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.cloudsynch.quickshare.utils.thumbnail; import java.lang.ref.WeakReference; import android.content.Context; import android.content.res.Resources; import android.graphics.Bitmap; 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.FragmentActivity; import android.support.v4.app.FragmentManager; import android.util.Log; import android.widget.AbsListView; import android.widget.ImageView; import com.cloudsynch.quickshare.utils.LogUtil; /** * 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 class ImageWorker { private static final String TAG = "ImageWorker"; private static final int FADE_IN_TIME = 200; private Context mContext; private ImageCache mImageCache; private ImageCache.ImageCacheParams mImageCacheParams; private boolean mFadeInBitmap = false; 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; private AbsListView.OnScrollListener mScrollerListener = new AbsListView.OnScrollListener() { @Override public void onScrollStateChanged(AbsListView absListView, int scrollState) { // Pause fetcher to ensure smoother scrolling when flinging if (scrollState == AbsListView.OnScrollListener.SCROLL_STATE_FLING) { ImageWorker.this.setPauseWork(true); } else { ImageWorker.this.setPauseWork(false); } } @Override public void onScroll(AbsListView absListView, int firstVisibleItem, int visibleItemCount, int totalItemCount) { } }; public AbsListView.OnScrollListener getScrollerListener() { return mScrollerListener; } public ImageWorker(Context context) { mContext = context; mResources = context.getResources(); } /** * Load an image specified by the data parameter into an ImageView * (implement {@link LoadMethod#} 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, Bitmap loading, LoadMethod method) { 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)) { final BitmapWorkerTask task = new BitmapWorkerTask(imageView); final AsyncDrawable asyncDrawable = new AsyncDrawable(mResources, loading, 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, method); } } /** * 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); } /** * @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. * * @param imageView */ public static void cancelWork(ImageView imageView) { final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView); if (bitmapWorkerTask != null) { bitmapWorkerTask.cancel(true); if (LogUtil.DEBUG) { final Object bitmapData = bitmapWorkerTask.data; 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) { final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView); if (bitmapWorkerTask != null) { final Object bitmapData = bitmapWorkerTask.data; if (bitmapData == null || !bitmapData.equals(data)) { bitmapWorkerTask.cancel(true); if (LogUtil.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) { if (LogUtil.DEBUG) { Log.d(TAG, "doInBackground - starting work"); } data = params[0]; final String dataString = String.valueOf(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); } // 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 = ((LoadMethod) params[1]).processBitmap(params[0], mContext); } // 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); } } if (LogUtil.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 (LogUtil.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 }); 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_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); } public static interface LoadMethod { public Bitmap processBitmap(Object obj, Context context); } }