use interfaces for communicating with fragments

app/src/main/java/com/simplemobiletools/gallery/activities/ViewPagerActivity.java

@@ -24,6 +24,7 @@ import com.simplemobiletools.gallery.MyViewPager;
 import com.simplemobiletools.gallery.R;
 import com.simplemobiletools.gallery.Utils;
 import com.simplemobiletools.gallery.adapters.MyPagerAdapter;
+import com.simplemobiletools.gallery.fragments.ViewPagerFragment;
 import com.simplemobiletools.gallery.models.Medium;
 
 import java.io.File;
@@ -36,7 +37,8 @@ import butterknife.ButterKnife;
 import butterknife.OnClick;
 
 public class ViewPagerActivity extends AppCompatActivity
-        implements ViewPager.OnPageChangeListener, View.OnSystemUiVisibilityChangeListener, ViewPager.OnTouchListener {
+        implements ViewPager.OnPageChangeListener, View.OnSystemUiVisibilityChangeListener, ViewPager.OnTouchListener,
+        ViewPagerFragment.FragmentClickListener {
     @BindView(R.id.undo_delete) View undoBtn;
     @BindView(R.id.view_pager) MyViewPager pager;
 
@@ -76,7 +78,7 @@ public class ViewPagerActivity extends AppCompatActivity
         if (isDirEmpty())
             return;
 
-        final MyPagerAdapter adapter = new MyPagerAdapter(getSupportFragmentManager(), media);
+        final MyPagerAdapter adapter = new MyPagerAdapter(this, getSupportFragmentManager(), media);
         pager.setAdapter(adapter);
         pager.setCurrentItem(pos);
         pager.addOnPageChangeListener(this);
@@ -301,6 +303,7 @@ public class ViewPagerActivity extends AppCompatActivity
         return myMedia;
     }
 
+    @Override
     public void fragmentClicked() {
         deleteFile();
         isFullScreen = !isFullScreen;

app/src/main/java/com/simplemobiletools/gallery/adapters/MyPagerAdapter.java

@@ -6,6 +6,7 @@ import android.support.v4.app.FragmentManager;
 import android.support.v4.app.FragmentStatePagerAdapter;
 
 import com.simplemobiletools.gallery.Constants;
+import com.simplemobiletools.gallery.activities.ViewPagerActivity;
 import com.simplemobiletools.gallery.fragments.PhotoFragment;
 import com.simplemobiletools.gallery.fragments.VideoFragment;
 import com.simplemobiletools.gallery.fragments.ViewPagerFragment;
@@ -18,9 +19,11 @@ import java.util.Map;
 public class MyPagerAdapter extends FragmentStatePagerAdapter {
     private List<Medium> media;
     private Map<Integer, ViewPagerFragment> fragments;
+    private ViewPagerActivity activity;
 
-    public MyPagerAdapter(FragmentManager fm, List<Medium> media) {
+    public MyPagerAdapter(ViewPagerActivity act, FragmentManager fm, List<Medium> media) {
         super(fm);
+        this.activity = act;
         this.media = media;
         fragments = new HashMap<>();
     }
@@ -45,6 +48,7 @@ public class MyPagerAdapter extends FragmentStatePagerAdapter {
 
         fragments.put(position, fragment);
         fragment.setArguments(bundle);
+        fragment.setListener(activity);
         return fragment;
     }
 

app/src/main/java/com/simplemobiletools/gallery/fragments/PhotoFragment.java

@@ -9,7 +9,6 @@ import com.davemorrissey.labs.subscaleview.ImageSource;
 import com.davemorrissey.labs.subscaleview.SubsamplingScaleImageView;
 import com.simplemobiletools.gallery.Constants;
 import com.simplemobiletools.gallery.R;
-import com.simplemobiletools.gallery.activities.ViewPagerActivity;
 import com.simplemobiletools.gallery.models.Medium;
 
 public class PhotoFragment extends ViewPagerFragment implements View.OnClickListener {
@@ -38,7 +37,7 @@ public class PhotoFragment extends ViewPagerFragment implements View.OnClickList
 
     @Override
     public void onClick(View v) {
-        ((ViewPagerActivity) getActivity()).fragmentClicked();
+        listener.fragmentClicked();
     }
 
     @Override

app/src/main/java/com/simplemobiletools/gallery/fragments/VideoFragment.java

@@ -24,7 +24,6 @@ import android.widget.TextView;
 import com.simplemobiletools.gallery.Constants;
 import com.simplemobiletools.gallery.R;
 import com.simplemobiletools.gallery.Utils;
-import com.simplemobiletools.gallery.activities.ViewPagerActivity;
 import com.simplemobiletools.gallery.models.Medium;
 
 import java.io.IOException;
@@ -157,7 +156,7 @@ public class VideoFragment extends ViewPagerFragment
             default:
                 isFullscreen = !isFullscreen;
                 checkFullscreen();
-                ((ViewPagerActivity) getActivity()).fragmentClicked();
+                listener.fragmentClicked();
                 break;
         }
     }

app/src/main/java/com/simplemobiletools/gallery/fragments/ViewPagerFragment.java

@@ -3,7 +3,17 @@ package com.simplemobiletools.gallery.fragments;
 import android.support.v4.app.Fragment;
 
 public abstract class ViewPagerFragment extends Fragment {
+    protected FragmentClickListener listener;
+
+    public void setListener(FragmentClickListener ln) {
+        listener = ln;
+    }
+
     public abstract void itemDragged();
 
     public abstract void systemUiVisibilityChanged(boolean toFullscreen);
+
+    public interface FragmentClickListener {
+        void fragmentClicked();
+    }
 }