/* * Copyright (C) 2011 Google Inc. * Licensed to The Android Open Source Project. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.android.ex.photo.adapters; import android.os.Parcelable; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v4.app.FragmentTransaction; import android.support.v4.util.LruCache; import android.support.v4.view.PagerAdapter; import android.util.Log; import android.view.View; /** * NOTE: This is a direct copy of {@link android.support.v4.app.FragmentPagerAdapter} * with four very important modifications. *

*

    *
  1. The method {@link #makeFragmentName(int, int)} is declared "protected" * in our class. We need to be able to re-define the fragment's name according to data * only available to sub-classes.
  2. *
  3. The method {@link #isViewFromObject(View, Object)} has been reimplemented to search * the entire view hierarchy for the given view.
  4. *
  5. In method {@link #destroyItem(View, int, Object)}, the fragment is detached and * added to a cache. If the fragment is evicted from the cache, it will be deleted. * An album may contain thousands of photos and we want to avoid having thousands of * fragments.
  6. *
*/ public abstract class BaseFragmentPagerAdapter extends PagerAdapter { /** The default size of {@link #mFragmentCache} */ private static final int DEFAULT_CACHE_SIZE = 5; private static final String TAG = "FragmentPagerAdapter"; private static final boolean DEBUG = false; private final FragmentManager mFragmentManager; private FragmentTransaction mCurTransaction = null; private Fragment mCurrentPrimaryItem = null; /** A cache to store detached fragments before they are removed */ private LruCache mFragmentCache = new FragmentCache(DEFAULT_CACHE_SIZE); public BaseFragmentPagerAdapter(android.support.v4.app.FragmentManager fm) { mFragmentManager = fm; } /** * Return the Fragment associated with a specified position. */ public abstract Fragment getItem(int position); @Override public void startUpdate(View container) { } @Override public Object instantiateItem(View container, int position) { if (mCurTransaction == null) { mCurTransaction = mFragmentManager.beginTransaction(); } // Do we already have this fragment? String name = makeFragmentName(container.getId(), position); // Remove item from the cache mFragmentCache.remove(name); Fragment fragment = mFragmentManager.findFragmentByTag(name); if (fragment != null) { if (DEBUG) Log.v(TAG, "Attaching item #" + position + ": f=" + fragment); mCurTransaction.attach(fragment); } else { fragment = getItem(position); if(fragment == null) { if (DEBUG) Log.e(TAG, "NPE workaround for getItem(). See b/7103023"); return null; } if (DEBUG) Log.v(TAG, "Adding item #" + position + ": f=" + fragment); mCurTransaction.add(container.getId(), fragment, makeFragmentName(container.getId(), position)); } if (fragment != mCurrentPrimaryItem) { fragment.setMenuVisibility(false); } return fragment; } @Override public void destroyItem(View container, int position, Object object) { if (mCurTransaction == null) { mCurTransaction = mFragmentManager.beginTransaction(); } if (DEBUG) Log.v(TAG, "Detaching item #" + position + ": f=" + object + " v=" + ((Fragment)object).getView()); Fragment fragment = (Fragment) object; String name = fragment.getTag(); if (name == null) { // We prefer to get the name directly from the fragment, but, if the fragment is // detached before the add transaction is committed, this could be 'null'. In // that case, generate a name so we can still cache the fragment. name = makeFragmentName(container.getId(), position); } mFragmentCache.put(name, fragment); mCurTransaction.detach(fragment); } @Override public void setPrimaryItem(View container, int position, Object object) { Fragment fragment = (Fragment) object; if (fragment != mCurrentPrimaryItem) { if (mCurrentPrimaryItem != null) { mCurrentPrimaryItem.setMenuVisibility(false); } if (fragment != null) { fragment.setMenuVisibility(true); } mCurrentPrimaryItem = fragment; } } @Override public void finishUpdate(View container) { if (mCurTransaction != null && !mFragmentManager.isDestroyed()) { mCurTransaction.commitAllowingStateLoss(); mCurTransaction = null; mFragmentManager.executePendingTransactions(); } } @Override public boolean isViewFromObject(View view, Object object) { // Ascend the tree to determine if the view is a child of the fragment View root = ((Fragment) object).getView(); for (Object v = view; v instanceof View; v = ((View) v).getParent()) { if (v == root) { return true; } } return false; } @Override public Parcelable saveState() { return null; } @Override public void restoreState(Parcelable state, ClassLoader loader) { } /** Creates a name for the fragment */ protected String makeFragmentName(int viewId, int index) { return "android:switcher:" + viewId + ":" + index; } /** * A cache of detached fragments. */ private class FragmentCache extends LruCache { public FragmentCache(int size) { super(size); } @Override protected void entryRemoved(boolean evicted, String key, Fragment oldValue, Fragment newValue) { // remove the fragment if it's evicted OR it's replaced by a new fragment if (evicted || (newValue != null && oldValue != newValue)) { mCurTransaction.remove(oldValue); } } } }