Fix loading of images in contributions list (#2932)

Author: maskaravivek

app/src/main/java/fr/free/nrw/commons/contributions/ContributionViewHolder.java

@@ -6,9 +6,14 @@
 import android.widget.ProgressBar;
 import android.widget.TextView;
 
+import androidx.collection.LruCache;
+
 import com.facebook.drawee.view.SimpleDraweeView;
 
+import org.apache.commons.lang3.StringUtils;
+
 import javax.inject.Inject;
+import javax.inject.Named;
 
 import butterknife.BindView;
 import butterknife.ButterKnife;
@@ -18,6 +23,7 @@
 import fr.free.nrw.commons.ViewHolder;
 import fr.free.nrw.commons.contributions.model.DisplayableContribution;
 import fr.free.nrw.commons.di.ApplicationlessInjection;
+import io.reactivex.android.schedulers.AndroidSchedulers;
 import io.reactivex.disposables.CompositeDisposable;
 import io.reactivex.disposables.Disposable;
 import io.reactivex.schedulers.Schedulers;
@@ -35,6 +41,10 @@ public class ContributionViewHolder implements ViewHolder<DisplayableContributio
     @Inject
     MediaDataExtractor mediaDataExtractor;
 
+    @Inject
+    @Named("thumbnail-cache")
+    LruCache<String, String> thumbnailCache;
+
     private DisplayableContribution contribution;
     private CompositeDisposable compositeDisposable = new CompositeDisposable();
 
@@ -89,15 +99,21 @@ public void bindModel(Context context, DisplayableContribution contribution) {
 
     /**
      * This method fetches the thumbnail url from file name
+     * If the thumbnail url is present in cache, then it is used otherwise API call is made to fetch the thumbnail
      * This can be removed once #2904 is in place and contribution contains all metadata beforehand
      * @param contribution
      */
     private void fetchAndDisplayThumbnail(DisplayableContribution contribution) {
+        if (!StringUtils.isBlank(thumbnailCache.get(contribution.getFilename()))) {
+            imageView.setImageURI(thumbnailCache.get(contribution.getFilename()));
+            return;
+        }
         Timber.d("Fetching thumbnail for %s", contribution.getFilename());
         Disposable disposable = mediaDataExtractor.getMediaFromFileName(contribution.getFilename())
                 .subscribeOn(Schedulers.io())
-                .observeOn(Schedulers.io())
+                .observeOn(AndroidSchedulers.mainThread())
                 .subscribe(media -> {
+                    thumbnailCache.put(contribution.getFilename(), media.getThumbUrl());
                     imageView.setImageURI(media.getThumbUrl());
                 });
         compositeDisposable.add(disposable);

app/src/main/java/fr/free/nrw/commons/di/CommonsApplicationModule.java

@@ -150,6 +150,7 @@ public DBOpenHelper provideDBOpenHelper(Context context) {
 
     @Provides
     @Singleton
+    @Named("thumbnail-cache")
     public LruCache<String, String> provideLruCache() {
         return new LruCache<>(1024);
     }