DynamicFragmentStatePagerAdapter.java

import android.annotation.SuppressLint;
import android.os.Bundle;
import android.os.Parcelable;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.util.LongSparseArray;
import android.support.v4.view.PagerAdapter;
import android.view.View;
import android.view.ViewGroup;

import java.util.HashSet;
import java.util.Set;

/**
 * An implementation of {@link PagerAdapter} similar to {@link android.support.v4.app.FragmentStatePagerAdapter}
 * which items can be changed dynamically.
 */
public abstract class DynamicFragmentStatePagerAdapter extends PagerAdapter {
    private static final String KEY_FRAGMENTS = "fragments";
    private static final String KEY_STATES = "states";

    private final FragmentManager fragmentManager;
    private final LongSparseArray<Fragment> fragments = new LongSparseArray<>();
    private final LongSparseArray<Fragment.SavedState> savedStates = new LongSparseArray<>();
    private FragmentTransaction currentTransaction;
    private Fragment currentPrimaryItem;

    public DynamicFragmentStatePagerAdapter(FragmentManager fragmentManager) {
        this.fragmentManager = fragmentManager;
    }

    public abstract Fragment getItem(int position);

    public abstract long getItemId(int position);

    @Nullable
    public Fragment getItemById(long itemId) {
        return fragments.get(itemId);
    }

    @Override
    @SuppressLint("CommitTransaction")
    public Object instantiateItem(ViewGroup container, int position) {
        final long itemId = getItemId(position);
        Fragment fragment = fragments.get(itemId);
        if (fragment != null) {
            return fragment;
        }
        fragment = getItem(position);
        final Fragment.SavedState savedState = savedStates.get(itemId);
        if (savedState != null) {
            fragment.setInitialSavedState(savedState);
        }
        fragment.setMenuVisibility(false);
        fragment.setUserVisibleHint(false);
        fragments.put(itemId, fragment);

        if (currentTransaction == null) {
            currentTransaction = fragmentManager.beginTransaction();
        }
        currentTransaction.add(container.getId(), fragment);
        return fragment;
    }

    @Override
    @SuppressLint("CommitTransaction")
    public void destroyItem(ViewGroup container, int position, Object object) {
        final Fragment fragment = (Fragment) object;

        final int index = fragments.indexOfValue(fragment);
        final long itemId = fragments.keyAt(index);

        if (fragment.isAdded() && getItemPosition(fragment) != POSITION_NONE) {
            savedStates.put(itemId, fragmentManager.saveFragmentInstanceState(fragment));
        } else {
            savedStates.remove(itemId);
        }

        fragments.removeAt(index);

        if (currentTransaction == null) {
            currentTransaction = fragmentManager.beginTransaction();
        }
        currentTransaction.remove(fragment);
    }

    @Override
    public void setPrimaryItem(ViewGroup container, int position, Object object) {
        final Fragment fragment = (Fragment) object;
        if (currentPrimaryItem != fragment) {
            if (currentPrimaryItem != null) {
                currentPrimaryItem.setMenuVisibility(false);
                currentPrimaryItem.setUserVisibleHint(false);
            }
            if (fragment != null) {
                fragment.setMenuVisibility(true);
                fragment.setUserVisibleHint(true);
            }
            currentPrimaryItem = fragment;
        }
    }

    @Override
    public void startUpdate(ViewGroup container) {
        if (container.getId() == View.NO_ID) {
            throw new IllegalStateException("ViewPager with adapter " + this + " requires a view id");
        }
    }

    @Override
    public void finishUpdate(ViewGroup container) {
        if (currentTransaction != null) {
            currentTransaction.commitNowAllowingStateLoss();
            currentTransaction = null;
        }
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return ((Fragment) object).getView() == view;
    }

    @Override
    public int getItemPosition(Object object) {
        final Fragment fragment = (Fragment) object;
        final int index = fragments.indexOfValue(fragment);
        if (index != -1) {
            final long itemId = fragments.keyAt(index);
            for (int position = 0, itemCount = getCount(); position < itemCount; position++) {
                final long currentItemId = getItemId(position);
                if (currentItemId == itemId) {
                    return position;
                }
            }
        }
        return POSITION_NONE;
    }

    @Override
    public void notifyDataSetChanged() {
        super.notifyDataSetChanged();
        purgeStates();
    }

    @Override
    public Parcelable saveState() {
        final Bundle state = new Bundle();
        final int stateCount = savedStates.size();
        if (stateCount > 0) {
            final Bundle stateBundle = new Bundle();
            for (int i = 0; i < stateCount; i++) {
                stateBundle.putParcelable(String.valueOf(savedStates.keyAt(i)), savedStates.valueAt(i));
            }
            state.putBundle(KEY_STATES, stateBundle);
        }
        final int fragmentCount = fragments.size();
        if (fragmentCount > 0) {
            final Bundle fragmentBundle = new Bundle();
            for (int i = 0; i < fragmentCount; i++) {
                final Fragment fragment = fragments.valueAt(i);
                if (fragment.isAdded()) {
                    fragmentManager.putFragment(fragmentBundle, String.valueOf(fragments.keyAt(i)), fragment);
                }
            }
            state.putBundle(KEY_FRAGMENTS, fragmentBundle);
        }
        return state;
    }

    @Override
    public void restoreState(Parcelable state, ClassLoader loader) {
        final Bundle bundle = (Bundle) state;
        bundle.setClassLoader(loader);

        fragments.clear();
        savedStates.clear();

        final Bundle stateBundle = bundle.getBundle(KEY_STATES);
        if (stateBundle != null) {
            for (String key : stateBundle.keySet()) {
                savedStates.put(Long.parseLong(key), stateBundle.getParcelable(key));
            }
        }
        final Bundle fragmentsBundle = bundle.getBundle(KEY_FRAGMENTS);
        if (fragmentsBundle != null) {
            for (String key : fragmentsBundle.keySet()) {
                final Fragment fragment = fragmentManager.getFragment(fragmentsBundle, key);
                if (fragment != null) {
                    fragment.setMenuVisibility(false);
                    fragments.put(Long.parseLong(key), fragment);
                }
            }
        }
    }

    private void purgeStates() {
        final Set<Long> itemIds = new HashSet<>();
        for (int position = 0, itemCount = getCount(); position < itemCount; position++) {
            final long itemId = getItemId(position);
            itemIds.add(itemId);
        }

        for (int index = 0; index < savedStates.size(); ) {
            final long itemId = savedStates.keyAt(index);
            if (!itemIds.contains(itemId)) {
                savedStates.removeAt(index);
            } else {
                index++;
            }
        }
    }
}