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.github.programmerr47.vkgroups.imageloading; 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.graphics.drawable.RoundedBitmapDrawable; import android.support.v4.graphics.drawable.RoundedBitmapDrawableFactory; import android.util.Log; import android.util.Pair; import android.widget.ImageView; import com.github.programmerr47.vkgroups.BuildConfig; 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 ImageCache mImageCache; 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 (override * {@link ImageWorker#processBitmap(Object, LoadBitmapParams)} to define the processing logic). A memory and * disk cache will be used. 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, LoadBitmapParams params) { if (data == null) { return; } handleParams(imageView, params); BitmapDrawable value = null; if (mImageCache != null) { value = mImageCache.getBitmapFromMemCache(String.valueOf(data)); } if (value != null) { // Bitmap found in memory cache Drawable finalDrawable = postProcessDrawable(value, params); imageView.setImageDrawable(finalDrawable); } 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.execute(params); //END_INCLUDE(execute_background_task) } } private void handleParams(ImageView imageView, LoadBitmapParams params) { if (params.imageHeight == 0) { params.imageHeight = imageView.getHeight(); } if (params.imageWidth == 0) { params.imageWidth = imageView.getWidth(); } } /** * Set placeholder bitmap that shows when the the background thread is running. */ public void setLoadingImage(Bitmap bitmap) { mLoadingBitmap = bitmap; } /** * Set placeholder bitmap that shows when the the background thread is running. */ public void setLoadingImage(int resId) { setLoadingImage(BitmapFactory.decodeResource(mResources, resId)); } /** * Adds an {@link ImageCache} to this {@link ImageWorker} to handle disk and memory bitmap * caching. * @param cacheParams The cache parameters to use for the image cache. */ public void addImageCache(ImageCache.ImageCacheParams cacheParams) { mImageCache = new ImageCache(cacheParams); 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. */ @SuppressWarnings("unused") public void setImageFadeIn(boolean fadeIn) { mFadeInBitmap = fadeIn; } @SuppressWarnings("unused") 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, LoadBitmapParams)} * @return The processed bitmap */ protected abstract Bitmap processBitmap(Object data, LoadBitmapParams params); /** * @return The {@link ImageCache} object currently being used by this ImageWorker. */ protected ImageCache getImageCache() { return mImageCache; } /** * Cancels any pending work attached to the provided ImageView. */ @SuppressWarnings("unused") 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; } /** * The actual AsyncTask that will asynchronously process the image. */ private class BitmapWorkerTask extends AsyncTask<LoadBitmapParams, Void, Pair<BitmapDrawable, LoadBitmapParams>> { private Object mData; private final WeakReference<ImageView> imageViewReference; public BitmapWorkerTask(Object data, ImageView imageView) { mData = data; imageViewReference = new WeakReference<>(imageView); } /** * Background processing. */ @Override protected Pair<BitmapDrawable, LoadBitmapParams> doInBackground(LoadBitmapParams... params) { //BEGIN_INCLUDE(load_bitmap_in_background) if (BuildConfig.DEBUG) { Log.d(TAG, "doInBackground - starting work"); } LoadBitmapParams loadBitmapParams = params[0]; 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 ignored) { } } } // 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, loadBitmapParams); } // 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) { drawable = new BitmapDrawable(mResources, bitmap); if (mImageCache != null) { mImageCache.addBitmapToCache(dataString, drawable); } } if (BuildConfig.DEBUG) { Log.d(TAG, "doInBackground - finished work"); } return new Pair<>(drawable, loadBitmapParams); //END_INCLUDE(load_bitmap_in_background) } /** * Once the image is processed, associates it to the imageView */ @Override protected void onPostExecute(Pair<BitmapDrawable, LoadBitmapParams> result) { //BEGIN_INCLUDE(complete_background_work) // if cancel was called on this task or the "exit early" flag is set then we're done BitmapDrawable value = result.first; LoadBitmapParams params = result.second; 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, params); } //END_INCLUDE(complete_background_work) } @Override protected void onCancelled(Pair<BitmapDrawable, LoadBitmapParams> result) { super.onCancelled(result); 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); } public BitmapWorkerTask getBitmapWorkerTask() { return bitmapWorkerTaskReference.get(); } } /** * Called when the processing is complete and the final drawable should be * set on the ImageView. */ private void setImageDrawable(ImageView imageView, BitmapDrawable drawable, LoadBitmapParams loadingParams) { Drawable finalDrawable = postProcessDrawable(drawable, loadingParams); 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)), finalDrawable }); // Set background to loading bitmap imageView.setBackgroundDrawable(new BitmapDrawable(mResources, mLoadingBitmap)); imageView.setImageDrawable(td); td.startTransition(FADE_IN_TIME); } else { imageView.setImageDrawable(finalDrawable); } } private Drawable postProcessDrawable(BitmapDrawable drawable, LoadBitmapParams loadingParams) { if (loadingParams.isRound) { Bitmap sourceBitmap = drawable.getBitmap(); RoundedBitmapDrawable roundDrawable = RoundedBitmapDrawableFactory.create(mResources, sourceBitmap); roundDrawable.setCircular(true); return roundDrawable; } else { return 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_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; } } @SuppressWarnings("unused") public void clearCache() { new CacheAsyncTask().execute(MESSAGE_CLEAR); } @SuppressWarnings("unused") public void flushCache() { new CacheAsyncTask().execute(MESSAGE_FLUSH); } @SuppressWarnings("unused") public void closeCache() { new CacheAsyncTask().execute(MESSAGE_CLOSE); } public static final class LoadBitmapParams { public int imageWidth; public int imageHeight; public boolean isRound = true; public LoadBitmapParams(int imageWidth, int imageHeight) { this.imageWidth = imageWidth; this.imageHeight = imageHeight; } public LoadBitmapParams(int imageWidth, int imageHeight, boolean isRound) { this.imageWidth = imageWidth; this.imageHeight = imageHeight; this.isRound = isRound; } } }