allow using the app as an image chooser

app/src/main/AndroidManifest.xml

@@ -18,6 +18,12 @@
 
                 <category android:name="android.intent.category.LAUNCHER"/>
             </intent-filter>
+
+            <intent-filter>
+                <action android:name="android.intent.action.PICK"/>
+                <category android:name="android.intent.category.DEFAULT"/>
+                <data android:mimeType="vnd.android.cursor.dir/image"/>
+            </intent-filter>
         </activity>
 
         <activity

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

@@ -3,4 +3,5 @@ package com.simplemobiletools.gallery;
 public class Constants {
     public static final String DIRECTORY = "directory";
     public static final String MEDIUM = "medium";
+    public static final String PICK_INTENT = "is_pick_intent";
 }

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

@@ -47,6 +47,7 @@ public class MainActivity extends AppCompatActivity
     @BindView(R.id.directories_grid) GridView gridView;
 
     private static final int STORAGE_PERMISSION = 1;
+    private static final int PICK_IMAGE = 2;
     private List<Directory> dirs;
     private int selectedItemsCnt;
     private Snackbar snackbar;
@@ -318,11 +319,27 @@ public class MainActivity extends AppCompatActivity
         });
     }
 
+    private boolean isPickIntent(Intent intent) {
+        return intent != null && intent.getAction() != null && intent.getAction().equals(Intent.ACTION_PICK);
+    }
+
+    @Override
+    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
+        if (requestCode == PICK_IMAGE && resultCode == RESULT_OK && data != null) {
+            final Intent result = new Intent();
+            result.setData(data.getData());
+            setResult(RESULT_OK, result);
+            finish();
+        }
+        super.onActivityResult(requestCode, resultCode, data);
+    }
+
     @Override
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
         final Intent intent = new Intent(this, MediaActivity.class);
         intent.putExtra(Constants.DIRECTORY, dirs.get(position).getPath());
-        startActivity(intent);
+        intent.putExtra(Constants.PICK_INTENT, isPickIntent(getIntent()));
+        startActivityForResult(intent, PICK_IMAGE);
     }
 
     @Override

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

@@ -234,10 +234,17 @@ public class MediaActivity extends AppCompatActivity
 
     @Override
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
+        if (getIntent().getBooleanExtra(Constants.PICK_INTENT, false)) {
+            final Intent result = new Intent();
+            result.setData(Uri.parse(media.get(position).getPath()));
+            setResult(RESULT_OK, result);
+            finish();
+        } else {
             final Intent intent = new Intent(this, ViewPagerActivity.class);
             intent.putExtra(Constants.MEDIUM, media.get(position).getPath());
             startActivity(intent);
         }
+    }
 
     @Override
     public void onItemCheckedStateChanged(ActionMode mode, int position, long id, boolean checked) {