| 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 | |
| 17 | package android.support.v2.content; |
| 18 | |
| 19 | import android.content.Context; |
| 20 | import android.database.ContentObserver; |
| 21 | import android.os.Handler; |
| 22 | import android.support.v2.util.DebugUtils; |
| 23 | |
| 24 | import java.io.FileDescriptor; |
| 25 | import java.io.PrintWriter; |
| 26 | |
| 27 | /** |
| 28 | * Static library support version of the framework's {@link android.content.Loader}. |
| 29 | * Used to write apps that run on platforms prior to Android 3.0. When running |
| 30 | * on Android 3.0 or above, this implementation is still used; it does not try |
| 31 | * to switch to the framework's implementation. See the framework SDK |
| 32 | * documentation for a class overview. |
| 33 | */ |
| 34 | public class Loader<D> { |
| 35 | int mId; |
| 36 | OnLoadCompleteListener<D> mListener; |
| 37 | Context mContext; |
| 38 | boolean mStarted = false; |
| 39 | boolean mAbandoned = false; |
| 40 | boolean mReset = true; |
| 41 | boolean mContentChanged = false; |
| 42 | |
| 43 | public final class ForceLoadContentObserver extends ContentObserver { |
| 44 | public ForceLoadContentObserver() { |
| 45 | super(new Handler()); |
| 46 | } |
| 47 | |
| 48 | @Override |
| 49 | public boolean deliverSelfNotifications() { |
| 50 | return true; |
| 51 | } |
| 52 | |
| 53 | @Override |
| 54 | public void onChange(boolean selfChange) { |
| 55 | onContentChanged(); |
| 56 | } |
| 57 | } |
| 58 | |
| 59 | public interface OnLoadCompleteListener<D> { |
| 60 | /** |
| 61 | * Called on the thread that created the Loader when the load is complete. |
| 62 | * |
| 63 | * @param loader the loader that completed the load |
| 64 | * @param data the result of the load |
| 65 | */ |
| 66 | public void onLoadComplete(Loader<D> loader, D data); |
| 67 | } |
| 68 | |
| 69 | /** |
| 70 | * Stores away the application context associated with context. Since Loaders can be used |
| 71 | * across multiple activities it's dangerous to store the context directly. |
| 72 | * |
| 73 | * @param context used to retrieve the application context. |
| 74 | */ |
| 75 | public Loader(Context context) { |
| 76 | mContext = context.getApplicationContext(); |
| 77 | } |
| 78 | |
| 79 | /** |
| 80 | * Sends the result of the load to the registered listener. Should only be called by subclasses. |
| 81 | * |
| 82 | * Must be called from the process's main thread. |
| 83 | * |
| 84 | * @param data the result of the load |
| 85 | */ |
| 86 | public void deliverResult(D data) { |
| 87 | if (mListener != null) { |
| 88 | mListener.onLoadComplete(this, data); |
| 89 | } |
| 90 | } |
| 91 | |
| 92 | /** |
| 93 | * @return an application context retrieved from the Context passed to the constructor. |
| 94 | */ |
| 95 | public Context getContext() { |
| 96 | return mContext; |
| 97 | } |
| 98 | |
| 99 | /** |
| 100 | * @return the ID of this loader |
| 101 | */ |
| 102 | public int getId() { |
| 103 | return mId; |
| 104 | } |
| 105 | |
| 106 | /** |
| 107 | * Registers a class that will receive callbacks when a load is complete. |
| 108 | * The callback will be called on the process's main thread so it's safe to |
| 109 | * pass the results to widgets. |
| 110 | * |
| 111 | * <p>Must be called from the process's main thread. |
| 112 | */ |
| 113 | public void registerListener(int id, OnLoadCompleteListener<D> listener) { |
| 114 | if (mListener != null) { |
| 115 | throw new IllegalStateException("There is already a listener registered"); |
| 116 | } |
| 117 | mListener = listener; |
| 118 | mId = id; |
| 119 | } |
| 120 | |
| 121 | /** |
| 122 | * Remove a listener that was previously added with {@link #registerListener}. |
| 123 | * |
| 124 | * Must be called from the process's main thread. |
| 125 | */ |
| 126 | public void unregisterListener(OnLoadCompleteListener<D> listener) { |
| 127 | if (mListener == null) { |
| 128 | throw new IllegalStateException("No listener register"); |
| 129 | } |
| 130 | if (mListener != listener) { |
| 131 | throw new IllegalArgumentException("Attempting to unregister the wrong listener"); |
| 132 | } |
| 133 | mListener = null; |
| 134 | } |
| 135 | |
| 136 | /** |
| 137 | * Return whether this load has been started. That is, its {@link #startLoading()} |
| 138 | * has been called and no calls to {@link #stopLoading()} or |
| 139 | * {@link #reset()} have yet been made. |
| 140 | */ |
| 141 | public boolean isStarted() { |
| 142 | return mStarted; |
| 143 | } |
| 144 | |
| 145 | /** |
| 146 | * Return whether this loader has been abandoned. In this state, the |
| 147 | * loader <em>must not</em> report any new data, and <em>must</em> keep |
| 148 | * its last reported data valid until it is finally reset. |
| 149 | */ |
| 150 | public boolean isAbandoned() { |
| 151 | return mAbandoned; |
| 152 | } |
| 153 | |
| 154 | /** |
| 155 | * Return whether this load has been reset. That is, either the loader |
| 156 | * has not yet been started for the first time, or its {@link #reset()} |
| 157 | * has been called. |
| 158 | */ |
| 159 | public boolean isReset() { |
| 160 | return mReset; |
| 161 | } |
| 162 | |
| 163 | /** |
| 164 | * Starts an asynchronous load of the Loader's data. When the result |
| 165 | * is ready the callbacks will be called on the process's main thread. |
| 166 | * If a previous load has been completed and is still valid |
| 167 | * the result may be passed to the callbacks immediately. |
| 168 | * The loader will monitor the source of |
| 169 | * the data set and may deliver future callbacks if the source changes. |
| 170 | * Calling {@link #stopLoading} will stop the delivery of callbacks. |
| 171 | * |
| 172 | * <p>This updates the Loader's internal state so that |
| 173 | * {@link #isStarted()} and {@link #isReset()} will return the correct |
| 174 | * values, and then calls the implementation's {@link #onStartLoading()}. |
| 175 | * |
| 176 | * <p>Must be called from the process's main thread. |
| 177 | */ |
| 178 | public final void startLoading() { |
| 179 | mStarted = true; |
| 180 | mReset = false; |
| 181 | mAbandoned = false; |
| 182 | onStartLoading(); |
| 183 | } |
| 184 | |
| 185 | /** |
| 186 | * Subclasses must implement this to take care of loading their data, |
| 187 | * as per {@link #startLoading()}. This is not called by clients directly, |
| 188 | * but as a result of a call to {@link #startLoading()}. |
| 189 | */ |
| 190 | protected void onStartLoading() { |
| 191 | } |
| 192 | |
| 193 | /** |
| 194 | * Force an asynchronous load. Unlike {@link #startLoading()} this will ignore a previously |
| 195 | * loaded data set and load a new one. This simply calls through to the |
| 196 | * implementation's {@link #onForceLoad()}. You generally should only call this |
| 197 | * when the loader is started -- that is, {@link #isStarted()} returns true. |
| 198 | * |
| 199 | * <p>Must be called from the process's main thread. |
| 200 | */ |
| 201 | public void forceLoad() { |
| 202 | onForceLoad(); |
| 203 | } |
| 204 | |
| 205 | /** |
| 206 | * Subclasses must implement this to take care of requests to {@link #forceLoad()}. |
| 207 | * This will always be called from the process's main thread. |
| 208 | */ |
| 209 | protected void onForceLoad() { |
| 210 | } |
| 211 | |
| 212 | /** |
| 213 | * Stops delivery of updates until the next time {@link #startLoading()} is called. |
| 214 | * Implementations should <em>not</em> invalidate their data at this point -- |
| 215 | * clients are still free to use the last data the loader reported. They will, |
| 216 | * however, typically stop reporting new data if the data changes; they can |
| 217 | * still monitor for changes, but must not report them to the client until and |
| 218 | * if {@link #startLoading()} is later called. |
| 219 | * |
| 220 | * <p>This updates the Loader's internal state so that |
| 221 | * {@link #isStarted()} will return the correct |
| 222 | * value, and then calls the implementation's {@link #onStopLoading()}. |
| 223 | * |
| 224 | * <p>Must be called from the process's main thread. |
| 225 | */ |
| 226 | public void stopLoading() { |
| 227 | mStarted = false; |
| 228 | onStopLoading(); |
| 229 | } |
| 230 | |
| 231 | /** |
| 232 | * Subclasses must implement this to take care of stopping their loader, |
| 233 | * as per {@link #stopLoading()}. This is not called by clients directly, |
| 234 | * but as a result of a call to {@link #stopLoading()}. |
| 235 | * This will always be called from the process's main thread. |
| 236 | */ |
| 237 | protected void onStopLoading() { |
| 238 | } |
| 239 | |
| 240 | /** |
| 241 | * Tell the Loader that it is being abandoned. This is called prior |
| 242 | * to {@link #reset} to have it retain its current data but not report |
| 243 | * any new data. |
| 244 | */ |
| 245 | public void abandon() { |
| 246 | mAbandoned = true; |
| 247 | onAbandon(); |
| 248 | } |
| 249 | |
| 250 | /** |
| 251 | * Subclasses implement this to take care of being abandoned. This is |
| 252 | * an optional intermediate state prior to {@link #onReset()} -- it means that |
| 253 | * the client is no longer interested in any new data from the loader, |
| 254 | * so the loader must not report any further updates. However, the |
| 255 | * loader <em>must</em> keep its last reported data valid until the final |
| 256 | * {@link #onReset()} happens. You can retrieve the current abandoned |
| 257 | * state with {@link #isAbandoned}. |
| 258 | */ |
| 259 | protected void onAbandon() { |
| 260 | } |
| 261 | |
| 262 | /** |
| 263 | * Resets the state of the Loader. The Loader should at this point free |
| 264 | * all of its resources, since it may never be called again; however, its |
| 265 | * {@link #startLoading()} may later be called at which point it must be |
| 266 | * able to start running again. |
| 267 | * |
| 268 | * <p>This updates the Loader's internal state so that |
| 269 | * {@link #isStarted()} and {@link #isReset()} will return the correct |
| 270 | * values, and then calls the implementation's {@link #onReset()}. |
| 271 | * |
| 272 | * <p>Must be called from the process's main thread. |
| 273 | */ |
| 274 | public void reset() { |
| 275 | onReset(); |
| 276 | mReset = true; |
| 277 | mStarted = false; |
| 278 | mAbandoned = false; |
| 279 | mContentChanged = false; |
| 280 | } |
| 281 | |
| 282 | /** |
| 283 | * Subclasses must implement this to take care of resetting their loader, |
| 284 | * as per {@link #reset()}. This is not called by clients directly, |
| 285 | * but as a result of a call to {@link #reset()}. |
| 286 | * This will always be called from the process's main thread. |
| 287 | */ |
| 288 | protected void onReset() { |
| 289 | } |
| 290 | |
| 291 | /** |
| 292 | * Take the current flag indicating whether the loader's content had |
| 293 | * changed while it was stopped. If it had, true is returned and the |
| 294 | * flag is cleared. |
| 295 | */ |
| 296 | public boolean takeContentChanged() { |
| 297 | boolean res = mContentChanged; |
| 298 | mContentChanged = false; |
| 299 | return res; |
| 300 | } |
| 301 | |
| 302 | /** |
| 303 | * Called when {@link ForceLoadContentObserver} detects a change. The |
| 304 | * default implementation checks to see if the loader is currently started; |
| 305 | * if so, it simply calls {@link #forceLoad()}; otherwise, it sets a flag |
| 306 | * so that {@link #takeContentChanged()} returns true. |
| 307 | * |
| 308 | * <p>Must be called from the process's main thread. |
| 309 | */ |
| 310 | public void onContentChanged() { |
| 311 | if (mStarted) { |
| 312 | forceLoad(); |
| 313 | } else { |
| 314 | // This loader has been stopped, so we don't want to load |
| 315 | // new data right now... but keep track of it changing to |
| 316 | // refresh later if we start again. |
| 317 | mContentChanged = true; |
| 318 | } |
| 319 | } |
| 320 | |
| 321 | /** |
| 322 | * For debugging, converts an instance of the Loader's data class to |
| 323 | * a string that can be printed. Must handle a null data. |
| 324 | */ |
| 325 | public String dataToString(D data) { |
| 326 | StringBuilder sb = new StringBuilder(64); |
| 327 | DebugUtils.buildShortClassTag(data, sb); |
| 328 | sb.append("}"); |
| 329 | return sb.toString(); |
| 330 | } |
| 331 | |
| 332 | @Override |
| 333 | public String toString() { |
| 334 | StringBuilder sb = new StringBuilder(64); |
| 335 | DebugUtils.buildShortClassTag(this, sb); |
| 336 | sb.append(" id="); |
| 337 | sb.append(mId); |
| 338 | sb.append("}"); |
| 339 | return sb.toString(); |
| 340 | } |
| 341 | |
| 342 | /** |
| 343 | * Print the Loader's state into the given stream. |
| 344 | * |
| 345 | * @param prefix Text to print at the front of each line. |
| 346 | * @param fd The raw file descriptor that the dump is being sent to. |
| 347 | * @param writer A PrintWriter to which the dump is to be set. |
| 348 | * @param args Additional arguments to the dump request. |
| 349 | */ |
| 350 | public void dump(String prefix, FileDescriptor fd, PrintWriter writer, String[] args) { |
| 351 | writer.print(prefix); writer.print("mId="); writer.print(mId); |
| 352 | writer.print(" mListener="); writer.println(mListener); |
| 353 | writer.print(prefix); writer.print("mStarted="); writer.print(mStarted); |
| 354 | writer.print(" mContentChanged="); writer.print(mContentChanged); |
| 355 | writer.print(" mAbandoned="); writer.print(mAbandoned); |
| 356 | writer.print(" mReset="); writer.println(mReset); |
| 357 | } |
| 358 | } |