1 /* 2 * Copyright (C) 2015 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 17 package com.android.internal.widget; 18 19 import android.database.DataSetObservable; 20 import android.database.DataSetObserver; 21 import android.os.Parcelable; 22 import android.view.View; 23 import android.view.ViewGroup; 24 25 /** 26 * Base class providing the adapter to populate pages inside of 27 * a {@link android.support.v4.view.ViewPager}. You will most likely want to use a more 28 * specific implementation of this, such as 29 * {@link android.support.v4.app.FragmentPagerAdapter} or 30 * {@link android.support.v4.app.FragmentStatePagerAdapter}. 31 * 32 * <p>When you implement a PagerAdapter, you must override the following methods 33 * at minimum:</p> 34 * <ul> 35 * <li>{@link #instantiateItem(android.view.ViewGroup, int)}</li> 36 * <li>{@link #destroyItem(android.view.ViewGroup, int, Object)}</li> 37 * <li>{@link #getCount()}</li> 38 * <li>{@link #isViewFromObject(android.view.View, Object)}</li> 39 * </ul> 40 * 41 * <p>PagerAdapter is more general than the adapters used for 42 * {@link android.widget.AdapterView AdapterViews}. Instead of providing a 43 * View recycling mechanism directly ViewPager uses callbacks to indicate the 44 * steps taken during an update. A PagerAdapter may implement a form of View 45 * recycling if desired or use a more sophisticated method of managing page 46 * Views such as Fragment transactions where each page is represented by its 47 * own Fragment.</p> 48 * 49 * <p>ViewPager associates each page with a key Object instead of working with 50 * Views directly. This key is used to track and uniquely identify a given page 51 * independent of its position in the adapter. A call to the PagerAdapter method 52 * {@link #startUpdate(android.view.ViewGroup)} indicates that the contents of the ViewPager 53 * are about to change. One or more calls to {@link #instantiateItem(android.view.ViewGroup, int)} 54 * and/or {@link #destroyItem(android.view.ViewGroup, int, Object)} will follow, and the end 55 * of an update will be signaled by a call to {@link #finishUpdate(android.view.ViewGroup)}. 56 * By the time {@link #finishUpdate(android.view.ViewGroup) finishUpdate} returns the views 57 * associated with the key objects returned by 58 * {@link #instantiateItem(android.view.ViewGroup, int) instantiateItem} should be added to 59 * the parent ViewGroup passed to these methods and the views associated with 60 * the keys passed to {@link #destroyItem(android.view.ViewGroup, int, Object) destroyItem} 61 * should be removed. The method {@link #isViewFromObject(android.view.View, Object)} identifies 62 * whether a page View is associated with a given key object.</p> 63 * 64 * <p>A very simple PagerAdapter may choose to use the page Views themselves 65 * as key objects, returning them from {@link #instantiateItem(android.view.ViewGroup, int)} 66 * after creation and adding them to the parent ViewGroup. A matching 67 * {@link #destroyItem(android.view.ViewGroup, int, Object)} implementation would remove the 68 * View from the parent ViewGroup and {@link #isViewFromObject(android.view.View, Object)} 69 * could be implemented as <code>return view == object;</code>.</p> 70 * 71 * <p>PagerAdapter supports data set changes. Data set changes must occur on the 72 * main thread and must end with a call to {@link #notifyDataSetChanged()} similar 73 * to AdapterView adapters derived from {@link android.widget.BaseAdapter}. A data 74 * set change may involve pages being added, removed, or changing position. The 75 * ViewPager will keep the current page active provided the adapter implements 76 * the method {@link #getItemPosition(Object)}.</p> 77 */ 78 public abstract class PagerAdapter { 79 private DataSetObservable mObservable = new DataSetObservable(); 80 81 public static final int POSITION_UNCHANGED = -1; 82 public static final int POSITION_NONE = -2; 83 84 /** 85 * Return the number of views available. 86 */ getCount()87 public abstract int getCount(); 88 89 /** 90 * Called when a change in the shown pages is going to start being made. 91 * @param container The containing View which is displaying this adapter's 92 * page views. 93 */ startUpdate(ViewGroup container)94 public void startUpdate(ViewGroup container) { 95 startUpdate((View) container); 96 } 97 98 /** 99 * Create the page for the given position. The adapter is responsible 100 * for adding the view to the container given here, although it only 101 * must ensure this is done by the time it returns from 102 * {@link #finishUpdate(android.view.ViewGroup)}. 103 * 104 * @param container The containing View in which the page will be shown. 105 * @param position The page position to be instantiated. 106 * @return Returns an Object representing the new page. This does not 107 * need to be a View, but can be some other container of the page. 108 */ instantiateItem(ViewGroup container, int position)109 public Object instantiateItem(ViewGroup container, int position) { 110 return instantiateItem((View) container, position); 111 } 112 113 /** 114 * Remove a page for the given position. The adapter is responsible 115 * for removing the view from its container, although it only must ensure 116 * this is done by the time it returns from {@link #finishUpdate(android.view.ViewGroup)}. 117 * 118 * @param container The containing View from which the page will be removed. 119 * @param position The page position to be removed. 120 * @param object The same object that was returned by 121 * {@link #instantiateItem(android.view.View, int)}. 122 */ destroyItem(ViewGroup container, int position, Object object)123 public void destroyItem(ViewGroup container, int position, Object object) { 124 destroyItem((View) container, position, object); 125 } 126 127 /** 128 * Called to inform the adapter of which item is currently considered to 129 * be the "primary", that is the one show to the user as the current page. 130 * 131 * @param container The containing View from which the page will be removed. 132 * @param position The page position that is now the primary. 133 * @param object The same object that was returned by 134 * {@link #instantiateItem(android.view.View, int)}. 135 */ setPrimaryItem(ViewGroup container, int position, Object object)136 public void setPrimaryItem(ViewGroup container, int position, Object object) { 137 setPrimaryItem((View) container, position, object); 138 } 139 140 /** 141 * Called when the a change in the shown pages has been completed. At this 142 * point you must ensure that all of the pages have actually been added or 143 * removed from the container as appropriate. 144 * @param container The containing View which is displaying this adapter's 145 * page views. 146 */ finishUpdate(ViewGroup container)147 public void finishUpdate(ViewGroup container) { 148 finishUpdate((View) container); 149 } 150 151 /** 152 * Called when a change in the shown pages is going to start being made. 153 * @param container The containing View which is displaying this adapter's 154 * page views. 155 * 156 * @deprecated Use {@link #startUpdate(android.view.ViewGroup)} 157 */ startUpdate(View container)158 public void startUpdate(View container) { 159 } 160 161 /** 162 * Create the page for the given position. The adapter is responsible 163 * for adding the view to the container given here, although it only 164 * must ensure this is done by the time it returns from 165 * {@link #finishUpdate(android.view.ViewGroup)}. 166 * 167 * @param container The containing View in which the page will be shown. 168 * @param position The page position to be instantiated. 169 * @return Returns an Object representing the new page. This does not 170 * need to be a View, but can be some other container of the page. 171 * 172 * @deprecated Use {@link #instantiateItem(android.view.ViewGroup, int)} 173 */ instantiateItem(View container, int position)174 public Object instantiateItem(View container, int position) { 175 throw new UnsupportedOperationException( 176 "Required method instantiateItem was not overridden"); 177 } 178 179 /** 180 * Remove a page for the given position. The adapter is responsible 181 * for removing the view from its container, although it only must ensure 182 * this is done by the time it returns from {@link #finishUpdate(android.view.View)}. 183 * 184 * @param container The containing View from which the page will be removed. 185 * @param position The page position to be removed. 186 * @param object The same object that was returned by 187 * {@link #instantiateItem(android.view.View, int)}. 188 * 189 * @deprecated Use {@link #destroyItem(android.view.ViewGroup, int, Object)} 190 */ destroyItem(View container, int position, Object object)191 public void destroyItem(View container, int position, Object object) { 192 throw new UnsupportedOperationException("Required method destroyItem was not overridden"); 193 } 194 195 /** 196 * Called to inform the adapter of which item is currently considered to 197 * be the "primary", that is the one show to the user as the current page. 198 * 199 * @param container The containing View from which the page will be removed. 200 * @param position The page position that is now the primary. 201 * @param object The same object that was returned by 202 * {@link #instantiateItem(android.view.View, int)}. 203 * 204 * @deprecated Use {@link #setPrimaryItem(android.view.ViewGroup, int, Object)} 205 */ setPrimaryItem(View container, int position, Object object)206 public void setPrimaryItem(View container, int position, Object object) { 207 } 208 209 /** 210 * Called when the a change in the shown pages has been completed. At this 211 * point you must ensure that all of the pages have actually been added or 212 * removed from the container as appropriate. 213 * @param container The containing View which is displaying this adapter's 214 * page views. 215 * 216 * @deprecated Use {@link #finishUpdate(android.view.ViewGroup)} 217 */ finishUpdate(View container)218 public void finishUpdate(View container) { 219 } 220 221 /** 222 * Determines whether a page View is associated with a specific key object 223 * as returned by {@link #instantiateItem(android.view.ViewGroup, int)}. This method is 224 * required for a PagerAdapter to function properly. 225 * 226 * @param view Page View to check for association with <code>object</code> 227 * @param object Object to check for association with <code>view</code> 228 * @return true if <code>view</code> is associated with the key object <code>object</code> 229 */ isViewFromObject(View view, Object object)230 public abstract boolean isViewFromObject(View view, Object object); 231 232 /** 233 * Save any instance state associated with this adapter and its pages that should be 234 * restored if the current UI state needs to be reconstructed. 235 * 236 * @return Saved state for this adapter 237 */ saveState()238 public Parcelable saveState() { 239 return null; 240 } 241 242 /** 243 * Restore any instance state associated with this adapter and its pages 244 * that was previously saved by {@link #saveState()}. 245 * 246 * @param state State previously saved by a call to {@link #saveState()} 247 * @param loader A ClassLoader that should be used to instantiate any restored objects 248 */ restoreState(Parcelable state, ClassLoader loader)249 public void restoreState(Parcelable state, ClassLoader loader) { 250 } 251 252 /** 253 * Called when the host view is attempting to determine if an item's position 254 * has changed. Returns {@link #POSITION_UNCHANGED} if the position of the given 255 * item has not changed or {@link #POSITION_NONE} if the item is no longer present 256 * in the adapter. 257 * 258 * <p>The default implementation assumes that items will never 259 * change position and always returns {@link #POSITION_UNCHANGED}. 260 * 261 * @param object Object representing an item, previously returned by a call to 262 * {@link #instantiateItem(android.view.View, int)}. 263 * @return object's new position index from [0, {@link #getCount()}), 264 * {@link #POSITION_UNCHANGED} if the object's position has not changed, 265 * or {@link #POSITION_NONE} if the item is no longer present. 266 */ getItemPosition(Object object)267 public int getItemPosition(Object object) { 268 return POSITION_UNCHANGED; 269 } 270 271 /** 272 * This method should be called by the application if the data backing this adapter has changed 273 * and associated views should update. 274 */ notifyDataSetChanged()275 public void notifyDataSetChanged() { 276 mObservable.notifyChanged(); 277 } 278 279 /** 280 * Register an observer to receive callbacks related to the adapter's data changing. 281 * 282 * @param observer The {@link android.database.DataSetObserver} which will receive callbacks. 283 */ registerDataSetObserver(DataSetObserver observer)284 public void registerDataSetObserver(DataSetObserver observer) { 285 mObservable.registerObserver(observer); 286 } 287 288 /** 289 * Unregister an observer from callbacks related to the adapter's data changing. 290 * 291 * @param observer The {@link android.database.DataSetObserver} which will be unregistered. 292 */ unregisterDataSetObserver(DataSetObserver observer)293 public void unregisterDataSetObserver(DataSetObserver observer) { 294 mObservable.unregisterObserver(observer); 295 } 296 297 /** 298 * This method may be called by the ViewPager to obtain a title string 299 * to describe the specified page. This method may return null 300 * indicating no title for this page. The default implementation returns 301 * null. 302 * 303 * @param position The position of the title requested 304 * @return A title for the requested page 305 */ getPageTitle(int position)306 public CharSequence getPageTitle(int position) { 307 return null; 308 } 309 310 /** 311 * Returns the proportional width of a given page as a percentage of the 312 * ViewPager's measured width from (0.f-1.f] 313 * 314 * @param position The position of the page requested 315 * @return Proportional width for the given page position 316 */ getPageWidth(int position)317 public float getPageWidth(int position) { 318 return 1.f; 319 } 320 } 321