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.androidpi.bricks.gallery.lru.cache; 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.util.Log; import android.widget.ImageView; import android.widget.Toast; import com.androidpi.app.bricks.common.AppUtil; import com.androidpi.bricks.gallery.BuildConfig; import com.androidpi.bricks.gallery.task.AsyncExecutor; import java.lang.ref.WeakReference; /** * 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 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 final Object mPauseWorkLock = new Object(); protected boolean mPauseWork = false; protected Resources mResources; private Context mContext; private ImageCache mImageCache; private ImageCache.ImageCacheParams mImageCacheParams; private Bitmap mLoadingBitmap; private boolean mFadeInBitmap = true; private boolean mExitTasksEarly = false; protected ImageWorker(Context context) { mContext = context; mResources = context.getResources(); } /** * 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) { final Object bitmapData = bitmapWorkerTask.mData; Log.d(TAG, "cancelWork - cancelled work for " + bitmapData); } } } /** * 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) { // BEGIN_INCLUDE(cancel_potential_work) final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView); if (bitmapWorkerTask != null) { final Object bitmapData = bitmapWorkerTask.mData; 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; // END_INCLUDE(cancel_potential_work) } /** * @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; } /** * 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(android.support.v4.app.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) { if (data == null) { return; } BitmapDrawable value = null; if (mImageCache != null) { value = mImageCache.getBitmapFromMemCache(String.valueOf(data)); } if (value != null) { // Bitmap found in memory cache imageView.setImageDrawable(value); } else if (cancelPotentialWork(data, imageView)) { // BEGIN_INCLUDE(execute_background_task) final BitmapWorkerTask task = new BitmapWorkerTask(data, 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(AsyncExecutor.instance().THREAD_POOL_EXECUTOR); // END_INCLUDE(execute_background_task) } } /** * 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(FragmentManager fragmentManager, ImageCache.ImageCacheParams cacheParams) { mImageCacheParams = cacheParams; mImageCache = ImageCache.getInstance(fragmentManager, mImageCacheParams); new CacheAsyncTask().execute(MESSAGE_INIT_DISK_CACHE); } /** * Adds an {@link ImageCache} to this {@link ImageWorker} to handle disk and memory bitmap * caching. * * @param activity * @param diskCacheDirectoryName See {@link * ImageCache.ImageCacheParams#ImageCacheParams(android.content.Context, String)} . */ public void addImageCache(FragmentActivity activity, String diskCacheDirectoryName) { mImageCacheParams = new ImageCache.ImageCacheParams(activity, diskCacheDirectoryName); mImageCache = ImageCache.getInstance(activity.getSupportFragmentManager(), 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, android.widget.ImageView)} * @return The processed bitmap */ protected abstract Bitmap processBitmap(Object data); /** @return The {@link ImageCache} object currently being used by this ImageWorker. */ protected ImageCache getImageCache() { return mImageCache; } /** * 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(imageView.getResources().getColor(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 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); } /** * 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(); } } /** The actual AsyncTask that will asynchronously process the image. */ private class BitmapWorkerTask extends AsyncTask<Void, Void, BitmapDrawable> { private final WeakReference<ImageView> imageViewReference; private Object mData; public BitmapWorkerTask(Object data, ImageView imageView) { mData = data; imageViewReference = new WeakReference<ImageView>(imageView); } /** Background processing. */ @Override protected BitmapDrawable doInBackground(Void... params) { // BEGIN_INCLUDE(load_bitmap_in_background) if (BuildConfig.DEBUG) { Log.d(TAG, "doInBackground - starting work"); } final String dataString = String.valueOf(mData); 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); } // 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(mData); } // 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 (AppUtil.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); } } if (BuildConfig.DEBUG) { Log.d(TAG, "doInBackground - finished work"); } return drawable; // END_INCLUDE(load_bitmap_in_background) } /** Once the image is processed, associates it to the imageView */ @Override protected void onPostExecute(BitmapDrawable value) { // BEGIN_INCLUDE(complete_background_work) // 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); } // END_INCLUDE(complete_background_work) } @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; } } protected class CacheAsyncTask extends AsyncTask<Object, Void, Object> { @Override protected Object doInBackground(Object... params) { int message = (Integer) params[0]; switch (message) { case MESSAGE_CLEAR: clearCacheInternal(); break; case MESSAGE_INIT_DISK_CACHE: initDiskCacheInternal(); break; case MESSAGE_FLUSH: flushCacheInternal(); break; case MESSAGE_CLOSE: closeCacheInternal(); break; } return message; } @Override protected void onPostExecute(Object result) { int message = (Integer) result; switch (message) { case MESSAGE_CLEAR: Toast.makeText(mContext, "Cache cleared.", Toast.LENGTH_SHORT).show(); break; } } } }