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/* | |
Extension of FragmentStatePagerAdapter which intelligently caches | |
all active fragments and manages the fragment lifecycles. | |
Usage involves extending from SmartFragmentStatePagerAdapter as you would any other PagerAdapter. | |
*/ | |
public abstract class SmartFragmentStatePagerAdapter extends FragmentStatePagerAdapter { | |
// Sparse array to keep track of registered fragments in memory | |
private SparseArray<Fragment> registeredFragments = new SparseArray<Fragment>(); | |
public SmartFragmentStatePagerAdapter(FragmentManager fragmentManager) { | |
super(fragmentManager); | |
} | |
// Register the fragment when the item is instantiated | |
@Override | |
public Object instantiateItem(ViewGroup container, int position) { | |
Fragment fragment = (Fragment) super.instantiateItem(container, position); | |
registeredFragments.put(position, fragment); | |
return fragment; | |
} | |
// Unregister when the item is inactive | |
@Override | |
public void destroyItem(ViewGroup container, int position, Object object) { | |
registeredFragments.remove(position); | |
super.destroyItem(container, position, object); | |
} | |
// Returns the fragment for the position (if instantiated) | |
public Fragment getRegisteredFragment(int position) { | |
return registeredFragments.get(position); | |
} | |
} |
For those running into orientation change issues on rotation, I wanted to post a quick fix until we have a better workaround. In the SmartFragmentStatePagerAdapter
class, extend with:
// Add to `SmartFragmentStatePagerAdapter.java` as a new method
// Returns the fragment for the position (if instantiated)
public Fragment fetchFragmentByPosition(ViewGroup pagerInstance, int position) {
Fragment existingInstance = registeredFragments.get(position);
if (existingInstance != null) {
return existingInstance;
} else {
return instantiateItem(pagerInstance, position);
}
}
In the parent activity or fragment where the adapter instance is available:
// In the Activity or wherever you have access to the view pager instance
adapter.fetchFragmentByPosition(mPager, 0);
This should allow you to get access to the instance even when the registeredFragments
becomes null on orientation change. Can anyone else report back on if this code a) is working on orientation change b) isn't working on orientation change or c) proposed workaround
@nesquena
Above code works great, just checked. One small correction to the above code, a type cast is required for the return statement -
return (Fragment)instantiateItem(pagerInstance, position);
To simplify the class, I think we can have only one method instead of two doing the same work of getting the Registered Fragment -
// Returns the fragment for the position (if instantiated)
public Fragment getRegisteredFragment(int position) {
Fragment existingInstance = registeredFragments.get(position);
if (existingInstance != null) {
return existingInstance;
} else {
return (Fragment) instantiateItem(pagerInstance, position);
}
}
Wish I had this code earlier. I came across such a situation, and did not know what to do. Spent a lot of time, and finally made a hack from reading the internal code of FragmentStatePagerAdapter
. Below is what I came up with, but your solution is very simple.
//Sparse Array to keep track of the registered fragments in memory
private SparseArray<Fragment> mRegisteredFragments = new SparseArray<>();
//Stores a reference to the FragmentManager used
private FragmentManager mFragmentManager;
public SmartFragmentStatePagerAdapter(FragmentManager fragmentManager) {
super(fragmentManager);
mFragmentManager = fragmentManager;
}
/**
* Overriding to restore the state of Registered Fragments array
*
* @param state is the Parcelable state
* @param loader is the ClassLoader required for restoring the state
*/
@Override
public void restoreState(Parcelable state, ClassLoader loader) {
super.restoreState(state, loader);
if (state != null) {
//When the state is present
Bundle bundle = (Bundle) state;
//Setting the ClassLoader passed, onto the Bundle
bundle.setClassLoader(loader);
//Retrieving the keys used in Bundle
Set<String> keyStringSet = bundle.keySet();
//Iterating over the Keys to find the Fragments
for (String keyString : keyStringSet) {
if (keyString.startsWith("f")) {
//Fragment keys starts with 'f' followed by its position index
int position = Integer.parseInt(keyString.substring(1));
//Getting the Fragment from the Bundle using the Key through the FragmentManager
Fragment fragment = mFragmentManager.getFragment(bundle, keyString);
if (fragment != null) {
//If Fragment is valid, then update the Sparse Array of Registered Fragments
mRegisteredFragments.put(position, fragment);
}
}
}
}
}
I'm getting FragmentStatePagerAdapter cannot be applied to (android.app.FragmentManager)
on the line:
public SmartFragmentStatePagerAdapter(FragmentManager fragmentManager) {
super(fragmentManager);
}
Do you know what might be causing this?
EDIT:
I had to change:
import android.app.Fragment;
import android.app.FragmentManager;
to:
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
I'm still having trouble getting this to work after rotation. Is there an example project?
firstly thanks you! hoping it is useful to me,