Java tutorial
/* * Copyright (C) 2013 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.itsherpa.andg.imageloader; import glas.bbsystem.BuildConfig; import java.io.FileDescriptor; 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.os.Build; import android.support.v4.app.FragmentManager; import android.widget.ImageView; import com.itsherpa.andg.util.LogUtils; /** * 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 ContactImageLoader { private static final String TAG = "ImageLoader"; private static final int FADE_IN_TIME = 200; private ContactImageCache mImageCache; private Bitmap mLoadingBitmap; private boolean mFadeInBitmap = true; private boolean mPauseWork = false; private final Object mPauseWorkLock = new Object(); private int mImageSize; private Resources mResources; protected ContactImageLoader(Context context, int imageSize) { mResources = context.getResources(); mImageSize = imageSize; } public int getImageSize() { return mImageSize; } /** * Load an image specified by the data parameter into an ImageView (override * {@link ContactImageLoader#processBitmap(Object)} to define the processing * logic). 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) { imageView.setImageBitmap(mLoadingBitmap); return; } Bitmap bitmap = null; if (mImageCache != null) { bitmap = mImageCache.getBitmapFromMemCache(String.valueOf(data)); } if (bitmap != null) { // Bitmap found in memory cache imageView.setImageBitmap(bitmap); } 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); } } /** * Set placeholder bitmap that shows when the the background thread is * running. * * @param resId * Resource ID of loading image. */ public void setLoadingImage(int resId) { mLoadingBitmap = BitmapFactory.decodeResource(mResources, resId); } /** * Adds an {@link ContactImageCache} to this image loader. * * @param fragmentManager * A FragmentManager to use to retain the cache over * configuration changes such as an orientation change. * @param memCacheSizePercent * The cache size as a percent of available app memory. */ public void addImageCache(FragmentManager fragmentManager, float memCacheSizePercent) { mImageCache = ContactImageCache.getInstance(fragmentManager, memCacheSizePercent); } /** * 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; } /** * 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 ContactImageLoader#loadImage(Object, ImageView)} * @return The processed bitmap */ protected abstract Bitmap processBitmap(Object data); /** * Cancels any pending work attached to the provided 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.data; LogUtils.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 (BuildConfig.DEBUG) { LogUtils.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, Bitmap> { private Object data; private final WeakReference<ImageView> imageViewReference; public BitmapWorkerTask(ImageView imageView) { imageViewReference = new WeakReference<ImageView>(imageView); } /** * Background processing. */ @Override protected Bitmap doInBackground(Object... params) { if (BuildConfig.DEBUG) { LogUtils.d(TAG, "doInBackground - starting work"); } data = params[0]; final String dataString = String.valueOf(data); Bitmap bitmap = 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 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 (!isCancelled() && getAttachedImageView() != null) { bitmap = processBitmap(params[0]); } // 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 && mImageCache != null) { mImageCache.addBitmapToCache(dataString, bitmap); } if (BuildConfig.DEBUG) { LogUtils.d(TAG, "doInBackground - finished work"); } return bitmap; } /** * Once the image is processed, associates it to the imageView */ @Override protected void onPostExecute(Bitmap bitmap) { // if cancel was called on this task or the "exit early" flag is set // then we're done if (isCancelled()) { bitmap = null; } final ImageView imageView = getAttachedImageView(); if (bitmap != null && imageView != null) { if (BuildConfig.DEBUG) { LogUtils.d(TAG, "onPostExecute - setting bitmap"); } setImageBitmap(imageView, bitmap); } } @TargetApi(Build.VERSION_CODES.HONEYCOMB) @Override protected void onCancelled(Bitmap bitmap) { if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) { super.onCancelled(bitmap); } else { 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(); } } /** * Called when the processing is complete and the final bitmap should be set * on the ImageView. * * @param imageView * The ImageView to set the bitmap to. * @param bitmap * The new bitmap to set. */ @TargetApi(Build.VERSION_CODES.JELLY_BEAN) @SuppressWarnings("deprecation") private void setImageBitmap(ImageView imageView, Bitmap bitmap) { if (mFadeInBitmap) { // Transition drawable to fade from loading bitmap to final bitmap final TransitionDrawable td = new TransitionDrawable(new Drawable[] { new ColorDrawable(android.R.color.transparent), new BitmapDrawable(mResources, bitmap) }); if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) { imageView.setBackground(imageView.getDrawable()); } else { imageView.setBackgroundDrawable(imageView.getDrawable()); } imageView.setImageDrawable(td); td.startTransition(FADE_IN_TIME); } else { imageView.setImageBitmap(bitmap); } } /** * 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(); } } } /** * Decode and sample down a bitmap from a file input stream to the requested * width and height. * * @param fileDescriptor * The file descriptor to read from * @param reqWidth * The requested width of the resulting bitmap * @param reqHeight * The requested height of the resulting bitmap * @return A bitmap sampled down from the original with the same aspect * ratio and dimensions that are equal to or greater than the * requested width and height */ public static Bitmap decodeSampledBitmapFromDescriptor(FileDescriptor fileDescriptor, int reqWidth, int reqHeight) { // First decode with inJustDecodeBounds=true to check dimensions final BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = true; BitmapFactory.decodeFileDescriptor(fileDescriptor, null, options); // Calculate inSampleSize options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight); // Decode bitmap with inSampleSize set options.inJustDecodeBounds = false; return BitmapFactory.decodeFileDescriptor(fileDescriptor, null, options); } /** * Calculate an inSampleSize for use in a {@link BitmapFactory.Options} * object when decoding bitmaps using the decode* methods from * {@link BitmapFactory}. This implementation calculates the closest * inSampleSize that will result in the final decoded bitmap having a width * and height equal to or larger than the requested width and height. This * implementation does not ensure a power of 2 is returned for inSampleSize * which can be faster when decoding but results in a larger bitmap which * isn't as useful for caching purposes. * * @param options * An options object with out* params already populated (run * through a decode* method with inJustDecodeBounds==true * @param reqWidth * The requested width of the resulting bitmap * @param reqHeight * The requested height of the resulting bitmap * @return The value to be used for inSampleSize */ public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) { // Raw height and width of image final int height = options.outHeight; final int width = options.outWidth; int inSampleSize = 1; if (height > reqHeight || width > reqWidth) { // Calculate ratios of height and width to requested height and // width final int heightRatio = Math.round((float) height / (float) reqHeight); final int widthRatio = Math.round((float) width / (float) reqWidth); // Choose the smallest ratio as inSampleSize value, this will // guarantee a final image // with both dimensions larger than or equal to the requested height // and width. inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio; // This offers some additional logic in case the image has a strange // aspect ratio. For example, a panorama may have a much larger // width than height. In these cases the total pixels might still // end up being too large to fit comfortably in memory, so we should // be more aggressive with sample down the image (=larger // inSampleSize). final float totalPixels = width * height; // Anything more than 2x the requested pixels we'll sample down // further final float totalReqPixelsCap = reqWidth * reqHeight * 2; while (totalPixels / (inSampleSize * inSampleSize) > totalReqPixelsCap) { inSampleSize++; } } return inSampleSize; } }