[NTP Snippets] 📷 Add placeholders and start caching thumbnails

chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetArticleViewHolder.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetArticleViewHolder.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetArticleViewHolder.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetArticleViewHolder.java
index d76bd1c590f129ab676224a86e9a04d31f852eb1..9a5f17921b76db17b3261c3ade976ea6457bb049 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetArticleViewHolder.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetArticleViewHolder.java
@@ -4,6 +4,14 @@
 
 package org.chromium.chrome.browser.ntp.snippets;
 
+import android.content.res.Resources;
+import android.graphics.Bitmap;
+import android.graphics.BitmapFactory;
+import android.graphics.drawable.BitmapDrawable;
+import android.graphics.drawable.Drawable;
+import android.graphics.drawable.TransitionDrawable;
+import android.media.ThumbnailUtils;
+import android.os.AsyncTask;
 import android.text.format.DateUtils;
 import android.view.LayoutInflater;
 import android.view.View;
@@ -11,6 +19,8 @@
 import android.widget.ImageView;
 import android.widget.TextView;
 
+import org.chromium.base.Log;
+import org.chromium.base.StreamUtil;
 import org.chromium.base.metrics.RecordHistogram;
 import org.chromium.base.metrics.RecordUserAction;
 import org.chromium.chrome.R;
@@ -19,15 +29,24 @@
 import org.chromium.chrome.browser.ntp.cards.NewTabPageListItem;
 import org.chromium.chrome.browser.ntp.cards.NewTabPageViewHolder;
 
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.URL;
+
 /**
  * A class that represents the view for a single card snippet.
  */
 public class SnippetArticleViewHolder extends NewTabPageViewHolder implements View.OnClickListener {
+    private static final String TAG = "NtpSnippets";
+    private static final int FADE_IN_ANIMATION_TIME_MS = 300;
+
     private final NewTabPageManager mNewTabPageManager;
-    public TextView mHeadlineTextView;
-    public TextView mPublisherTextView;
-    public TextView mArticleSnippetTextView;
-    public ImageView mThumbnailView;
+    private final TextView mHeadlineTextView;
+    private final TextView mPublisherTextView;
+    private final TextView mArticleSnippetTextView;
+    private final ImageView mThumbnailView;
+
+    private AsyncTask<String, Void, Bitmap> mThumbnailFetchingTask;
     public String mUrl;
     public int mPosition;
 
@@ -90,7 +109,72 @@ public void onBindViewHolder(NewTabPageListItem article) {
         mUrl = item.mUrl;
         mPosition = item.mPosition;
 
-        item.setThumbnailOnView(mThumbnailView);
+        updateThumbnail(item);
+    }
+
+    private void updateThumbnail(final SnippetArticle snippet) {
+        // If this view has a pending fetching task, it will display the stale thumbnail when it
+        // finishes, so we need to cancel that task.
+        if (mThumbnailFetchingTask != null) mThumbnailFetchingTask.cancel(true);
+
+        if (snippet.getThumbnailBitmap() != null) {
+            mThumbnailView.setImageBitmap(snippet.getThumbnailBitmap());
+            return;
+        }
+
+        mThumbnailView.setImageResource(R.drawable.ic_snippet_thumbnail_placeholder);
+
+        if (snippet.mThumbnailUrl.isEmpty()) {
+            Log.e(TAG, "Could not get image thumbnail due to empty URL");
+            return;
+        }
+
+        mThumbnailFetchingTask = new AsyncTask<String, Void, Bitmap>() {
+
+            @Override
+            protected Bitmap doInBackground(String... params) {
+                InputStream is = null;
+                try {
+                    is = new URL(params[0]).openStream();
+                    return BitmapFactory.decodeStream(is);
+                } catch (IOException e) {
+                    Log.e(TAG, "Could not get image thumbnail", e);
+                } finally {
+                    StreamUtil.closeQuietly(is);
+                }
+
+                return null;
+            }
+
+            @Override
+            protected void onPostExecute(Bitmap result) {
+                if (result == null) return; // Nothing to do, we keep the placeholder.
+                fadeThumbnailIn(snippet, result);
+            }
+        };
+
+        mThumbnailFetchingTask.executeOnExecutor(
+                AsyncTask.THREAD_POOL_EXECUTOR, snippet.mThumbnailUrl);
+    }
+
+    private void fadeThumbnailIn(SnippetArticle snippet, Bitmap thumbnail) {
+        // We need to crop and scale the downloaded bitmap, as the ImageView we set it on won't be
+        // able to do so when using a TransitionDrawable (as opposed to the straight bitmap).
+        // That's a limitation of TransitionDrawable, which doesn't handle layers of varying sizes.
+        Resources res = mThumbnailView.getResources();
+        int targetSize = res.getDimensionPixelSize(R.dimen.snippets_thumbnail_size);
+        Bitmap scaledThumbnail = ThumbnailUtils.extractThumbnail(
+                thumbnail, targetSize, targetSize, ThumbnailUtils.OPTIONS_RECYCLE_INPUT);
+
+        // Store the bitmap to skip the download task next time we display this snippet.
+        snippet.setThumbnailBitmap(scaledThumbnail);
+
+        // Cross-fade between the placeholder and the thumbnail.
+        Drawable[] layers = {mThumbnailView.getDrawable(),
+                new BitmapDrawable(mThumbnailView.getResources(), scaledThumbnail)};
+        TransitionDrawable transitionDrawable = new TransitionDrawable(layers);
+        mThumbnailView.setImageDrawable(transitionDrawable);
+        transitionDrawable.startTransition(FADE_IN_ANIMATION_TIME_MS);
     }
 
     @Override