call a method on a fragment in a ViewPager

Question

All I want to do is calling a function of my Fragment's class. But I can't seem to find a way to access the instance of my fragments which are in a ViewPager.

my activity's xml:

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" />

There is no so I can't call findFragmentById() (can I?) also I don't know what to give to findFragmentByTag(), it always return null :/

Answer 1

The pagerAdapter.getItem(int) method usually creates a new instance of the fragment, however, so what you can do is use a HashMap to store a reference to the already existing fragments.

// ViewPagerAdapter
private HashMap<Integer, Fragment> fragmentHashMap = new HashMap<>();

@Override
public Fragment getItem(int position) {
    if (fragmentHashMap.get(position) != null) {
        return fragmentHashMap.get(position);
    }
    TabFragment tabFragment = new TabFragment();
    fragmentHashMap.put(position, tabFragment);
    return tabFragment;
}

Then you can find your fragment to call its methods:

FragmentAdapter fa = (FragmentAdapter)viewPager.getAdapter();
TabFragment theFragment = (TabFragment)fa.getItem(index);
theFragment.customMethod(Object obj);

You will have to keep track of which fragment goes with which index because you cast them to their specific class in order to access their methods.

Answer 2

The ViewPager should have an FragmentAdapter associated with it. So you can do something like:

FragmentAdapter fa = (FragmentAdapter)viewPager.getAdapter();
Fragment f = fa.getItem(index);