Java tutorial
/* * Copyright (C) 2012 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. */ package com.rsegismont.androlife.common.utils; import java.lang.ref.WeakReference; import java.util.ArrayList; import java.util.List; import android.content.Context; import android.content.res.Resources; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Point; import android.graphics.drawable.BitmapDrawable; import android.graphics.drawable.ColorDrawable; import android.graphics.drawable.Drawable; import android.graphics.drawable.TransitionDrawable; import android.support.v4.app.FragmentManager; import android.util.Log; import android.widget.ImageView; import com.rsegismont.androlife.BuildConfig; /** * 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"; private static final int FADE_IN_TIME = 200; private ImageCacher mImageCache; private ImageCacher.ImageCacheParams mImageCacheParams; private Bitmap mLoadingBitmap; private boolean mFadeInBitmap = true; private boolean mExitTasksEarly = false; protected boolean mPauseWork = false; private final Object mPauseWorkLock = new Object(); protected Resources mResources; private static List<String> badUrls = new ArrayList<String>(); 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 int MESSAGE_CLEAR_MEMORY = 4; private static final int DEFAULT_WIDTH = 512; private static final int DEFAULT_HEIGHT = 288; protected ImageWorker(Context context) { mResources = context.getResources(); badUrls = new ArrayList<String>(); } protected void addToBadUrls(String urlString, int reqWidth, int reqHeight) { badUrls.add(urlString + reqWidth + reqHeight); } public void loadImage(Object data, ImageView imageView) { loadImage(data, imageView, DEFAULT_WIDTH, DEFAULT_HEIGHT); } /** * 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 added using * {@link ImageWorker#addImageCache(FragmentManager, ImageCache.ImageCacheParams)}. 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, int reqWdith, int reqHeight) { final boolean workCancelled = cancelPotentialWork(data, imageView); if (badUrls.contains("" + data + reqWdith + reqHeight) || (data == null)) { imageView.setImageBitmap(null); imageView.setImageBitmap(mLoadingBitmap); return; } BitmapDrawable value = null; if (mImageCache != null) { value = mImageCache.getBitmapFromMemCache(String.valueOf(data), reqWdith, reqHeight); } if (value != null) { // Bitmap found in memory cache imageView.setImageBitmap(null); imageView.setImageDrawable(value); } else if (workCancelled) { final BitmapWorkerTask task = new BitmapWorkerTask(imageView); final AsyncDrawable asyncDrawable = new AsyncDrawable(mResources, mLoadingBitmap, task); imageView.setImageDrawable(asyncDrawable); // NOTE: This uses a custom version of AsyncTask that has been pulled from the // framework and slightly modified. Refer to the docs at the top of the class // for more info on what was changed. task.executeOnExecutor(AsyncTask.DUAL_THREAD_EXECUTOR, data, reqWdith, reqHeight); } } /** * 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 {@link ImageWorker} to handle disk and memory bitmap caching. * * @param fragmentManager * @param cacheParams * The cache parameters to use for the image cache. */ public void addImageCache(ImageCacher.ImageCacheParams cacheParams) { mImageCacheParams = cacheParams; mImageCache = new ImageCacher(mImageCacheParams); 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; } 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, int reqWidth, int reqHeight, Point originalValues); /** * @return The {@link ImageCache} object currently being used by this ImageWorker. */ public ImageCacher getImageCache() { return mImageCache; } /** * 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); if (BuildConfig.DEBUG) { Log.d(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, BitmapDrawable> { private Object data; private final WeakReference<ImageView> imageViewReference; public BitmapWorkerTask(ImageView imageView) { imageViewReference = new WeakReference<ImageView>(imageView); } /** * Background processing. */ @Override protected BitmapDrawable doInBackground(Object... params) { Point point = new Point(); data = params[0]; final String dataString = String.valueOf(data); if (BuildConfig.DEBUG) { Log.d(TAG, "doInBackground - starting work " + data); } Bitmap bitmap = null; BitmapDrawable drawable = 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, Integer.valueOf("" + params[1]), Integer.valueOf("" + params[2]), point); } // 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], Integer.valueOf("" + params[1]), Integer.valueOf("" + params[2]), point); } // 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) { if (Utils.hasHoneycomb()) { // Running on Honeycomb or newer, so wrap in a standard BitmapDrawable drawable = new BitmapDrawable(mResources, bitmap); } else { // Running on Gingerbread or older, so wrap in a RecyclingBitmapDrawable // which will recycle automagically drawable = new RecyclingBitmapDrawable(mResources, bitmap); } if (mImageCache != null) { mImageCache.addBitmapToCache(dataString, drawable, Integer.valueOf("" + params[1]), Integer.valueOf("" + params[2]), point); } } if (BuildConfig.DEBUG) { Log.d(TAG, "doInBackground - finished work"); } return drawable; } /** * Once the image is processed, associates it to the imageView */ @Override protected void onPostExecute(BitmapDrawable value) { // if cancel was called on this task or the "exit early" flag is set then we're done if (isCancelled() || mExitTasksEarly) { value = null; } final ImageView imageView = getAttachedImageView(); if (value != null && imageView != null) { if (BuildConfig.DEBUG) { Log.d(TAG, "onPostExecute - setting bitmap"); } setImageDrawable(imageView, value); } } @Override protected void onCancelled(BitmapDrawable value) { super.onCancelled(value); 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 drawable should be set on the ImageView. * * @param imageView * @param drawable */ private void setImageDrawable(ImageView imageView, Drawable drawable) { if (mFadeInBitmap) { // Transition drawable with a transparent drawable and the final drawable final TransitionDrawable td = new TransitionDrawable( new Drawable[] { new ColorDrawable(android.R.color.transparent), drawable }); // Set background to loading bitmap // imageView.setBackgroundDrawable(new BitmapDrawable(mResources, mLoadingBitmap)); imageView.setImageDrawable(td); td.startTransition(FADE_IN_TIME); } else { imageView.setImageDrawable(drawable); } } /** * 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_CLEAR_MEMORY: clearMemoryInternal(); 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 clearMemoryInternal() { if (mImageCache != null) { mImageCache.clearMemoryCache(); } } protected void flushCacheInternal() { if (mImageCache != null) { mImageCache.flush(); } } protected void closeCacheInternal() { if (mImageCache != null) { mImageCache.close(); mImageCache = null; } } public void clearMemoryCache() { new CacheAsyncTask().execute(MESSAGE_CLEAR_MEMORY); } public void clearCache() { new CacheAsyncTask().execute(MESSAGE_CLEAR); } public void flushCache() { new CacheAsyncTask().execute(MESSAGE_FLUSH); } public void closeCache() { new CacheAsyncTask().execute(MESSAGE_CLOSE); } }