Improve image loading performance by using UniversalImageLoader to background the task

Doing this required tweaking our `IconDownloader` which we give to the
UIL init method in FDroidApp. It only knew how to load from HTTP, but we
needed it to fetch `drawable://` images too (which the library
supports). In addition, it has been renamed `ImageDownloader` as it also
is now used for screenshots/feature images.

app/src/main/java/org/fdroid/fdroid/FDroidApp.java

@@ -58,7 +58,7 @@ import org.fdroid.fdroid.data.AppProvider;
 import org.fdroid.fdroid.data.InstalledAppProviderService;
 import org.fdroid.fdroid.data.Repo;
 import org.fdroid.fdroid.installer.InstallHistoryService;
-import org.fdroid.fdroid.net.IconDownloader;
+import org.fdroid.fdroid.net.ImageLoaderForUIL;
 import org.fdroid.fdroid.net.WifiStateChangeService;
 
 import java.net.URL;
@@ -280,7 +280,7 @@ public class FDroidApp extends Application {
         bluetoothAdapter = getBluetoothAdapter();
 
         ImageLoaderConfiguration config = new ImageLoaderConfiguration.Builder(getApplicationContext())
-                .imageDownloader(new IconDownloader(getApplicationContext()))
+                .imageDownloader(new ImageLoaderForUIL(getApplicationContext()))
                 .diskCache(new LimitedAgeDiskCache(
                         Utils.getIconsCacheDir(this),
                         null,

app/src/main/java/org/fdroid/fdroid/net/ImageLoaderForUIL.java

@@ -2,16 +2,20 @@ package org.fdroid.fdroid.net;
 
 import android.content.Context;
 
-import com.nostra13.universalimageloader.core.download.ImageDownloader;
+import com.nostra13.universalimageloader.core.download.BaseImageDownloader;
 
 import java.io.IOException;
 import java.io.InputStream;
 
-public class IconDownloader implements ImageDownloader {
+/**
+ * Class used by the Universal Image Loader library (UIL) to fetch images for displaying in F-Droid.
+ * See {@link org.fdroid.fdroid.FDroidApp} for where this gets configured.
+ */
+public class ImageLoaderForUIL implements com.nostra13.universalimageloader.core.download.ImageDownloader {
 
     private final Context context;
 
-    public IconDownloader(Context context) {
+    public ImageLoaderForUIL(Context context) {
         this.context = context;
     }
 
@@ -20,8 +24,13 @@ public class IconDownloader implements ImageDownloader {
         switch (Scheme.ofUri(imageUri)) {
             case ASSETS:
                 return context.getAssets().open(Scheme.ASSETS.crop(imageUri));
+
+            case DRAWABLE:
+                return new BaseImageDownloader(context).getStream(imageUri, extra);
+
             default:
                 return DownloaderFactory.create(context, imageUri).getInputStream();
         }
     }
+
 }

app/src/main/java/org/fdroid/fdroid/views/categories/CategoryController.java

@@ -4,6 +4,7 @@ import android.app.Activity;
 import android.content.Intent;
 import android.content.Context;
 import android.database.Cursor;
+import android.graphics.Bitmap;
 import android.graphics.Color;
 import android.graphics.Rect;
 import android.os.Bundle;
@@ -20,6 +21,11 @@ import android.widget.FrameLayout;
 import android.widget.ImageView;
 import android.widget.TextView;
 
+import com.nostra13.universalimageloader.core.DisplayImageOptions;
+import com.nostra13.universalimageloader.core.ImageLoader;
+import com.nostra13.universalimageloader.core.assist.ImageScaleType;
+import com.nostra13.universalimageloader.core.display.FadeInBitmapDisplayer;
+
 import org.fdroid.fdroid.R;
 import org.fdroid.fdroid.data.AppProvider;
 import org.fdroid.fdroid.data.Schema;
@@ -36,6 +42,7 @@ public class CategoryController extends RecyclerView.ViewHolder implements Loade
 
     private final Activity activity;
     private final LoaderManager loaderManager;
+    private final DisplayImageOptions displayImageOptions;
 
     private String currentCategory;
 
@@ -57,6 +64,13 @@ public class CategoryController extends RecyclerView.ViewHolder implements Loade
         RecyclerView appCards = (RecyclerView) itemView.findViewById(R.id.app_cards);
         appCards.setAdapter(appCardsAdapter);
         appCards.addItemDecoration(new ItemDecorator(activity));
+
+        displayImageOptions = new DisplayImageOptions.Builder()
+                .cacheInMemory(true)
+                .imageScaleType(ImageScaleType.NONE)
+                .displayer(new FadeInBitmapDisplayer(100, true, true, false))
+                .bitmapConfig(Bitmap.Config.RGB_565)
+                .build();
     }
 
     void bindModel(@NonNull String categoryName) {
@@ -78,7 +92,7 @@ public class CategoryController extends RecyclerView.ViewHolder implements Loade
             image.setVisibility(View.GONE);
         } else {
             image.setVisibility(View.VISIBLE);
-            image.setImageDrawable(ContextCompat.getDrawable(activity, categoryImageId));
+            ImageLoader.getInstance().displayImage("drawable://" + categoryImageId, image, displayImageOptions);
         }
     }