Java tutorial
/* * Copyright (C) 2011 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.kevinread.sortablefragmentpager; import android.os.Bundle; 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.view.PagerAdapter; import android.util.Log; import android.view.View; import android.view.ViewGroup; import java.util.ArrayList; import java.util.Arrays; /** * Implementation of {@link android.support.v4.view.PagerAdapter} that * uses a {@link android.support.v4.app.Fragment} to manage each page. This class also handles * saving and restoring of fragment's state. * * <p>This version of the pager is more useful when there are a large number * of pages, working more like a list view. When pages are not visible to * the user, their entire fragment may be destroyed, only keeping the saved * state of that fragment. This allows the pager to hold on to much less * memory associated with each visited page as compared to * {@link android.support.v4.app.FragmentPagerAdapter} at the cost of potentially more overhead when * switching between pages. * * <p>When using FragmentPagerAdapter the host ViewPager must have a * valid ID set.</p> * * <p>Subclasses only need to implement {@link #getItem(int)} * and {@link #getCount()} to have a working adapter. * * <p>Here is an example implementation of a pager containing fragments of * lists: * * {@sample development/samples/Support13Demos/src/com/example/android/supportv13/app/FragmentStatePagerSupport.java * complete} * * <p>The <code>R.layout.fragment_pager</code> resource of the top-level fragment is: * * {@sample development/samples/Support13Demos/res/layout/fragment_pager.xml * complete} * * <p>The <code>R.layout.fragment_pager_list</code> resource containing each * individual fragment's layout is: * * {@sample development/samples/Support13Demos/res/layout/fragment_pager_list.xml * complete} */ public abstract class SortableFragmentStatePagerAdapter extends PagerAdapter { private static final String TAG = "SortableFragmentStatePagerAdapter"; private static final boolean DEBUG = false; private final FragmentManager mFragmentManager; private FragmentTransaction mCurTransaction = null; private long[] mItemIds = new long[] {}; private ArrayList<Fragment.SavedState> mSavedState = new ArrayList<Fragment.SavedState>(); private ArrayList<Fragment> mFragments = new ArrayList<Fragment>(); private Fragment mCurrentPrimaryItem = null; public SortableFragmentStatePagerAdapter(FragmentManager fm) { mFragmentManager = fm; createIdCache(); } /** * Return the Fragment associated with a specified position. */ public abstract Fragment getItem(int position); /** * Return a unique identifier for the item at the given position. */ public abstract long getItemId(int position); @Override public void startUpdate(ViewGroup container) { } private void checkForIdChanges() { long[] newItemIds = new long[getCount()]; for (int i = 0; i < newItemIds.length; i++) { newItemIds[i] = getItemId(i); } if (!Arrays.equals(mItemIds, newItemIds)) { ArrayList<Fragment.SavedState> newSavedState = new ArrayList<Fragment.SavedState>(); ArrayList<Fragment> newFragments = new ArrayList<Fragment>(); for (int oldPosition = 0; oldPosition < mItemIds.length; oldPosition++) { int newPosition = POSITION_NONE; for (int i = 0; i < newItemIds.length; i++) { if (mItemIds[oldPosition] == newItemIds[i]) { newPosition = i; break; } } if (newPosition >= 0) { if (oldPosition < mSavedState.size()) { Fragment.SavedState savedState = mSavedState.get(oldPosition); if (savedState != null) { while (newSavedState.size() <= newPosition) { newSavedState.add(null); } newSavedState.set(newPosition, savedState); } } if (oldPosition < mFragments.size()) { Fragment fragment = mFragments.get(oldPosition); if (fragment != null) { while (newFragments.size() <= newPosition) { newFragments.add(null); } newFragments.set(newPosition, fragment); } } } } mItemIds = newItemIds; mSavedState = newSavedState; mFragments = newFragments; } } @Override public void notifyDataSetChanged() { checkForIdChanges(); super.notifyDataSetChanged(); } /** * Create the initial set of item IDs. Run this after you have set your adapter data. */ public void createIdCache() { // If we have already stored ids, don't overwrite them if (mItemIds.length == 0) { // getCount might have overhead, so run it as late as possible final int count = getCount(); if (count > 0) { mItemIds = new long[count]; for (int i = 0; i < count; i++) { mItemIds[i] = getItemId(i); } } } } @Override public Object instantiateItem(ViewGroup container, int position) { createIdCache(); // If we already have this item instantiated, there is nothing // to do. This can happen when we are restoring the entire pager // from its saved state, where the fragment manager has already // taken care of restoring the fragments we previously had instantiated. if (mFragments.size() > position) { Fragment f = mFragments.get(position); if (f != null) { return f; } } if (mCurTransaction == null) { mCurTransaction = mFragmentManager.beginTransaction(); } Fragment fragment = getItem(position); if (DEBUG) Log.v(TAG, "Adding item #" + position + ": f=" + fragment); if (mSavedState.size() > position) { Fragment.SavedState fss = mSavedState.get(position); if (fss != null) { fragment.setInitialSavedState(fss); } } while (mFragments.size() <= position) { mFragments.add(null); } fragment.setMenuVisibility(false); fragment.setUserVisibleHint(false); mFragments.set(position, fragment); mCurTransaction.add(container.getId(), fragment); return fragment; } @Override public void destroyItem(ViewGroup container, int position, Object object) { Fragment fragment = (Fragment) object; if (mCurTransaction == null) { mCurTransaction = mFragmentManager.beginTransaction(); } if (DEBUG) Log.v(TAG, "Removing item #" + position + ": f=" + object + " v=" + ((Fragment) object).getView()); while (mSavedState.size() <= position) { mSavedState.add(null); } mSavedState.set(position, mFragmentManager.saveFragmentInstanceState(fragment)); if (mFragments.size() > position) mFragments.set(position, null); mCurTransaction.remove(fragment); } @Override public void setPrimaryItem(ViewGroup container, int position, Object object) { Fragment fragment = (Fragment) object; if (fragment != mCurrentPrimaryItem) { if (mCurrentPrimaryItem != null) { mCurrentPrimaryItem.setMenuVisibility(false); mCurrentPrimaryItem.setUserVisibleHint(false); } if (fragment != null) { fragment.setMenuVisibility(true); fragment.setUserVisibleHint(true); } mCurrentPrimaryItem = fragment; } } @Override public void finishUpdate(ViewGroup container) { if (mCurTransaction != null) { mCurTransaction.commitAllowingStateLoss(); mCurTransaction = null; mFragmentManager.executePendingTransactions(); } } @Override public boolean isViewFromObject(View view, Object object) { return ((Fragment) object).getView() == view; } @Override public Parcelable saveState() { Bundle state = null; mItemIds = new long[getCount()]; for (int i = 0; i < mItemIds.length; i++) { mItemIds[i] = getItemId(i); } if (mSavedState.size() > 0) { state = new Bundle(); if (mItemIds.length > 0) { state.putLongArray("itemids", mItemIds); } Fragment.SavedState[] fss = new Fragment.SavedState[mSavedState.size()]; mSavedState.toArray(fss); state.putParcelableArray("states", fss); } for (int i = 0; i < mFragments.size(); i++) { Fragment f = mFragments.get(i); if (f != null) { if (state == null) { state = new Bundle(); } String key = "f" + i; mFragmentManager.putFragment(state, key, f); } } return state; } @Override public void restoreState(Parcelable state, ClassLoader loader) { if (state != null) { Bundle bundle = (Bundle) state; bundle.setClassLoader(loader); mItemIds = bundle.getLongArray("itemids"); if (mItemIds == null) { mItemIds = new long[] {}; } Parcelable[] fss = bundle.getParcelableArray("states"); mSavedState.clear(); mFragments.clear(); if (fss != null) { for (int i = 0; i < fss.length; i++) { mSavedState.add((Fragment.SavedState) fss[i]); } } Iterable<String> keys = bundle.keySet(); for (String key : keys) { if (key.startsWith("f")) { int index = Integer.parseInt(key.substring(1)); Fragment f = mFragmentManager.getFragment(bundle, key); if (f != null) { while (mFragments.size() <= index) { mFragments.add(null); } f.setMenuVisibility(false); mFragments.set(index, f); } else { Log.w(TAG, "Bad fragment at key " + key); } } } checkForIdChanges(); } } }