How to refresh a fragment in a viewpager?

Question

I know there are already some questions to this problem. But I am really new in Android and ecspecially to Fragments and Viewpager. Pls have passion with me. I didn't found a answer which fits to my code.

I dont know how to refresh a fragment or reload it when it's "active" again.

TabsPagerAdapter.java:

public class TabsPagerAdapter extends FragmentPagerAdapter{


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

    @Override
    public Fragment getItem(int index) {

        switch (index) {
        case 0:

            return new KFZFragment();
        case 1:

            return new LogFragment();
        case 2:

            return new TrackFragment();
        }

        return null;
    }

    @Override
    public int getCount() {
        // get item count - equal to number of tabs
        return 3;
    }

}

I have this 3 Fragments (KFZFragment,LogFragment,TrackFragment) and on the TrackFragment I calculate some data and this data should be display in a ListView in LogFragment. But when I change to LogFragment it's not the latest data. So it doesnt refresh.

Now how should I modify my code to refresh the fragments when it's "active"?

MainActivityFragment.java:

public class MainActivityFragment extends FragmentActivity implements ActionBar.TabListener{

    private ViewPager viewPager;
    private TabsPagerAdapter mAdapter;
    private ActionBar actionBar;
    List<Fragment> fragments;

    private String[] tabs = { "KFZ", "Fahrten Log", "Kosten Track" };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main_fragment);

        // Initilization
        viewPager = (ViewPager) findViewById(R.id.pager);
        actionBar = getActionBar();
        mAdapter = new TabsPagerAdapter(getSupportFragmentManager());

       fragments = new Vector<Fragment>();
        fragments.add(Fragment.instantiate(this, KFZFragment.class.getName(),savedInstanceState));
        fragments.add(Fragment.instantiate(this, LogFragment.class.getName(),savedInstanceState));

        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) {
            }
        });
    }   
    @Override
    public void onTabReselected(Tab tab, FragmentTransaction ft) {
        // TODO Auto-generated method stub

    }

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

    }

    @Override
    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        // TODO Auto-generated method stub

    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {


        }
        return super.onKeyDown(keyCode, event);
    }

}

Pls help me out.

Answer 1

I agree with Jonathan Lin

But if the fragment you want to update is the fragment that is currently shown you can do something similar to this:

public class DisplayPagerAdapter extends FragmentPagerAdapter {

private static final String TAG = "DisplayPagerAdapter";

SparseArray<DisplayFragment> registeredFragments = new SparseArray<DisplayFragment>();

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

@Override
public int getCount() {
    DisplayCoreModule display = DisplayCoreModule.getInstance();
    return (display != null && display.getPagesCount() > 0) ? display.getPagesCount() : 1;
}

@Override
public int getItemPosition(Object object) {
    return POSITION_NONE;
}


@Override
public Fragment getItem(int position) {
    Log.d(TAG, "getItem " + position);
    return DisplayFragment.newInstance(position); 
}

@Override
public CharSequence getPageTitle(int position) {
    DisplayCoreModule display = DisplayCoreModule.getInstance();
    if (display != null && display.getPagesCount() > 0) {
        return "Side " + (position+1);
    } else {
        return super.getPageTitle(position);
    }
}

@Override
public Object instantiateItem(ViewGroup container, int position) {
    Log.d(TAG, "instantiateItem " + position);
    DisplayFragment fragment = (DisplayFragment) super.instantiateItem(container, position);
    registeredFragments.put(position, fragment);
    return fragment;
}

@Override
public void destroyItem(ViewGroup container, int position, Object object) {
    Log.d(TAG, "destroyItem " + position);
    registeredFragments.remove(position);
    super.destroyItem(container, position, object);
}

public Fragment getRegisteredFragment(int position) {
    return registeredFragments.get(position);
}

public SparseArray<DisplayFragment> getRegisteredFragments() {
    return registeredFragments;
}

}

It is the registeredFragments part that I wanted to show you.

Since you use FragmentPagerAdapter then getRegisteredFragment(int position) will always return one of your fragments given that you provide a valid position. Should you change to FragmentStatePagerAdapter at some point, it can return null on some of the positions.

Now, in TrackFragment create a callback to your MainActivity, which then informs LogFragment, shown here in pseudo code:

Fragment TrackFragment  {

    interface TrackFragmentCallback() {
        public void newInfo()
    }

    TrackFragmentCallback trackFragmentCallback;

    onAttatch() {
        // make sure to implement TrackFragmentCallback on MainActivity 
        trackFragmentCallback = (TrackFragmentCallback)getActivity();
    } 

    // When this fragment has new info, simply do:
    trackFragmentCallback.newInfo();
}

MainActivity implements TrackFragmentCallback {

    newInfo() {
        // get LogFragment
        LogFragment logFragment = pagerAdapter.getRegisteredFragment(1); 
        if (logFragment != null) {
            logFragment.update();
        }
    }
}

Hope this helps.

Answer 2

Why not? use static methods to refresh the data

Answer 3

In each of your KFZFragment, LogFragment, and TrackFragment, you should be able to override onResume in your fragment class and put your necessary refresh/reload code there.