Class members in Fragment become null after Home button press and wait

Question

Problem Description Application which I'm writing has 3 Fragments. Main Fragment Activity has a Search Box with Search button when I press on a Search button the function below is called: ``` Fragments.values()[tabControl.getCurrentItem()].getFragment().search(tv.getText().toString(), MainActivity.this.getApplicationContext()); ``` Everything works Okay until I press HOME button wait for 30 minutes and relaunch application, after I press Search button in `FragmentYellowPages` Fragment application crashes on the lines ``` lvYellowPages.setVisibility(View.VISIBLE); ``` as `lvYellowPages` in this case is null, but In a logs I can see that `onCreateView` function is called. Can you please help me, I can share my code with you. FragmentPagerAdapter ``` public class FragmentAdapter extends FragmentPagerAdapter { Fragments[] mFragments; public FragmentAdapter(FragmentManager fm) { super(fm); mFragments = Fragments.values(); } public enum Fragments { Favorites(App.getStringByResId(R.string.fa…

Accepted Answer

It's hard to pinpoint the exact problem but I'm almost sure it has to do with the way you built the adapter for the `ViewPager`.

Everything works Okay until I press HOME button wait for 30 minutes and relaunch application, after I press Search button in FragmentYellowPages Fragment application crashes

As the `Activity` is in the background(and apparently killed) it will recreate its content when comming back to the foreground. At this point the `ViewPager` will rebuild its content, but its adapter will not call `getItem()` as it has all the data to recreate the previous fragments on it own. So you'll end up with two fragment version, the ones currently visible in the `ViewPager`(so you see the `onCreateView()` being called) and those that are in the `enum`. Those fragments from the `enum` aren't tied to the `Activity` and so the entire callbacks stack isn't run for them, so `onCreateView()` will not be called, which will make your lvYellowPages `ListView` `null`.

Btw, this is the first time I've seen the fragments of an adapter being built in a `enum` and I recommend that you avoid this.

The solution is to not reference the fragments of the `ViewPager` outside. Make the `getItem()` method return a `Fragment` instance and if you need to access those fragment there are ways to do it without storing the `ViewPager`'s fragment in lists/enums etc(a quick search on stackoverflow should show you a question about this):

```
@Override
public Fragment getItem(int position) {
    switch (position) {
    case 0:
       return new FragmentFavorites();
    case 1:
       return new FragmentCategories();
    case 2:
       return new FragmentYellowPages();
    }
    return null;
}

@Override
public int getCount() {
    return 3;
}
```

Also:

```
setRetainInstance(true);
```

I wouldn't use this. It doesn't make sense to retain a fragment used by a `ViewPager`(as I don't think you're planing to move it somewhere else) and it will also not protect you from the activity being killed in the background.

Class members in Fragment become null after Home button press and wait

Solution

Problem

Related problems