Java tutorial
/* * Copyright 2012 Google Inc. * * 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.andreaszeiser.bob; import java.lang.ref.WeakReference; import java.util.Hashtable; import java.util.concurrent.Executor; import java.util.concurrent.Executors; import java.util.concurrent.ThreadFactory; import java.util.concurrent.atomic.AtomicInteger; import android.content.Context; import android.content.res.Resources; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.drawable.BitmapDrawable; import android.graphics.drawable.ColorDrawable; import android.graphics.drawable.Drawable; import android.graphics.drawable.TransitionDrawable; import android.os.AsyncTask; import android.support.v4.app.FragmentActivity; import android.support.v4.app.FragmentManager; import android.text.TextUtils; import android.widget.ImageView; import com.andreaszeiser.bob.utils.Log; import com.andreaszeiser.bob.utils.UIUtils; /** * This class wraps up completing some arbitrary long running work when loading * a bitmap to an ImageView. It handles things like using a memory and disk * cache, running the work in a background thread and setting a placeholder * image. */ public abstract class ImageWorker { private static final String TAG = ImageWorker.class.getSimpleName(); private static final int FADE_IN_TIME = 200; protected ImageCache mImageCache; protected ImageCache.ImageCacheParams mImageCacheParams; protected Bitmap mLoadingBitmap; protected boolean mFadeInBitmap = true; private boolean mExitTasksEarly = false; protected boolean mPauseWork = false; private final Object mPauseWorkLock = new Object(); private final Hashtable<Integer, Bitmap> loadingBitmaps = new Hashtable<Integer, Bitmap>(2); protected Resources mResources; private static final int MESSAGE_CLEAR = 0; private static final int MESSAGE_INIT_DISK_CACHE = 1; private static final int MESSAGE_FLUSH = 2; private static final int MESSAGE_CLOSE = 3; private static final ThreadFactory sThreadFactory = new ThreadFactory() { private final AtomicInteger mCount = new AtomicInteger(1); public Thread newThread(Runnable r) { return new Thread(r, "AsyncTask #" + mCount.getAndIncrement()); } }; // Dual thread executor for main AsyncTask public static final Executor DUAL_THREAD_EXECUTOR = Executors.newFixedThreadPool(2, sThreadFactory); protected ImageWorker(Context context) { mResources = context.getResources(); } /** * Load an image specified by the data parameter into an ImageView (override * {@link ImageWorker#processBitmap(Object)} to define the processing * logic). A memory and disk cache will be used if an {@link ImageCache} has * been set using {@link ImageWorker#addImageCache}. If the image is found * in the memory cache, it is set immediately, otherwise an * {@link AsyncTask} will be created to asynchronously load the bitmap. * * @param data * The URL of the image to download. * @param imageView * The ImageView to bind the downloaded image to. */ protected void loadImage(Object data, ImageView imageView) { loadImage(data, imageView, mLoadingBitmap, null); } /** * Load an image specified by the data parameter into an ImageView (override * {@link ImageWorker#processBitmap(Object)} to define the processing * logic). A memory and disk cache will be used if an {@link ImageCache} has * been set using {@link ImageWorker#addImageCache}. If the image is found * in the memory cache, it is set immediately, otherwise an * {@link AsyncTask} will be created to asynchronously load the bitmap. * * @param data * The URL of the image to download. * @param imageView * The ImageView to bind the downloaded image to. * @param resId * Resource of placeholder bitmap while the image loads. */ protected void loadImage(Object data, ImageView imageView, int resId) { if (!loadingBitmaps.containsKey(resId)) { // Store loading bitmap in a hash table to prevent continual // decoding loadingBitmaps.put(resId, BitmapFactory.decodeResource(mResources, resId)); } loadImage(data, imageView, loadingBitmaps.get(resId), null); } /** * Load an image specified by the data parameter into an ImageView (override * {@link ImageWorker#processBitmap(Object)} to define the processing * logic). A memory and disk cache will be used if an {@link ImageCache} has * been set using {@link ImageWorker#addImageCache}. If the image is found * in the memory cache, it is set immediately, otherwise an * {@link AsyncTask} will be created to asynchronously load the bitmap. * * @param data * The URL of the image to download. * @param imageView * The ImageView to bind the downloaded image to. */ public void loadImage(Object data, ImageView imageView, Bitmap loadingBitmap, ImageWorkerListener listener) { Bitmap bitmap = null; if (data == null) { // no valid url, set loading image instead bitmap = loadingBitmap; } if (bitmap == null && mImageCache != null) { bitmap = mImageCache.getBitmapFromMemCache(String.valueOf(data)); } if (bitmap != null) { // Bitmap found in memory cache if (listener == null || !listener.onImageLoaded(imageView, bitmap)) { imageView.setImageBitmap(bitmap); } } else if (cancelPotentialWork(data, imageView)) { final BitmapWorkerTask task = new BitmapWorkerTask(imageView, listener); final AsyncDrawable asyncDrawable = new AsyncDrawable(mResources, loadingBitmap, task); imageView.setImageDrawable(asyncDrawable); if (UIUtils.hasHoneycomb()) { // On HC+ we execute on a dual thread executor. There really // isn't much extra // benefit to having a really large pool of threads. Having more // than one will // likely benefit network bottlenecks though. task.executeOnExecutor(DUAL_THREAD_EXECUTOR, data); } else { // Otherwise pre-HC the default is a thread pool executor (not // ideal, serial // execution or a smaller number of threads would be better). task.execute(data); } } } /** * Tries to load bitmap from cache if {@link #mImageCache} is available. The * order of processed caches: * <ol> * <li>memory cache</li> * <li>disk cache</li> * </ol> * * @param data * @return */ public Bitmap loadImageFromCache(final String data) { if (mImageCache == null && data != null && !data.equals("")) { return null; } Bitmap bitmap = mImageCache.getBitmapFromMemCache(data); if (bitmap == null) { bitmap = mImageCache.getBitmapFromDiskCache(data); } return bitmap; } /** * Set placeholder bitmap that shows when the the background thread is * running. * * @param bitmap */ public void setLoadingImage(Bitmap bitmap) { mLoadingBitmap = bitmap; } /** * Set placeholder bitmap that shows when the the background thread is * running. * * @param resId */ public void setLoadingImage(int resId) { mLoadingBitmap = BitmapFactory.decodeResource(mResources, resId); } /** * Adds an {@link ImageCache} to this worker in the background (to prevent * disk access on UI thread). * * @param fragmentManager * The FragmentManager to initialize and add the cache * @param cacheParams * The cache parameters to use */ public void addImageCache(FragmentManager fragmentManager, ImageCache.ImageCacheParams cacheParams) { mImageCacheParams = cacheParams; setImageCache(ImageCache.findOrCreateCache(fragmentManager, mImageCacheParams)); new CacheAsyncTask().execute(MESSAGE_INIT_DISK_CACHE); } /** * Adds an {@link ImageCache} to this worker in the background (to prevent * disk access on UI thread) using default cache parameters. * * @param fragmentActivity * The FragmentActivity to initialize and add the cache */ public void addImageCache(FragmentActivity fragmentActivity) { addImageCache(fragmentActivity.getSupportFragmentManager(), new ImageCache.ImageCacheParams(fragmentActivity)); } /** * Sets the {@link ImageCache} object to use with this ImageWorker. Usually * you will not need to call this directly, instead use * {@link ImageWorker#addImageCache} which will create and add the * {@link ImageCache} object in a background thread (to ensure no disk * access on the main/UI thread). * * @param imageCache */ public void setImageCache(ImageCache imageCache) { mImageCache = imageCache; new CacheAsyncTask().execute(MESSAGE_INIT_DISK_CACHE); } /** * If set to true, the image will fade-in once it has been loaded by the * background thread. */ public void setImageFadeIn(boolean fadeIn) { mFadeInBitmap = fadeIn; } /** * Setting this to true will signal the working tasks to exit processing at * the next chance. This helps finish up pending work when the activity is * no longer in the foreground and completing the tasks is no longer useful. * * @param exitTasksEarly */ public void setExitTasksEarly(boolean exitTasksEarly) { mExitTasksEarly = exitTasksEarly; setPauseWork(false); } /** * Subclasses should override this to define any processing or work that * must happen to produce the final bitmap. This will be executed in a * background thread and be long running. For example, you could resize a * large bitmap here, or pull down an image from the network. * * @param data * The data to identify which image to process, as provided by * {@link ImageWorker#loadImage(Object, ImageView)} * @return The processed bitmap */ protected abstract Bitmap processBitmap(Object data); /** * Cancels any pending work attached to the provided ImageView. * * @param imageView */ public static void cancelWork(ImageView imageView) { final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView); if (bitmapWorkerTask != null) { bitmapWorkerTask.cancel(true); if (BuildConfig.DEBUG) { Log.v(TAG, "cancelWork - cancelled work for " + bitmapWorkerTask.data); } } } /** * Returns true if the current work has been canceled or if there was no * work in progress on this image view. Returns false if the work in * progress deals with the same data. The work is not stopped in that case. */ public static boolean cancelPotentialWork(Object data, ImageView imageView) { final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView); if (bitmapWorkerTask != null) { final Object bitmapData = bitmapWorkerTask.data; if (bitmapData == null || !bitmapData.equals(data)) { bitmapWorkerTask.cancel(true); Log.v(TAG, "cancelPotentialWork - cancelled work for " + data); } else { // The same work is already in progress. return false; } } return true; } /** * @param imageView * Any imageView * @return Retrieve the currently active work task (if any) associated with * this imageView. null if there is no such task. */ private static BitmapWorkerTask getBitmapWorkerTask(ImageView imageView) { if (imageView != null) { final Drawable drawable = imageView.getDrawable(); if (drawable instanceof AsyncDrawable) { final AsyncDrawable asyncDrawable = (AsyncDrawable) drawable; return asyncDrawable.getBitmapWorkerTask(); } } return null; } /** * The actual AsyncTask that will asynchronously process the image. */ private class BitmapWorkerTask extends AsyncTask<Object, Void, Bitmap> { private Object data; private final WeakReference<ImageView> imageViewReference; private ImageWorkerListener imageWorkerListener; public BitmapWorkerTask(ImageView imageView, ImageWorkerListener imageWorkerListener) { imageViewReference = new WeakReference<ImageView>(imageView); this.imageWorkerListener = imageWorkerListener; } /** * Background processing. */ @Override protected Bitmap doInBackground(Object... params) { Log.v(TAG, "doInBackground - starting work"); data = params[0]; final String dataString = String.valueOf(data); if (TextUtils.isEmpty(dataString)) { return null; } Bitmap bitmap = null; // Wait here if work is paused and the task is not cancelled synchronized (mPauseWorkLock) { while (mPauseWork && !isCancelled()) { try { mPauseWorkLock.wait(); } catch (InterruptedException e) { } } } // If the image cache is available and this task has not been // cancelled by another // thread and the ImageView that was originally bound to this task // is still bound back // to this task and our "exit early" flag is not set then try and // fetch the bitmap from // the cache if (mImageCache != null && !isCancelled() && getAttachedImageView() != null && !mExitTasksEarly) { bitmap = mImageCache.getBitmapFromDiskCache(dataString); } // If the bitmap was not found in the cache and this task has not // been cancelled by // another thread and the ImageView that was originally bound to // this task is still // bound back to this task and our "exit early" flag is not set, // then call the main // process method (as implemented by a subclass) if (bitmap == null && !isCancelled() && getAttachedImageView() != null && !mExitTasksEarly) { bitmap = processBitmap(params[0]); } // If the bitmap was processed and the image cache is available, // then add the processed // bitmap to the cache for future use. Note we don't check if the // task was cancelled // here, if it was, and the thread is still running, we may as well // add the processed // bitmap to our cache as it might be used again in the future if (bitmap != null && mImageCache != null) { mImageCache.addBitmapToCache(dataString, bitmap); } Log.v(TAG, "doInBackground - finished work"); return bitmap; } /** * Once the image is processed, associates it to the imageView */ @Override protected void onPostExecute(Bitmap bitmap) { // if cancel was called on this task or the "exit early" flag is set // then we're done if (isCancelled() || mExitTasksEarly) { bitmap = null; } final ImageView imageView = getAttachedImageView(); if (bitmap != null && imageView != null) { if (imageWorkerListener == null || !imageWorkerListener.onImageLoaded(imageView, bitmap)) { setImageBitmap(imageView, bitmap); } } imageWorkerListener = null; } @Override protected void onCancelled() { super.onCancelled(); synchronized (mPauseWorkLock) { mPauseWorkLock.notifyAll(); } } /** * Returns the ImageView associated with this task as long as the * ImageView's task still points to this task as well. Returns null * otherwise. */ private ImageView getAttachedImageView() { final ImageView imageView = imageViewReference.get(); final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView); if (this == bitmapWorkerTask) { return imageView; } return null; } } /** * A custom Drawable that will be attached to the imageView while the work * is in progress. Contains a reference to the actual worker task, so that * it can be stopped if a new binding is required, and makes sure that only * the last started worker process can bind its result, independently of the * finish order. */ private static class AsyncDrawable extends BitmapDrawable { private final WeakReference<BitmapWorkerTask> bitmapWorkerTaskReference; public AsyncDrawable(Resources res, Bitmap bitmap, BitmapWorkerTask bitmapWorkerTask) { super(res, bitmap); bitmapWorkerTaskReference = new WeakReference<BitmapWorkerTask>(bitmapWorkerTask); } public BitmapWorkerTask getBitmapWorkerTask() { return bitmapWorkerTaskReference.get(); } } /** * Called when the processing is complete and the final bitmap should be set * on the ImageView. * * @param imageView * @param bitmap */ private void setImageBitmap(ImageView imageView, Bitmap bitmap) { if (mFadeInBitmap) { // Use TransitionDrawable to fade in final TransitionDrawable td = new TransitionDrawable(new Drawable[] { new ColorDrawable(android.R.color.transparent), new BitmapDrawable(mResources, bitmap) }); // noinspection deprecation imageView.setImageDrawable(td); td.startTransition(FADE_IN_TIME); } else { imageView.setImageBitmap(bitmap); } } /** * Pause any ongoing background work. This can be used as a temporary * measure to improve performance. For example background work could be * paused when a ListView or GridView is being scrolled using a * {@link android.widget.AbsListView.OnScrollListener} to keep scrolling * smooth. * <p> * If work is paused, be sure setPauseWork(false) is called again before * your fragment or activity is destroyed (for example during * {@link android.app.Activity#onPause()}), or there is a risk the * background thread will never finish. */ public void setPauseWork(boolean pauseWork) { synchronized (mPauseWorkLock) { mPauseWork = pauseWork; if (!mPauseWork) { mPauseWorkLock.notifyAll(); } } } protected class CacheAsyncTask extends AsyncTask<Object, Void, Void> { @Override protected Void doInBackground(Object... params) { switch ((Integer) params[0]) { case MESSAGE_CLEAR: clearCacheInternal(); break; case MESSAGE_INIT_DISK_CACHE: initDiskCacheInternal(); break; case MESSAGE_FLUSH: flushCacheInternal(); break; case MESSAGE_CLOSE: closeCacheInternal(); break; } return null; } } protected void initDiskCacheInternal() { if (mImageCache != null) { mImageCache.initDiskCache(); } } protected void clearCacheInternal() { if (mImageCache != null) { mImageCache.clearCache(); } } protected void flushCacheInternal() { if (mImageCache != null) { mImageCache.flush(); } } protected void closeCacheInternal() { if (mImageCache != null) { mImageCache.close(); mImageCache = null; } } public void clearCache() { new CacheAsyncTask().execute(MESSAGE_CLEAR); } public void flushCache() { new CacheAsyncTask().execute(MESSAGE_FLUSH); } public void closeCache() { new CacheAsyncTask().execute(MESSAGE_CLOSE); } }