AsyncTask run in background thread of a invisible Fragment of ViewPager

Further exercise from last post "Communication between Fragments in ViewPager".

When a button in MyFragmentA clicked, it will start a AsyncTask in MyFragmentC, running in background and update a ProgressBar. When the ProgressBar finished, it will update MyFragmentB. It can be noted that the AsyncTask run in background even MyFragmentC is not in visible screen.

Modify MyFragmentA.java and /res/layout/fragment_a.xml to add a Butten to start AsyncTask in MyFragmentC.

package com.exercise.AndroidViewPager;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MyFragmentA extends Fragment {
 
 EditText A_input;
 Button A_enter;
 Button A_startCProgress;

 @Override
 public View onCreateView(LayoutInflater inflater, ViewGroup container,
   Bundle savedInstanceState) {
  View myFragmentView = inflater.inflate(R.layout.fragment_a, container, false);
  
  A_input = (EditText)myFragmentView.findViewById(R.id.a_input);
  A_enter = (Button)myFragmentView.findViewById(R.id.a_enter);
  A_enter.setOnClickListener(A_enterOnClickListener);
  
  A_startCProgress = (Button)myFragmentView.findViewById(R.id.a_startcprogress);
  A_startCProgress.setOnClickListener(A_startCProgressOnClickListener);
  
  return myFragmentView;
 }
 
 OnClickListener A_startCProgressOnClickListener
 = new OnClickListener(){

  @Override
  public void onClick(View v) {
   // TODO Auto-generated method stub
   String TabOfFragmentC = ((AndroidViewPagerActivity)getActivity()).getTabFragmentC();
   
   MyFragmentC fragmentC = (MyFragmentC)getActivity()
     .getSupportFragmentManager()
     .findFragmentByTag(TabOfFragmentC);

   fragmentC.StartProgress();
   
  }
  
 };
 
 OnClickListener A_enterOnClickListener
 = new OnClickListener(){

  @Override
  public void onClick(View arg0) {
   
   String textPassToB = A_input.getText().toString();
   
   String TabOfFragmentB = ((AndroidViewPagerActivity)getActivity()).getTabFragmentB();
   
   MyFragmentB fragmentB = (MyFragmentB)getActivity()
     .getSupportFragmentManager()
     .findFragmentByTag(TabOfFragmentB);

   fragmentB.b_updateText(textPassToB);
   
   Toast.makeText(getActivity(), 
     "text sent to Fragment B:\n " + TabOfFragmentB, 
     Toast.LENGTH_LONG).show();
  }};

}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:orientation="vertical" >
   <TextView
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:text="It's Fragment A" />
   <EditText
       android:id="@+id/a_input"
       android:layout_width="match_parent"
       android:layout_height="wrap_content" />
   <Button
       android:id="@+id/a_enter"
       android:layout_width="match_parent"
       android:layout_height="wrap_content" 
       android:text="Enter to Fragment B"/>
   <Button
       android:id="@+id/a_startcprogress"
       android:layout_width="match_parent"
       android:layout_height="wrap_content" 
       android:text="Start Async Progress in Fragment C"/>
</LinearLayout>

Modify MyFragmentC.java and /res/layout/fragment_c.xml to add a ProgressBar and implement AsyncTask.

package com.exercise.AndroidViewPager;

import android.os.AsyncTask;
import android.os.Bundle;
import android.os.SystemClock;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ProgressBar;

public class MyFragmentC extends Fragment {
 
 ProgressBar cProgress;

 @Override
 public View onCreateView(LayoutInflater inflater, ViewGroup container,
   Bundle savedInstanceState) {
  View myFragmentView = inflater.inflate(R.layout.fragment_c, container, false);
  
  String myTag = getTag();
  ((AndroidViewPagerActivity)getActivity()).setTabFragmentC(myTag);
  
  cProgress = (ProgressBar)myFragmentView.findViewById(R.id.progressbar);
  
  return myFragmentView;
 }
 
 public void StartProgress(){
  new ProgressAsyncTask().execute();
 }
 
 public class ProgressAsyncTask extends 
  AsyncTask<Void, Integer, Void> {

  int myProgress;
  
  @Override
  protected void onPreExecute() {
   // TODO Auto-generated method stub
   super.onPreExecute();
   myProgress = 0;
  }

  @Override
  protected void onPostExecute(Void result) {
   // TODO Auto-generated method stub
   super.onPostExecute(result);
   
   String TabOfFragmentB = ((AndroidViewPagerActivity)getActivity()).getTabFragmentB();
   MyFragmentB fragmentB = (MyFragmentB)getActivity()
     .getSupportFragmentManager()
     .findFragmentByTag(TabOfFragmentB);
   fragmentB.b_updateText("Progress finished!");
   
  }

  @Override
  protected Void doInBackground(Void... arg0) {
   // TODO Auto-generated method stub
   while(myProgress<100){
    myProgress++;
    publishProgress(myProgress);
     SystemClock.sleep(100);  
   }
   return null;
  }

  @Override
  protected void onProgressUpdate(Integer... values) {
   // TODO Auto-generated method stub
   cProgress.setProgress(values[0]);
  }
  
 }

}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:orientation="vertical" >
   <TextView
       android:layout_width="match_parent"
       android:layout_height="wrap_content"
       android:text="It's Fragment C" />
 <ProgressBar
     android:id="@+id/progressbar"
     android:layout_width="fill_parent"
     android:layout_height="wrap_content"
     style="?android:attr/progressBarStyleHorizontal"
     android:progress="0"
     android:max="100"/>
</LinearLayout>

main activity, AndroidViewPagerActivity.java

package com.exercise.AndroidViewPager;

import java.util.ArrayList;

import android.app.ActionBar;
import android.app.ActionBar.Tab;
import android.app.FragmentTransaction;
import android.content.Context;
import android.os.Bundle;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;

public class AndroidViewPagerActivity extends FragmentActivity {
 
 ViewPager mViewPager;
 TabsAdapter mTabsAdapter;
 
 String TabFragmentB;
 String TabFragmentC;
 
 public void setTabFragmentB(String t){
  TabFragmentB = t;
 }
 
 public String getTabFragmentB(){
  return TabFragmentB;
 }
 
 public void setTabFragmentC(String t){
  TabFragmentC = t;
 }
 
 public String getTabFragmentC(){
  return TabFragmentC;
 }
 
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        mViewPager = new ViewPager(this);
        mViewPager.setId(R.id.pager);
        setContentView(mViewPager);
        
        final ActionBar bar = getActionBar();
        bar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        bar.setDisplayOptions(0, ActionBar.DISPLAY_SHOW_TITLE);
        
        mTabsAdapter = new TabsAdapter(this, mViewPager);
        mTabsAdapter.addTab(bar.newTab().setText("Fragment A"),
                MyFragmentA.class, null);
        mTabsAdapter.addTab(bar.newTab().setText("Fragment B"),
          MyFragmentB.class, null);
        mTabsAdapter.addTab(bar.newTab().setText("Fragment C"),
          MyFragmentC.class, null);

        if (savedInstanceState != null) {
            bar.setSelectedNavigationItem(savedInstanceState.getInt("tab", 0));
        }

    }

 @Override
 protected void onSaveInstanceState(Bundle outState) {
  //super.onSaveInstanceState(outState);
  outState.putInt("tab", getActionBar().getSelectedNavigationIndex());
 }
 
 public static class TabsAdapter extends FragmentPagerAdapter
  implements ActionBar.TabListener, ViewPager.OnPageChangeListener {
  
  private final Context mContext;
        private final ActionBar mActionBar;
        private final ViewPager mViewPager;
        private final ArrayList<TabInfo> mTabs = new ArrayList<TabInfo>();
        
        static final class TabInfo {
            private final Class<?> clss;
            private final Bundle args;

            TabInfo(Class<?> _class, Bundle _args) {
                clss = _class;
                args = _args;
            }
        }

  public TabsAdapter(FragmentActivity activity, ViewPager pager) {
   super(activity.getSupportFragmentManager());
            mContext = activity;
            mActionBar = activity.getActionBar();
            mViewPager = pager;
            mViewPager.setAdapter(this);
            mViewPager.setOnPageChangeListener(this);
        }

  public void addTab(ActionBar.Tab tab, Class<?> clss, Bundle args) {
            TabInfo info = new TabInfo(clss, args);
            tab.setTag(info);
            tab.setTabListener(this);
            mTabs.add(info);
            mActionBar.addTab(tab);
            notifyDataSetChanged();
        }

  @Override
  public void onPageScrollStateChanged(int state) {
   // TODO Auto-generated method stub
   
  }

  @Override
  public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
   // TODO Auto-generated method stub
   
  }

  @Override
  public void onPageSelected(int position) {
   // TODO Auto-generated method stub
   mActionBar.setSelectedNavigationItem(position);
  }

  @Override
  public void onTabReselected(Tab tab, FragmentTransaction ft) {
   // TODO Auto-generated method stub
   
  }

  @Override
  public void onTabSelected(Tab tab, FragmentTransaction ft) {
   Object tag = tab.getTag();
            for (int i=0; i<mTabs.size(); i++) {
                if (mTabs.get(i) == tag) {
                    mViewPager.setCurrentItem(i);
                }
            }
  }

  @Override
  public void onTabUnselected(Tab tab, FragmentTransaction ft) {
   // TODO Auto-generated method stub
   
  }

  @Override
  public Fragment getItem(int position) {
   TabInfo info = mTabs.get(position);
            return Fragment.instantiate(mContext, info.clss.getName(), info.args);
  }

  @Override
  public int getCount() {
   return mTabs.size();
  }

 }

}

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