Java tutorial
/* * Copyright (C) 2012 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.mail.utils; import android.app.Fragment; import android.app.FragmentManager; import android.app.FragmentTransaction; import android.os.Bundle; import android.os.Parcelable; import android.support.v13.app.FragmentCompat; import android.support.v13.app.FragmentStatePagerAdapter; import android.support.v4.util.SparseArrayCompat; import android.support.v4.view.PagerAdapter; import android.view.View; import android.view.ViewGroup; import java.util.ArrayList; /** * Forked from support lib's {@link FragmentStatePagerAdapter}, with some minor * changes that couldn't be accomplished through subclassing: * <ul> * <li>optionally disable stateful behavior when paging (controlled by {@link #mEnableSavedStates}), * for situations where state save/restore when paging is unnecessary</li> * <li>override-able {@link #setItemVisible(Fragment, boolean)} method for subclasses to * add supplemental handling of visibility hints manually on pre-v15 devices</li> * <li>add support to handle data set changes that cause item positions to change</li> * <li>allow read access to existing Fragments by index ({@link #getFragmentAt(int)})</li> * </ul> */ public abstract class FragmentStatePagerAdapter2 extends PagerAdapter { private static final String TAG = "FSPA"; // the support lib's tag is too long and crashes :) private static final boolean DEBUG = false; private final FragmentManager mFragmentManager; private FragmentTransaction mCurTransaction = null; private ArrayList<Fragment.SavedState> mSavedState = new ArrayList<Fragment.SavedState>(); private SparseArrayCompat<Fragment> mFragments = new SparseArrayCompat<Fragment>(); private Fragment mCurrentPrimaryItem = null; private boolean mEnableSavedStates; public FragmentStatePagerAdapter2(FragmentManager fm) { this(fm, true); } public FragmentStatePagerAdapter2(FragmentManager fm, boolean enableSavedStates) { mFragmentManager = fm; mEnableSavedStates = enableSavedStates; } /** * Return the Fragment associated with a specified position. */ public abstract Fragment getItem(int position); @Override public void startUpdate(ViewGroup container) { } @Override public Object instantiateItem(ViewGroup container, int position) { // 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. final Fragment existing = mFragments.get(position); if (existing != null) { return existing; } if (mCurTransaction == null) { mCurTransaction = mFragmentManager.beginTransaction(); } Fragment fragment = getItem(position); if (DEBUG) LogUtils.v(TAG, "Adding item #" + position + ": f=" + fragment); if (mEnableSavedStates && mSavedState.size() > position) { Fragment.SavedState fss = mSavedState.get(position); if (fss != null) { fragment.setInitialSavedState(fss); } } if (fragment != mCurrentPrimaryItem) { setItemVisible(fragment, false); } mFragments.put(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) LogUtils.v(TAG, "Removing item #" + position + ": f=" + object + " v=" + ((Fragment) object).getView()); if (mEnableSavedStates) { while (mSavedState.size() <= position) { mSavedState.add(null); } mSavedState.set(position, mFragmentManager.saveFragmentInstanceState(fragment)); } mFragments.delete(position); mCurTransaction.remove(fragment); } @Override public void setPrimaryItem(ViewGroup container, int position, Object object) { Fragment fragment = (Fragment) object; if (fragment != mCurrentPrimaryItem) { if (mCurrentPrimaryItem != null) { setItemVisible(mCurrentPrimaryItem, false); } if (fragment != null) { setItemVisible(fragment, 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; if (mEnableSavedStates && mSavedState.size() > 0) { state = new Bundle(); Fragment.SavedState[] fss = new Fragment.SavedState[mSavedState.size()]; mSavedState.toArray(fss); state.putParcelableArray("states", fss); } for (int i = 0; i < mFragments.size(); i++) { final int pos = mFragments.keyAt(i); final Fragment f = mFragments.valueAt(i); if (state == null) { state = new Bundle(); } String key = "f" + pos; 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); mFragments.clear(); if (mEnableSavedStates) { Parcelable[] fss = bundle.getParcelableArray("states"); mSavedState.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) { setItemVisible(f, false); mFragments.put(index, f); } else { LogUtils.w(TAG, "Bad fragment at key " + key); } } } } } public void setItemVisible(Fragment item, boolean visible) { FragmentCompat.setMenuVisibility(item, visible); FragmentCompat.setUserVisibleHint(item, visible); } @Override public void notifyDataSetChanged() { // update positions in mFragments SparseArrayCompat<Fragment> newFragments = new SparseArrayCompat<Fragment>(mFragments.size()); for (int i = 0; i < mFragments.size(); i++) { final int oldPos = mFragments.keyAt(i); final Fragment f = mFragments.valueAt(i); final int newPos = getItemPosition(f); if (newPos != POSITION_NONE) { final int pos = (newPos >= 0) ? newPos : oldPos; newFragments.put(pos, f); } } mFragments = newFragments; super.notifyDataSetChanged(); } public Fragment getFragmentAt(int position) { return mFragments.get(position); } }