lets use subsampling-scale-image-view for proper zooming

app/build.gradle

@@ -24,5 +24,5 @@ dependencies {
     testCompile 'junit:junit:4.12'
     compile 'com.android.support:appcompat-v7:23.1.1'
     compile 'com.github.bumptech.glide:glide:3.7.0'
-    compile 'com.commit451:PhotoView:1.2.4'
+    compile 'com.davemorrissey.labs:subsampling-scale-image-view:3.4.1'
 }

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

@@ -0,0 +1,30 @@
+package gallery.simplemobiletools.com;
+
+import android.os.Bundle;
+import android.support.v4.app.Fragment;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+
+import com.davemorrissey.labs.subscaleview.ImageSource;
+import com.davemorrissey.labs.subscaleview.SubsamplingScaleImageView;
+
+public class ViewPagerFragment extends Fragment {
+    private String path;
+
+    public void setPath(String path) {
+        this.path = path;
+    }
+
+    @Override
+    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
+        final View view = inflater.inflate(R.layout.pager_item, container, false);
+
+        if (path != null) {
+            final SubsamplingScaleImageView imageView = (SubsamplingScaleImageView) view.findViewById(R.id.photo);
+            imageView.setImage(ImageSource.uri(path));
+        }
+
+        return view;
+    }
+}

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

@@ -26,7 +26,8 @@ public class ViewPagerActivity extends AppCompatActivity {
 
         pos = 0;
         final MyViewPager pager = (MyViewPager) findViewById(R.id.view_pager);
-        final MyPagerAdapter adapter = new MyPagerAdapter(this, getPhotos());
+        final MyPagerAdapter adapter = new MyPagerAdapter(getSupportFragmentManager());
+        adapter.setPaths(getPhotos());
         pager.setAdapter(adapter);
         pager.setCurrentItem(pos);
     }

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

@@ -1,22 +1,21 @@
 package gallery.simplemobiletools.com.adapters;
 
-import android.content.Context;
-import android.support.v4.view.PagerAdapter;
-import android.view.View;
-import android.view.ViewGroup;
-
-import com.bumptech.glide.Glide;
+import android.support.v4.app.Fragment;
+import android.support.v4.app.FragmentManager;
+import android.support.v4.app.FragmentStatePagerAdapter;
 
 import java.util.List;
 
-import uk.co.senab.photoview.PhotoView;
+import gallery.simplemobiletools.com.ViewPagerFragment;
 
-public class MyPagerAdapter extends PagerAdapter {
-    private final Context context;
-    private final List<String> paths;
+public class MyPagerAdapter extends FragmentStatePagerAdapter {
+    private List<String> paths;
 
-    public MyPagerAdapter(Context context, List<String> paths) {
-        this.context = context;
+    public MyPagerAdapter(FragmentManager fm) {
+        super(fm);
+    }
+
+    public void setPaths(List<String> paths) {
         this.paths = paths;
     }
 
@@ -26,21 +25,9 @@ public class MyPagerAdapter extends PagerAdapter {
     }
 
     @Override
-    public boolean isViewFromObject(View view, Object object) {
-        return view == object;
-    }
-
-    @Override
-    public Object instantiateItem(ViewGroup container, int position) {
-        final PhotoView photoView = new PhotoView(context);
-        Glide.with(context).load(paths.get(position)).fitCenter().crossFade().into(photoView);
-        container.addView(photoView);
-        photoView.setMaximumScale(20f);
-        return photoView;
-    }
-
-    @Override
-    public void destroyItem(ViewGroup container, int position, Object object) {
-        container.removeView((View) object);
+    public Fragment getItem(int position) {
+        final ViewPagerFragment fragment = new ViewPagerFragment();
+        fragment.setPath(paths.get(position));
+        return fragment;
     }
 }

app/src/main/res/layout/pager_item.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8"?>
+<com.davemorrissey.labs.subscaleview.SubsamplingScaleImageView
+    android:id="@+id/photo"
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"/>