Added asynchronous loading of template thumbnail

Author: opticod

source-code/app/src/main/java/org/buildmlearn/toolkit/adapter/TemplateAdapter.java

@@ -2,7 +2,13 @@
 
 import android.app.Activity;
 import android.content.Context;
+import android.content.res.Resources;
+import android.graphics.Bitmap;
+import android.graphics.BitmapFactory;
 import android.graphics.Color;
+import android.graphics.drawable.BitmapDrawable;
+import android.graphics.drawable.Drawable;
+import android.os.AsyncTask;
 import android.support.annotation.ColorRes;
 import android.support.v7.widget.CardView;
 import android.support.v7.widget.RecyclerView;
@@ -15,6 +21,8 @@
 import org.buildmlearn.toolkit.R;
 import org.buildmlearn.toolkit.model.Template;
 
+import java.lang.ref.WeakReference;
+
 /**
  * @brief Adapter used for showing Templates available in the toolkit
  * <p>
@@ -32,6 +40,35 @@ public TemplateAdapter(Context context) {
         this.context = context;
     }
 
+    public static boolean cancelPotentialWork(int data, ImageView imageView) {
+        final BitmapWorkerTask bitmapWorkerTask = getBitmapWorkerTask(imageView);
+
+        if (bitmapWorkerTask != null) {
+            final int bitmapData = bitmapWorkerTask.data;
+            // If bitmapData is not yet set or it differs from the new data
+            if (bitmapData == 0 || bitmapData != data) {
+                // Cancel previous task
+                bitmapWorkerTask.cancel(true);
+            } else {
+                // The same work is already in progress
+                return false;
+            }
+        }
+        // No task associated with the ImageView, or an existing task was cancelled
+        return true;
+    }
+
+    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;
+    }
+
     public void setOnClickListener(ViewHolder.SetOnClickListener clickListener) {
         this.listener = clickListener;
     }
@@ -67,12 +104,18 @@ public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
 
         vh.getTitle().setText(template.getTitle());
         vh.getDescription().setText(template.getDescription());
-        vh.getImage().setImageResource(template.getImage());
 
         int color = colors[position % colors.length].getColor();
         vh.getCardView().setCardBackgroundColor(color);
         vh.setItemClickListener(listener);
 
+        if (cancelPotentialWork(template.getImage(), vh.getImage())) {
+            final BitmapWorkerTask task = new BitmapWorkerTask(context, vh.getImage());
+            final AsyncDrawable asyncDrawable =
+                    new AsyncDrawable(context.getResources(), null, task);
+            vh.getImage().setImageDrawable(asyncDrawable);
+            task.execute(template.getImage());
+        }
     }
 
     @Override
@@ -170,4 +213,94 @@ public interface SetOnClickListener {
             void onItemClick(int position);
         }
     }
+
+    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();
+        }
+    }
+
+    class BitmapWorkerTask extends AsyncTask<Integer, Void, Bitmap> {
+        private final WeakReference<ImageView> imageViewReference;
+        private int data = 0;
+        private Context mContext;
+
+        public BitmapWorkerTask(Context context, ImageView imageView) {
+            // Use a WeakReference to ensure the ImageView can be garbage collected
+            mContext = context;
+            imageViewReference = new WeakReference<ImageView>(imageView);
+        }
+
+        // Decode image in background.
+        @Override
+        protected Bitmap doInBackground(Integer... params) {
+            data = params[0];
+            return decodeSampledBitmapFromResource(context.getResources(), data, 141, 180);
+        }
+
+        // Once complete, see if ImageView is still around and set bitmap.
+        @Override
+        protected void onPostExecute(Bitmap bitmap) {
+            if (isCancelled()) {
+                bitmap = null;
+            }
+
+            if (imageViewReference != null && bitmap != null) {
+                final ImageView imageView = imageViewReference.get();
+                final BitmapWorkerTask bitmapWorkerTask =
+                        getBitmapWorkerTask(imageView);
+                if (this == bitmapWorkerTask && imageView != null) {
+                    imageView.setImageBitmap(bitmap);
+                }
+            }
+        }
+
+        public Bitmap decodeSampledBitmapFromResource(Resources res, int resId,
+                                                      int reqWidth, int reqHeight) {
+
+            // First decode with inJustDecodeBounds=true to check dimensions
+            final BitmapFactory.Options options = new BitmapFactory.Options();
+            options.inJustDecodeBounds = true;
+            BitmapFactory.decodeResource(res, resId, options);
+
+            // Calculate inSampleSize
+            options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
+
+            // Decode bitmap with inSampleSize set
+            options.inJustDecodeBounds = false;
+            return BitmapFactory.decodeResource(res, resId, options);
+        }
+
+        public 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) {
+
+                final int halfHeight = height / 2;
+                final int halfWidth = width / 2;
+
+                // Calculate the largest inSampleSize value that is a power of 2 and keeps both
+                // height and width larger than the requested height and width.
+                while ((halfHeight / inSampleSize) >= reqHeight
+                        && (halfWidth / inSampleSize) >= reqWidth) {
+                    inSampleSize *= 2;
+                }
+            }
+
+            return inSampleSize;
+        }
+    }
 }