FragmentPagerAdapter.java revision 2d0f75424d03e9c54ff733aedda4382c49c27d36
1/* 2 * Copyright (C) 2011 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17package android.support.v13.app; 18 19import android.app.Fragment; 20import android.app.FragmentManager; 21import android.app.FragmentTransaction; 22import android.os.Parcelable; 23import android.support.v4.app.FragmentStatePagerAdapter; 24import android.support.v4.view.PagerAdapter; 25import android.util.Log; 26import android.view.View; 27import android.view.ViewGroup; 28 29/** 30 * Implementation of {@link android.support.v4.view.PagerAdapter} that 31 * represents each page as a {@link android.app.Fragment} that is persistently 32 * kept in the fragment manager as long as the user can return to the page. 33 * 34 * <p>This version of the pager is best for use when there are a handful of 35 * typically more static fragments to be paged through, such as a set of tabs. 36 * The fragment of each page the user visits will be kept in memory, though its 37 * view hierarchy may be destroyed when not visible. This can result in using 38 * a significant amount of memory since fragment instances can hold on to an 39 * arbitrary amount of state. For larger sets of pages, consider 40 * {@link FragmentStatePagerAdapter}. 41 * 42 * <p>When using FragmentPagerAdapter the host ViewPager must have a 43 * valid ID set.</p> 44 * 45 * <p>Subclasses only need to implement {@link #getItem(int)} 46 * and {@link #getCount()} to have a working adapter. 47 * 48 * <p>Here is an example implementation of a pager containing fragments of 49 * lists: 50 * 51 * {@sample frameworks/support/samples/Support13Demos/src/com/example/android/supportv13/app/FragmentPagerSupport.java 52 * complete} 53 * 54 * <p>The <code>R.layout.fragment_pager</code> resource of the top-level fragment is: 55 * 56 * {@sample frameworks/support/samples/Support13Demos/res/layout/fragment_pager.xml 57 * complete} 58 * 59 * <p>The <code>R.layout.fragment_pager_list</code> resource containing each 60 * individual fragment's layout is: 61 * 62 * {@sample frameworks/support/samples/Support13Demos/res/layout/fragment_pager_list.xml 63 * complete} 64 */ 65public abstract class FragmentPagerAdapter extends PagerAdapter { 66 private static final String TAG = "FragmentPagerAdapter"; 67 private static final boolean DEBUG = false; 68 69 private final FragmentManager mFragmentManager; 70 private FragmentTransaction mCurTransaction = null; 71 private Fragment mCurrentPrimaryItem = null; 72 73 public FragmentPagerAdapter(FragmentManager fm) { 74 mFragmentManager = fm; 75 } 76 77 /** 78 * Return the Fragment associated with a specified position. 79 */ 80 public abstract Fragment getItem(int position); 81 82 @Override 83 public void startUpdate(ViewGroup container) { 84 if (container.getId() == View.NO_ID) { 85 throw new IllegalStateException("ViewPager with adapter " + this 86 + " requires a view id"); 87 } 88 } 89 90 @Override 91 public Object instantiateItem(ViewGroup container, int position) { 92 if (mCurTransaction == null) { 93 mCurTransaction = mFragmentManager.beginTransaction(); 94 } 95 96 final long itemId = getItemId(position); 97 98 // Do we already have this fragment? 99 String name = makeFragmentName(container.getId(), itemId); 100 Fragment fragment = mFragmentManager.findFragmentByTag(name); 101 if (fragment != null) { 102 if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment); 103 mCurTransaction.attach(fragment); 104 } else { 105 fragment = getItem(position); 106 if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment); 107 mCurTransaction.add(container.getId(), fragment, 108 makeFragmentName(container.getId(), itemId)); 109 } 110 if (fragment != mCurrentPrimaryItem) { 111 fragment.setMenuVisibility(false); 112 FragmentCompat.setUserVisibleHint(fragment, false); 113 } 114 115 return fragment; 116 } 117 118 @Override 119 public void destroyItem(ViewGroup container, int position, Object object) { 120 if (mCurTransaction == null) { 121 mCurTransaction = mFragmentManager.beginTransaction(); 122 } 123 if (DEBUG) Log.v(TAG, "Detaching item #" + getItemId(position) + ": f=" + object 124 + " v=" + ((Fragment)object).getView()); 125 mCurTransaction.detach((Fragment)object); 126 } 127 128 @Override 129 public void setPrimaryItem(ViewGroup container, int position, Object object) { 130 Fragment fragment = (Fragment)object; 131 if (fragment != mCurrentPrimaryItem) { 132 if (mCurrentPrimaryItem != null) { 133 mCurrentPrimaryItem.setMenuVisibility(false); 134 FragmentCompat.setUserVisibleHint(mCurrentPrimaryItem, false); 135 } 136 if (fragment != null) { 137 fragment.setMenuVisibility(true); 138 FragmentCompat.setUserVisibleHint(fragment, true); 139 } 140 mCurrentPrimaryItem = fragment; 141 } 142 } 143 144 @Override 145 public void finishUpdate(ViewGroup container) { 146 if (mCurTransaction != null) { 147 mCurTransaction.commitAllowingStateLoss(); 148 mCurTransaction = null; 149 mFragmentManager.executePendingTransactions(); 150 } 151 } 152 153 @Override 154 public boolean isViewFromObject(View view, Object object) { 155 return ((Fragment)object).getView() == view; 156 } 157 158 @Override 159 public Parcelable saveState() { 160 return null; 161 } 162 163 @Override 164 public void restoreState(Parcelable state, ClassLoader loader) { 165 } 166 167 /** 168 * Return a unique identifier for the item at the given position. 169 * 170 * <p>The default implementation returns the given position. 171 * Subclasses should override this method if the positions of items can change.</p> 172 * 173 * @param position Position within this adapter 174 * @return Unique identifier for the item at position 175 */ 176 public long getItemId(int position) { 177 return position; 178 } 179 180 private static String makeFragmentName(int viewId, long id) { 181 return "android:switcher:" + viewId + ":" + id; 182 } 183}