Java – refresh the Android viewpager fragment on refresh

I'm new to Android. I really don't understand why the dynamically added fragment content (such as some images added after the button is clicked) disappears after scrolling some fragments and then returning

There are very simple code activities and fragments:

public class MyActivity extends FragmentActivity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        final ViewPager viewPager = (ViewPager) findViewById(R.id.viewPager);
        final CustomAdapter adapter = new CustomAdapter(getSupportFragmentManager());
        viewPager.setAdapter(adapter);
    }

    class CustomFragment extends Fragment {

        @Override
        public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) {
            return inflater.inflate(R.layout.fragment,container,false);
        }

        @Override
        public void onActivityCreated(Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);
            getView().findViewById(R.id.clickMeButton).setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    getView().findViewById(R.id.image).setVisibility(View.VISIBLE);
                }
            });
        }

    }

    class CustomAdapter extends FragmentStatePagerAdapter {

        private List<CustomFragment> fragments = Arrays.asList(
            new CustomFragment(),new CustomFragment(),new CustomFragment()
        );

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

        @Override
        public Fragment getItem(int i) {
            return fragments.get(i);
        }

        @Override
        public int getCount() {
            return fragments.size();
        }
    }

}

And appropriate xmls:

main. In XML

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          android:orientation="vertical"
          android:layout_width="fill_parent"
          android:layout_height="fill_parent">

    <android.support.v4.view.ViewPager
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:id="@+id/viewPager" />

</LinearLayout>

fragment. XML

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          android:orientation="vertical"
          android:layout_width="match_parent"
          android:layout_height="match_parent">

    <Button
            android:id="@+id/clickMeButton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="click me"/>

    <ImageView
            android:id="@+id/image"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@drawable/ic_launcher"
            android:visibility="gone"/>

</LinearLayout>

The logic is simple On each clip, I can click a button and an image will appear

It works But

When I display the image on the first clip, scroll to the third clip and return to the first clip again, and the image disappears

What can I do to prevent this from happening? Should I preserve visibility in some way?

Solution

This happens because the fragmentstatepageradapter frees the memory associated with the fragment when the fragment scrolls out of the view From docs:

You can try one of four options:

1. Because the number of pages is small, you can use fragmentpageradapter instead of fragmentstatepageradapter The fragmentpageradapter retains the created fragments and does not destroy them when sliding

2. In fragment, store a Boolean value in sharedpreference, and set (or clear) its value when making the image visible or invisible Then, in the onresume () method of fragment, make the image visible or invisible according to the value of sharedpreference

3. in Fragment's onCreate (), call setRetainInstance (true);.

4. If the number of fragments is fixed and relatively small, then add the following code to your oncreate():

mViewPager = (ViewPager)findViewById(R.id.pager);
mViewPager.setOffscreenPageLimit(limit);         /* limit is a fixed integer*/