使用FragmentPagerAdapter从活动中调用Fragment方法

Question

Originally I had a single fragment loaded in my MainActivity class. I used the following in

onCreate

 if (savedInstanceState == null) {
            getSupportFragmentManager().beginTransaction()
                    .add(new TimeTableFragment(), TIMETABLEFRAGMENT_TAG)
                    .commit();
        }

and in

onResume

if(*setting has changed*){
 TimeTableFragment tf = (TimeTableFragment) getSupportFragmentManager()
                    .findFragmentByTag(TIMETABLEFRAGMENT_TAG);
            if (null != tf) {
                tf.onStudentIdChanged();
            }
}

The onStudentIdChanged() method would refresh the fragment data as preference settings have changed.

I have now refactored this activity to use FragmentPagerAdapter and load two different fragments in tabs. Both fragments are instances of the same TimetableFragment class, but with different parameters passed when creating.

FragmentPagerAdapter methods

@Override
    public Fragment getItem(int position) {
        // getItem is called to instantiate the fragment for the given page.
        // Return a Fragment
        switch (position) {
            case 1:
            case 2:
                return TimeTableFragment.newInstance(position);
            case 0:
                //todo add the single day here
                return TimeTableFragment.newInstance(position);
        }
        return null;
    }

TimetableFragment Method

 public static TimeTableFragment newInstance(int sectionNumber) {
        TimeTableFragment fragment = new TimeTableFragment();
        Bundle args = new Bundle();
        args.putInt(ARG_SECTION_NUMBER, sectionNumber);
        fragment.setArguments(args);
        return fragment;
    }

Now that this is working, in onResume of my MainActivity I am no longer able to access the Fragments using findFragmentByTag , as they are not added in this way during onCreate and I can no longer call the onStudentIdChanged method.

How, for all created instances of the Timetable Fragment can I call this method and have the data updated / refreshed?

Answer 1

In your FragmentPagerAdapter imprementation, add private SparseArray<Fragment> mFragments = new SparseArray<Fragment>();

Modify your getItem method as follows:

@Override
public Fragment getItem(int position) {
    // getItem is called to instantiate the fragment for the given page.
    // Return a Fragment
    Fragment fragment = null;
    switch (position) {
        case 1:
        case 2:
        fragment = mFragments.get(position);
        if (fragment == null) {
            fragment = TimeTableFragment.newInstance(position);
            mFragments.append(position, fragment)
        }
        break;
        case 0:
        //todo add the single day here
        fragment = mFragments.get(position);
        if (fragment == null) {
            fragment = TimeTableFragment.newInstance(position);
            mFragments.append(position, fragment)
        }
        break;
    }

    return fragment;
}

Now when you can get instance of fragment by position.