How to determine when Fragment becomes visible in

Question

Problem: Fragment onResume() in ViewPager is fired before the fragment becomes actually visible.

For example, I have 2 fragments with ViewPager and FragmentPagerAdapter. The second fragment is only available for authorized users and I need to ask the user to log in when the fragment becomes visible (using an alert dialog).

BUT the ViewPager creates the second fragment when the first is visible in order to cache the second fragment and makes it visible when the user starts swiping.

So the onResume() event is fired in the second fragment long before it becomes visible. That's why I'm trying to find an event which fires when the second fragment becomes visible to show a dialog at the appropriate moment.

How can this be done?

Answer 1

We have a special case with MVP where the fragment needs to notify the presenter that the view has become visible, and the presenter is injected by Dagger in fragment.onAttach().

setUserVisibleHint() is not enough, we've detected 3 different cases that needed to be addressed (onAttach() is mentioned so that you know when the presenter is available):

1. Fragment has just been created. The system makes the following calls:

   setUserVisibleHint() // before fragment's lifecycle calls, so presenter is null
   onAttach()
   ...
   onResume()
   

2. Fragment already created and home button is pressed. When restoring the app to foreground, this is called:

   onResume()
   

3. Orientation change:

   onAttach() // presenter available
   onResume()
   setUserVisibleHint()
   

We only want the visibility hint to get to the presenter once, so this is how we do it:

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View root = inflater.inflate(R.layout.fragment_list, container, false);
    setHasOptionsMenu(true);

    if (savedInstanceState != null) {
        lastOrientation = savedInstanceState.getInt(STATE_LAST_ORIENTATION,
              getResources().getConfiguration().orientation);
    } else {
        lastOrientation = getResources().getConfiguration().orientation;
    }

    return root;
}

@Override
public void onResume() {
    super.onResume();
    presenter.onResume();

    int orientation = getResources().getConfiguration().orientation;
    if (orientation == lastOrientation) {
        if (getUserVisibleHint()) {
            presenter.onViewBecomesVisible();
        }
    }
    lastOrientation = orientation;
}

@Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    if (presenter != null && isResumed() && isVisibleToUser) {
        presenter.onViewBecomesVisible();
    }
}

@Override public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putInt(STATE_LAST_ORIENTATION, lastOrientation);
}

Answer 2

Detecting by focused view!

This works for me

public static boolean isFragmentVisible(Fragment fragment) {
    Activity activity = fragment.getActivity();
    View focusedView = fragment.getView().findFocus();
    return activity != null
            && focusedView != null
            && focusedView == activity.getWindow().getDecorView().findFocus();
}

Answer 3

I encountered this problem when I was trying to get a timer to fire when the fragment in the viewpager was on-screen for the user to see.

The timer always started just before the fragment was seen by the user. This is because the onResume() method in the fragment is called before we can see the fragment.

My solution was to do a check in the onResume() method. I wanted to call a certain method 'foo()' when fragment 8 was the view pagers current fragment.

@Override
public void onResume() {
    super.onResume();
    if(viewPager.getCurrentItem() == 8){
        foo();
        //Your code here. Executed when fragment is seen by user.
    }
}

Hope this helps. I've seen this problem pop up a lot. This seems to be the simplest solution I've seen. A lot of others are not compatible with lower APIs etc.

Answer 4

UPDATE: Android Support Library (rev 11) finally fixed the user visible hint issue, now if you use support library for fragments, then you can safely use getUserVisibleHint() or override setUserVisibleHint() to capture the changes as described by gorn's answer.

UPDATE 1 Here is one small problem with getUserVisibleHint(). This value is by default true.

// Hint provided by the app that this fragment is currently visible to the user.
boolean mUserVisibleHint = true;

So there might be a problem when you try to use it before setUserVisibleHint() was invoked. As a workaround you might set value in onCreate method like this.

public void onCreate(@Nullable Bundle savedInstanceState) {
    setUserVisibleHint(false);

---

The outdated answer:

In most use cases, ViewPager only show one page at a time, but the pre-cached fragments are also put to "visible" state (actually invisible) if you are using FragmentStatePagerAdapter in Android Support Library pre-r11.

I override :

public class MyFragment extends Fragment {
    @Override
    public void setMenuVisibility(final boolean visible) {
        super.setMenuVisibility(visible);
        if (visible) {
            // ...
        }
    }
   // ...
}

To capture the focus state of fragment, which I think is the most suitable state of the "visibility" you mean, since only one fragment in ViewPager can actually place its menu items together with parent activity's items.

Answer 5

Try this, it's work for me:

@Override
public void onHiddenChanged(boolean hidden) {
        super.onHiddenChanged(hidden);

        if (hidden) {

        }else
        {}
    }

Answer 6

I had the same issue. ViewPager executes other fragment life cycle events and I could not change that behavior. I wrote a simple pager using fragments and available animations. SimplePager