Making asynctasks rotation proof

package com.mango.rotationproof;

import android.app.Activity;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

/**
 * Created by Avinash on 21-05-2015.
 */
public class TaskFrag extends Fragment {
    MyTask myTask;
    Activity activity;
    public TaskFrag()
    {

    }
    public void begintask()
    {
        myTask=new MyTask(activity);
        myTask.execute();

    }
    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        setRetainInstance(true);
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);
        this.activity=activity;
        if(myTask!=null)
        {
            myTask.onAttach(activity);
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        if(myTask!=null) {
            myTask.onDetach();
        }
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return null;
    }
}

package com.mango.rotationproof;

import android.app.Activity;
import android.os.AsyncTask;

/**
 * Created by Avinash on 21-05-2015.
 */
public class MyTask extends AsyncTask<Void,Void,Void>{
    Activity activity;

    public MyTask(Activity activity)
    {
        onAttach(activity);
    }

    public void onAttach(Activity activity)
    {
        this.activity=activity;
    }

    public void onDetach()
    {
        activity=null;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        ((MainActivity)activity).showpb();
        ((MainActivity)activity).hideres();

    }

    @Override
    protected Void doInBackground(Void... params) {
        try {
            Thread.currentThread().sleep(4000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
        ((MainActivity)activity).hidepb();
        ((MainActivity)activity).showres();

    }
}

 

package com.mango.rotationproof;

import android.os.AsyncTask;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;


public class MainActivity extends ActionBarActivity {
    Button btn;
    TextView tv;
    ProgressBar pb;
    TaskFrag frag;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn = (Button) findViewById(R.id.btn);
        tv = (TextView) findViewById(R.id.tv);
        pb = (ProgressBar) findViewById(R.id.pb);

        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                frag.begintask();
            }
        });
        if(savedInstanceState==null)
        {
            frag=new TaskFrag();
            getSupportFragmentManager().beginTransaction().add(frag,"tag").commit();
        }
        else
        {
            frag= (TaskFrag) getSupportFragmentManager().findFragmentByTag("tag");
            showpb();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }



    public void showpb()
    {   if(frag.myTask!=null){
        if(pb.getVisibility()!=View.VISIBLE)
        {
            pb.setVisibility(View.VISIBLE);
        }}
    }

    public void hidepb()
    {   if(frag.myTask!=null){
        if(pb.getVisibility()!=View.GONE)
        {
            pb.setVisibility(View.GONE);
        }}
    }
    public void showres()
    {if(frag.myTask!=null){
        if(tv.getVisibility()!=View.VISIBLE)
        {
            tv.setVisibility(View.VISIBLE);
        }}
    }
    public void hideres()
    {if(frag.myTask!=null){
        if(tv.getVisibility()!=View.GONE)
        {
            tv.setVisibility(View.GONE);
        }}
    }
}