Java tutorial
package am.util.viewpager.adapter; /* * 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. */ 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.FragmentStatePagerAdapter; 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; /** * Implementation of {@link PagerAdapter} that * represents each page as a {@link Fragment} that is persistently * kept in the fragment manager as long as the user can return to the page. * <p> * <p>This version of the pager is best for use when there are a handful of * typically more static fragments to be paged through, such as a set of tabs. * The fragment of each page the user visits will be kept in memory, though its * view hierarchy may be destroyed when not visible. This can result in using * a significant amount of memory since fragment instances can hold on to an * arbitrary amount of state. For larger sets of pages, consider * {@link FragmentStatePagerAdapter}. * <p> * <p>When using FragmentPagerAdapter the host ViewPager must have a * valid ID set.</p> * <p> * <p>Subclasses only need to implement {@link #getItem(int)} * and {@link #getCount()} to have a working adapter. * <p> * <p>Here is an example implementation of a pager containing fragments of * lists: * <p> * {@sample frameworks/support/samples/Support4Demos/src/com/example/android/supportv4/app/FragmentPagerSupport.java * complete} * <p> * <p>The <code>R.layout.fragment_pager</code> resource of the top-level fragment is: * <p> * {@sample frameworks/support/samples/Support4Demos/res/layout/fragment_pager.xml * complete} * <p> * <p>The <code>R.layout.fragment_pager_list</code> resource containing each * individual fragment's layout is: * <p> * {@sample frameworks/support/samples/Support4Demos/res/layout/fragment_pager_list.xml * complete} */ @SuppressWarnings("all") public abstract class FragmentRemovePagerAdapter extends PagerAdapter { private static final String TAG = FragmentRemovePagerAdapter.class.getSimpleName(); private static final boolean DEBUG = false; private final FragmentManager mFragmentManager; private FragmentTransaction mCurTransaction = null; private ArrayList<Fragment.SavedState> mSavedState = new ArrayList<>(); private Fragment mCurrentPrimaryItem = null; private int mViewGroupId; public FragmentRemovePagerAdapter(FragmentManager fm) { mFragmentManager = fm; } /** * Return the Fragment associated with a specified position. */ public abstract Fragment getItem(int position); @Override public void startUpdate(ViewGroup container) { mViewGroupId = container.getId(); if (mViewGroupId == View.NO_ID) { throw new IllegalStateException("ViewPager with adapter " + this + " requires a view id"); } } @Override public Object instantiateItem(ViewGroup container, int position) { if (mCurTransaction == null) { mCurTransaction = mFragmentManager.beginTransaction(); } final long itemId = getItemId(position); // Do we already have this fragment? String name = makeFragmentName(container.getId(), itemId); Fragment fragment = mFragmentManager.findFragmentByTag(name); if (fragment != null) { if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment); mCurTransaction.attach(fragment); } else { fragment = getItem(position); if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment); if (mSavedState.size() > position) { Fragment.SavedState fss = mSavedState.get(position); if (fss != null) { fragment.setInitialSavedState(fss); } } mCurTransaction.add(container.getId(), fragment, makeFragmentName(container.getId(), itemId)); } if (fragment != mCurrentPrimaryItem) { fragment.setMenuVisibility(false); fragment.setUserVisibleHint(false); } return fragment; } @Override public void destroyItem(ViewGroup container, int position, Object object) { if (mCurTransaction == null) { mCurTransaction = mFragmentManager.beginTransaction(); } if (DEBUG) Log.v(TAG, "Detaching item #" + getItemId(position) + ": f=" + object + " v=" + ((Fragment) object).getView()); mCurTransaction.detach((Fragment) object); } @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.commitNowAllowingStateLoss(); mCurTransaction = null; } } @Override public boolean isViewFromObject(View view, Object object) { return ((Fragment) object).getView() == view; } @Override public Parcelable saveState() { Bundle state = null; if (mSavedState.size() > 0) { state = new Bundle(); Fragment.SavedState[] fss = new Fragment.SavedState[mSavedState.size()]; mSavedState.toArray(fss); state.putParcelableArray("states", fss); } final int count = getCount(); for (int position = 0; position < count; position++) { final long itemId = getItemId(position); String name = makeFragmentName(mViewGroupId, itemId); Fragment fragment = mFragmentManager.findFragmentByTag(name); if (fragment != null && fragment.isAdded()) { if (state == null) { state = new Bundle(); } String key = "f" + itemId; mFragmentManager.putFragment(state, key, fragment); } } return state; } @Override public void restoreState(Parcelable state, ClassLoader loader) { if (state != null) { Bundle bundle = (Bundle) state; bundle.setClassLoader(loader); 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")) { Fragment f = mFragmentManager.getFragment(bundle, key); if (f != null) { f.setMenuVisibility(false); } else { Log.w(TAG, "Bad fragment at key " + key); } } } } } /** * Return a unique identifier for the item at the given position. * <p> * <p>The default implementation returns the given position. * Subclasses should override this method if the positions of items can change.</p> * * @param position Position within this adapter * @return Unique identifier for the item at position */ public long getItemId(int position) { return position; } private static String makeFragmentName(int viewId, long id) { return "android:switcher:" + viewId + ":" + id; } /** * Remove all item */ public void removeAll() { if (mCurTransaction == null) { mCurTransaction = mFragmentManager.beginTransaction(); } final int count = getCount(); for (int position = 0; position < count; position++) { final long itemId = getItemId(position); String name = makeFragmentName(mViewGroupId, itemId); Fragment fragment = mFragmentManager.findFragmentByTag(name); if (fragment == null) continue; if (DEBUG) Log.v(TAG, "Detaching item #" + itemId + ": f=" + fragment + " v=" + fragment.getView()); while (mSavedState.size() <= getCount()) { mSavedState.add(null); } mSavedState.set(position, fragment.isAdded() ? mFragmentManager.saveFragmentInstanceState(fragment) : null); mCurTransaction.remove(fragment); } mCurTransaction.commitNowAllowingStateLoss(); mCurTransaction = null; } }