keep previously loaded fragment instance when tab changes instead of creating new one in android

Question

I have a tab swiped layout which includes four tabs each of which have their own layout and fragment, in my main activity layout a viewpager takes part for changing tabs. specific view(tab) loads when app starts up and the others will be loaded when the tab changes. my problem is when I nevigate to the third or forth tab (not the second tab) a new instance of it's corresponding fragment will be created instead of loading previously created fragment (the expected behavior that only occur for the second tab).When I navigate to the second tab (SecondPageFragment()) and again come back to first tab it works correct and doesn't create a new IndexFragment, it load the previously created fragment instead so every thing is fine in this case but when I go to the third or forth tab and then come back to first tab it creates an new instance of IndexFragment.

what's the possible reason for that and why it only happens for third,forth etc tab and only second tab works correct and as expected ????

here is my codes that switch the tabs and their corresponding fragments

public class TabsPagerAdapter extends FragmentPagerAdapter {

public TabsPagerAdapter(FragmentManager fm) {
    super(fm);
}

@Override
public Fragment getItem(int index) {

    switch (index) {
    case 0:
        return new ForthPageFragment();

    case 1:
        return new ThirdPageFragment();
    case 2:
        return new SecondPageFragment();
    case 3:
        return new IndexFragment();
        default :
            break;
    }

    return null;
}

@Override
public int getCount() {
    // get item count - equal to number of tabs
    return 4;
}

}

and here is my main activity code :

public class MainActivity extends  FragmentActivity implements
ActionBar.TabListener {
private ViewPager viewPager;
private TabsPagerAdapter mAdapter;
private ActionBar actionBar;
// Tab titles
private String[] tabs = { "صفحه چهارم","صفحه سوم","صفحه دوم","صفحه اصلی" };
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    // Initilization
    viewPager = (ViewPager)findViewById(R.id.tabpager);
    actionBar = getActionBar();
    mAdapter = new TabsPagerAdapter(getSupportFragmentManager());
    viewPager.setAdapter(mAdapter);
    actionBar.setHomeButtonEnabled(false);
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);        
    // Adding Tabs
    for (String tab_name : tabs) {
        actionBar.addTab(actionBar.newTab().setText(tab_name)
                .setTabListener(this));
    }
    viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

        @Override
        public void onPageSelected(int position) {
            // on changing the page
            // make respected tab selected
            actionBar.setSelectedNavigationItem(position);
        }

        @Override
        public void onPageScrolled(int arg0, float arg1, int arg2) {
        }

        @Override
        public void onPageScrollStateChanged(int arg0) {
        }
    });
    viewPager.setCurrentItem(3);
}

@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}

@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
    viewPager.setCurrentItem(tab.getPosition());
}
}

Answer 1

viewPager.setOffscreenPageLimit(3);