Fix broken Picasso caching

app/src/main/java/app/insti/activity/MainActivity.java

@@ -37,6 +37,7 @@ import com.google.firebase.iid.InstanceIdResult;
 import com.google.gson.JsonObject;
 import com.squareup.picasso.Picasso;
 
+import java.io.File;
 import java.util.List;
 
 import app.insti.Constants;
@@ -66,6 +67,7 @@ import app.insti.fragment.QuickLinksFragment;
 import app.insti.fragment.SettingsFragment;
 import app.insti.fragment.TrainingBlogFragment;
 import app.insti.notifications.NotificationEventReceiver;
+import okhttp3.Cache;
 import okhttp3.OkHttpClient;
 import retrofit2.Call;
 import retrofit2.Callback;
@@ -545,8 +547,11 @@ public class MainActivity extends AppCompatActivity implements NavigationView.On
 
     public void initPicasso() {
         Picasso.Builder builder = new Picasso.Builder(getApplicationContext());
+        OkHttpClient.Builder client = new OkHttpClient.Builder();
+        Cache cache = new Cache(new File(getApplicationContext().getCacheDir(), "http-cache"), 100 * 1024 * 1024);
+        client.cache(cache);
         builder.downloader(new com.squareup.picasso.OkHttp3Downloader((
-                new OkHttpClient.Builder().build()
+                client.build()
         )));
         Picasso built = builder.build();
         built.setIndicatorsEnabled(false);