectly on Android 2.0 but I need to change it to AsyncTask, because Andoid 3.0 and above is giving me: "android.os.networkonmainthreadexception"
I have read a lot of threads about AsyncTask, but I can not get it to work with Input and Output in my code.
Eclipse allways tells me there is something wrong with my code.
How do I have to change my code, to be a working async Task? (please explain using my above code sample)
--edit: if there is an easier way to get rid of "android.os.networkonmainthreadexception" on 3.0 an above than AsyncTask, this would be fine too! --

A:

Have a Callback in SecondClass
Extend your SecondClass with Asynctask
Implement preExecute,doinbackground, postExecute methods
Do your stuff in doinbackground
return result in doinbackground
In postExecute pass result to the Callback
Implement SecondClass.Callback in FirstClass
start SecondClass (execute) and pass a Callback reference from FirstClass
In Callback just handle your next operations with the result
EDIT : 
public class SecondClass extends AsyncTask<String, Void, String> {
public interface Callback {
    public void update(String result);
}
Callback mCallback;

    public SecondClass(Callback callback) {
        super();
    mCallback = callback;
    }

    @Override
    protected String doInBackground(String... params) {
    String result = null;
        //do your stuff and save result
        return result;
    }

@Override
    protected void onPostExecute(String result) {
    if(mCallback != null)
    mCallback.update(result)
        super.onPostExecute(e);
    }
}

public class FirstClass implements SecondClass.Callback{
@Override
public void update(String result){
      //do your stuff with result
}

return_type someMethod(){
  SecondClass sc = new SecondClass(this) ;
  sc.execute(someurl);
  }
  }

