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 gr.unfold.android.tsibato.images; import gr.unfold.android.tsibato.AppConfig; import gr.unfold.android.tsibato.drawable.RecyclingBitmapDrawable; import gr.unfold.android.tsibato.util.Utils; import java.lang.ref.WeakReference; import android.annotation.TargetApi; 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.FragmentManager; import android.util.Log; import android.widget.ImageView; /** * 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 ImageCache mImageCache; private ImageCache.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 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; protected ImageWorker(Context context) { mResources = context.getResources(); } /** * Load an image specified by the data parameter into an ImageView using a memory and * disk cache. 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. */ public void loadImage(Object data, ImageView imageView) { if (data == null) { return; } BitmapDrawable value = null; if (mImageCache != null) { value = mImageCache.getBitmapFromMemCache(String.valueOf(data)); } if (value != null) { imageView.setImageDrawable(value); } else if (cancelPotentialWork(data, imageView)) { final BitmapWorkerTask task = new BitmapWorkerTask(imageView); final AsyncDrawable asyncDrawable = new AsyncDrawable(mResources, mLoadingBitmap, task); imageView.setImageDrawable(asyncDrawable); task.execute(data); } } public void setLoadingImage(int resId) { mLoadingBitmap = BitmapFactory.decodeResource(mResources, resId); } public void addImageCache(FragmentManager fragmentManager, ImageCache.ImageCacheParams cacheParams) { mImageCacheParams = cacheParams; mImageCache = ImageCache.getInstance(fragmentManager, mImageCacheParams); new CacheAsyncTask().execute(MESSAGE_INIT_DISK_CACHE); } public void setExitTasksEarly(boolean exitTasksEarly) { mExitTasksEarly = exitTasksEarly; setPauseWork(false); } /** Main method for subclasses to override to define any processing that must happen to produce * the final bitmap. This will be executed in a background thread and be long running. */ protected abstract Bitmap processBitmap(Object data); protected ImageCache getImageCache() { return mImageCache; } /** Returns true if the current work has been cancelled or if there is no work in progress, * false if the work in progress deals with the same data. */ 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 (AppConfig.DEBUG) { Log.d(TAG, "cancelPotentialWork - cancelled work for " + data); } } else { // The same work is already in progress. return false; } } return true; } /** Retrieve the currently active work task (if any) associated with this imageView, or 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); } @Override protected BitmapDrawable doInBackground(Object... params) { if (AppConfig.DEBUG) { Log.d(TAG, "doInBackground - starting work"); } data = params[0]; final String dataString = String.valueOf(data); Bitmap bitmap = null; BitmapDrawable drawable = null; synchronized (mPauseWorkLock) { while (mPauseWork && !isCancelled()) { try { mPauseWorkLock.wait(); } catch (InterruptedException e) { } } } // If the image cache is available and task has not been cancelled and the ImageView is still // bound back to this task and our "exit early" flag is not set then fetch the bitmap from the disk cache if (mImageCache != null && !isCancelled() && getAttachedImageView() != null && !mExitTasksEarly) { bitmap = mImageCache.getBitmapFromDiskCache(dataString); } // If the image not found in cache and task has not been cancelled and the ImageView is still // bound back to this task and our "exit early" flag is not set then fetch call the main process method if (bitmap == null && !isCancelled() && getAttachedImageView() != null && !mExitTasksEarly) { bitmap = processBitmap(params[0]); } if (bitmap != null) { if (Utils.hasHoneycomb()) { drawable = new BitmapDrawable(mResources, bitmap); } else { // Running on Gingerbread or older, so wrap in a RecyclingBitmapDrawable which will recycle automatically drawable = new RecyclingBitmapDrawable(mResources, bitmap); } if (mImageCache != null) { mImageCache.addBitmapToCache(dataString, drawable); } } if (AppConfig.DEBUG) { Log.d(TAG, "doInBackground - finished work"); } return drawable; } @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 (AppConfig.DEBUG) { Log.d(TAG, "onPostExecute - setting bitmap"); } setImageDrawable(imageView, value); } } @Override protected void onCancelled() { super.onCancelled(); synchronized (mPauseWorkLock) { mPauseWorkLock.notifyAll(); } } @Override protected void onCancelled(BitmapDrawable value) { 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(); } } @TargetApi(16) @SuppressWarnings("deprecation") 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 if (Utils.hasJellyBean()) { imageView.setBackground(new BitmapDrawable(mResources, mLoadingBitmap)); } else { imageView.setBackgroundDrawable(new BitmapDrawable(mResources, mLoadingBitmap)); } imageView.setImageDrawable(td); td.startTransition(FADE_IN_TIME); } else { imageView.setImageDrawable(drawable); } } 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); } }