How to handle AsyncTask's in ActionBarActivity Fragments when ViewPager is used?

The FragmentPagerAdapter keeps additional fragments, besides the one shown, in resumed state. The solution is to implement a custom OnPageChangeListener and create a new method for when the fragment is shown.

1) Create LifecycleManager InterfaceThe interface will have two methods and each ViewPager’s Fragment will implement it. These methods Are as follows:

public interface FragmentLifecycle {    public void onPauseFragment();    public void onResumeFragment();}

2) Let each Fragment implement the interfaceAdd iplements statement for each class declaration:

public class FragmentBlue extends Fragment implements FragmentLifecyclepublic class FragmentGreen extends Fragment implements FragmentLifecyclepublic class FragmentPink extends Fragment implements FragmentLifecycle

3) Implement interface methods in each fragmentIn order to check that it really works as expected, I will just log the method call and show Toast:

@Overridepublic void onPauseFragment() {    Log.i(TAG, "onPauseFragment()");    Toast.makeText(getActivity(), "onPauseFragment():" + TAG, Toast.LENGTH_SHORT).show(); }@Overridepublic void onResumeFragment() {    Log.i(TAG, "onResumeFragment()");    Toast.makeText(getActivity(), "onResumeFragment():" + TAG, Toast.LENGTH_SHORT).show(); }

4) Call interface methods on ViewPager page changeYou can set OnPageChangeListener on ViewPager and get callback each time when ViewPager shows another page:

pager.setOnPageChangeListener(pageChangeListener);

5) Implement OnPageChangeListener to call your custom Lifecycle methods

Listener knows the new position and can call the interface method on new Fragment with the help of PagerAdapter. I can here call onResumeFragment() for new fragment and onPauseFragment() on the current one.

I need to store also the current fragment’s position (initially the current position is equal to 0), since I don’t know whether the user scrolled from left to right or from right to left. See what I mean in code:

private OnPageChangeListener pageChangeListener = new OnPageChangeListener() {    int currentPosition = 0;    @Override    public void onPageSelected(int newPosition) {        FragmentLifecycle fragmentToShow = (FragmentLifecycle)pageAdapter.getItem(newPosition);        fragmentToShow.onResumeFragment();        FragmentLifecycle fragmentToHide = (FragmentLifecycle)pageAdapter.getItem(currentPosition);        fragmentToHide.onPauseFragment();        currentPosition = newPosition;    }    @Override    public void onPageScrolled(int arg0, float arg1, int arg2) { }    public void onPageScrollStateChanged(int arg0) { }};

I didn't write the code. Full tutorial here: http://looksok.wordpress.com/2013/11/02/viewpager-with-detailed-fragment-lifecycle-onresumefragment-including-source-code/

Use this

viewPager.setOffscreenPageLimit(1); // the number of pages you want to load in background

and also a ProgressDialogue.

ViewPager creates views for fragments adjacent to your current page. This also gives you an opportunity to load any data required for the adjacent fragments. If you are using AsyncTasks to load data, using this feature will result in a better user experience. But if you need an event when a particular page is opened by the viewpager, LordRaydenMK's solution will work.

See my post on the following thread for using AsyncTasks in a ViewPager:

AsyncTask runs on each page of the ViewPager