Android Open Source - ImageGrabber Image Worker

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Back to project page ImageGrabber.

License

The source code is released under:

Apache License

Java Source Code

package com.herroworld.imagegrabber;
//from w  w  w .ja v a2s .  c o m
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.util.Log;
import android.widget.ImageView;

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. It also allows forcing a network response to refresh the disk cache.
 */
public abstract class ImageWorker {
    private static final String TAG = ImageWorker.class.getSimpleName();

    private ImageCache mImageCache;
    private Bitmap mLoadingBitmap;
    private boolean mFadeInBitmap = true;
    private boolean mExitTasksEarly = false;
    /* Force network response */
    private boolean mAlwaysFetchFromServer = false;
    private int mFadeInTime = 200;

    protected Context mContext;

    protected ImageWorker(Context context) {
        mContext = context;
    }

    /**
     * Set the fade in time when bitmap is loaded into the image view.
     * 
     * @param fadeInTime Fade in time in milliseconds
     */
    public void setFadeInTime(int fadeInTime) {
        mFadeInTime = fadeInTime;
    }

    /**
     * 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 set using {@link ImageWorker#setImageCache(ImageCache)}. 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 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<BitmapWorkerTask> asyncDrawable =
                    new AsyncDrawable<BitmapWorkerTask>(mContext.getResources(), mLoadingBitmap,
                            task);
            imageView.setImageDrawable(asyncDrawable);
            task.execute(data);
        }
    }

    /**
     * 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(mContext.getResources(), resId);
    }

    /**
     * Set the {@link ImageCache} object to use with this ImageWorker.
     * 
     * @param cacheCallback
     */
    public void setImageCache(ImageCache cacheCallback) {
        mImageCache = cacheCallback;
    }

    /**
     * Get the {@link ImageCache} object for reuse.
     * 
     * @return The {@link ImageCache} object
     */
    public ImageCache getImageCache() {
        return mImageCache;
    }

    /**
     * If set to true, the image will fade-in once it has been loaded by the
     * background thread.
     * 
     * @param fadeIn
     */
    public void setImageFadeIn(boolean fadeIn) {
        mFadeInBitmap = fadeIn;
    }

    /**
     * If set to true, image will be returned from cache if available and
     * simultaneously re-fetch the image from network if it has changed since
     * the last time.
     * 
     * @param fetch
     */
    public void setAlwaysFetchFromServer(boolean fetch) {
        mAlwaysFetchFromServer = fetch;
    }

    /**
     * If set to true, all intermediate tasks will be cancelled.
     * 
     * @param exitTasksEarly
     */
    public void setExitTasksEarly(boolean exitTasksEarly) {
        mExitTasksEarly = exitTasksEarly;
    }

    /**
     * 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, ImageView)}
     * @param forceFetch Whether or not to force a network response even if the
     *            image is cached
     * @return The processed bitmap
     */
    protected abstract Bitmap processBitmap(Object data, boolean forceFetch);

    public static void cancelWork(ImageView imageView) {
        final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView);
        if (bitmapWorkerTask != null) {
            bitmapWorkerTask.cancel(true);
            if (Utils.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.
     */
    private 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 (Utils.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<BitmapWorkerTask> asyncDrawable = (AsyncDrawable) drawable;
                return asyncDrawable.getBitmapWorkerTask();
            }
        }
        return null;
    }

    /**
     * @param imageView Any imageView
     * @return Retrieve the currently active re-fetch work task (if any)
     *         associated with this imageView. null if there is no such task.
     */
    private static BitmapRefetchWorkerTask getBitmapRefetchWorkerTask(ImageView imageView) {
        if (imageView != null) {
            final Drawable drawable = imageView.getDrawable();
            if (drawable instanceof AsyncDrawable) {
                final AsyncDrawable<BitmapRefetchWorkerTask> 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) {
            data = params[0];
            final String dataString = String.valueOf(data);
            Bitmap bitmap = null;

            // 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(params[0], false);
            }

            // 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);
            }

            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() || mExitTasksEarly) {
                bitmap = null;
            }

            final ImageView imageView = getAttachedImageView();
            if (bitmap != null && imageView != null) {
                setImageBitmap(imageView, bitmap);

                // if the user chooses to force a network response every time
                // the disk cache is accessed
                if (mAlwaysFetchFromServer) {
                    if (imageView != null) {
                        final BitmapRefetchWorkerTask task = new BitmapRefetchWorkerTask(imageView);
                        task.execute(data);
                    }
                }
            }
        }

        /**
         * 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;
        }
    }

    /**
     * The actual AsyncTask that will asynchronously process the re-fetched
     * image.
     */
    private class BitmapRefetchWorkerTask extends AsyncTask<Object, ImageView, Bitmap> {
        private Object data;
        private final WeakReference<ImageView> imageViewReference;

        public BitmapRefetchWorkerTask(ImageView imageView) {
            imageViewReference = new WeakReference<ImageView>(imageView);
            publishProgress(imageView);
        }

        /**
         * Need to update the ImageView with a AsyncDrawable immediately to
         * prevent a race condition.
         */
        @Override
        protected void onProgressUpdate(ImageView... params) {
            final AsyncDrawable<BitmapRefetchWorkerTask> asyncDrawable =
                    new AsyncDrawable<BitmapRefetchWorkerTask>(mContext.getResources(),
                            mLoadingBitmap, this);
            ImageView imageView = params[0];
            imageView.setImageDrawable(asyncDrawable);
        }

        @Override
        protected void onPreExecute() {
            ImageView imageView = imageViewReference.get();
            if (imageView != null) {
                final AsyncDrawable<BitmapRefetchWorkerTask> asyncDrawable =
                        new AsyncDrawable<BitmapRefetchWorkerTask>(mContext.getResources(),
                                mLoadingBitmap, this);
                imageView.setImageDrawable(asyncDrawable);
            }
        }

        /**
         * Background processing.
         */
        @Override
        protected Bitmap doInBackground(Object... params) {
            data = params[0];
            final String dataString = String.valueOf(data);
            Bitmap bitmap = processBitmap(params[0], true);

            if (bitmap != null && mImageCache != null) {
                mImageCache.addBitmapToCache(dataString, bitmap);
            }

            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() || mExitTasksEarly) {
                bitmap = null;
            }

            final ImageView imageView = getAttachedImageView();
            if (bitmap != null && imageView != null) {
                setImageBitmap(imageView, bitmap);
            }
        }

        /**
         * 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 BitmapRefetchWorkerTask bitmapRefetchWorkerTask = getBitmapRefetchWorkerTask(imageView);

            if (this == bitmapRefetchWorkerTask) {
                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<T> extends BitmapDrawable {
        private final WeakReference<T> bitmapWorkerTaskReference;

        public AsyncDrawable(Resources res, Bitmap bitmap, T bitmapWorkerTask) {
            super(res, bitmap);

            bitmapWorkerTaskReference =
                    new WeakReference<T>(bitmapWorkerTask);
        }

        public T getBitmapWorkerTask() {
            return bitmapWorkerTaskReference.get();
        }
    }

    /**
     * Called when the processing is complete and the final bitmap should be set
     * on the ImageView.
     * 
     * @param imageView
     * @param bitmap
     */
    private void setImageBitmap(ImageView imageView, Bitmap bitmap) {
        if (mFadeInBitmap) {
            // Transition drawable with a transparent drwabale and the final
            // bitmap
            final TransitionDrawable td =
                    new TransitionDrawable(new Drawable[] {
                            new ColorDrawable(android.R.color.transparent),
                            new BitmapDrawable(mContext.getResources(), bitmap)
                    });
            // Set background to loading bitmap
            imageView.setBackgroundDrawable(
                    new BitmapDrawable(mContext.getResources(), mLoadingBitmap));

            imageView.setImageDrawable(td);
            td.startTransition(mFadeInTime);
        } else {
            imageView.setImageBitmap(bitmap);
        }
    }
}

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