Hi everybody!
On Wednesday, May 29, 2013 9:35:49 PM UTC+2, Miha wrote:
>
> I'll post the whole mechanics tomorrow.
>
So, to give some context: I'm using a ViewPager with
FragmentStatePageAdapter, where I have three fragments. Two of those
fragments (first and third), also nest another fragments inside. The first
one has a two-pane layout, and the third one is sort of a file-browser
where three types of fragments change (computer, shares, files).
We know that when we derive our activity, the BACK key is handled for us
automatically by the FragmentActivity base class. This is of course not the
case for nested fragments, where I need to "clear the backstack"
appropriately. So for that, I've defined and implemented a simple interface:
public interface BackButtonPressListener {
boolean onBackButtonPressed();
}
I use this interface from the main Activity, which implements this
interface. So when a Back key is pressed, I get the current fragmet from
FragmentStatePageAdapter, and call onBackButtonPressed on that fragment. If
this fragment is able to "pop" the back-stack, I leave it at that. If not,
I let the base activity handle the key press.
I had the problem with FragmentStatePageAdapter, more so with its
getItem(int) method. I was under the impression that this method would get
the current fragment, but it is actually intended to **create** fragments;
FragmentStatePageAdapter internally caches those instances for viewPager,
so I went about implementing my own cache for that as well (since
FragmentStatePageAdapter's cache is private). I overrode the method
instantiateItem with such implementation:
public Object instantiateItem(ViewGroup container, int position) {
Object item = super.instantiateItem(container, position);
_items.put(position, item);
return item;
}
where _items is a private member of type SparseArray<Fragment>.
I added a simple method to get the reference to the current fragment being
shown inside a ViewPager to my page adapter:
public Fragment getCreatedItem(int position)
{
Object item = _items.get(position, null);
if (item != null)
{
return (Fragment) item;
}
Log.v(TAG, _items.toString());
throw new RuntimeException("No matching item in an inner array or item
is null..."); // shouldn't happen
}
The "onBackButtonPressed" in the "main" (top-level) fragments handler
implementation is very simple as well:
@Override
public boolean onBackButtonPressed() {
try {
return FragmentManager fragmentManager =
getChildFragmentManager().popBackStackImmediate();
} catch (Exception x) {
Log.e(TAG, "Could not pop back stack!", x);
}
return false;
}
All of my fragments implement onSaveInstanceState to store state and so
far, everything works as expected (screen orientation changes, resuming an
app, back presses).
I hope this helps someone as well, given some misleading information out
there.
Regards,
Miha.
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