CODEWITHSUNDEEP
androidandroid-fragmentsandroid-viewpager
sergi
sergi

Reputation: 1089

Fragment re-created when change tab with ViewPager

I've got a ViewPager with 4 tabs.

I'm using a custom adapter that extends FragmentPagerAdapter.

The problem is that when I change the tab, the first Fragment gets created again although it's not the currently visible. Moreover, this only happens after changing the tab for the fourth time. E.g. tab1 -> tab2 -> tab3=> onStop from tab1 is called. -> tab2 => onCreateView from tab1 is called (onAttach is not called).

I want to avoid this. I need all tabs to remain always in their state even when they are not currently displayed. How can I do this?

Upvotes: 6

Views: 6984

Answers (3)

live-love
live-love

Reputation: 52366

Viewpager has one public method named setOffScreenPageLimit which indicates the number of pages that will be retained to either side of the current page in the view hierarchy in an idle state.

Activity:

    private SectionsPagerAdapter mSectionsPagerAdapter;
    private ViewPager mViewPager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

...

        mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());

        mViewPager = findViewById(R.id.container);
        mViewPager.setOffscreenPageLimit(3);  // change your number here
        mViewPager.setAdapter(mSectionsPagerAdapter);

Upvotes: 1

sergi
sergi

Reputation: 1089

It's been as easy as using method setOffscreenPageLimit() from ViewPager.

More info: http://developer.android.com/reference/android/support/v4/view/ViewPager.html#setOffscreenPageLimit(int)

Upvotes: 24

Sapan Diwakar
Sapan Diwakar

Reputation: 10946

When you instantiate the fragment, call setRetainInstance(true). This will retain the instance state of the fragment. onCreateView will still be called and you will need to make sure that you re use the saved state and just render the views without loading any data again, e.g. by using a boolean to represent if your fragment has already been initialized.

You would do something like this: 

public static class MyAdapter extends FragmentPagerAdapter {
       @Override
       public Fragment getItem(int position) {
               MyFragment myFragment = new MyFragment();
               myFragment.setRetainInstance(true);
               return myFragment;
       }
}

class MyFragment extends Fragment {
       .
       .
       .

       boolean initialized = false;
       ArrayList<MyData> myData = null;

       void onCreate(...) {
               if (initialized) {
                       renderViews();
               } else {
                       initialized = true;
                       loadData();
                       renderViews();
               }
       }
}

You don't need to implement onSaveInstanceState(). It will be handled automatically.

Upvotes: 0

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