Fixed back button exiting from app in full screen mode

app/src/main/java/it/danieleverducci/ojo/ui/MainActivity.java

@@ -8,6 +8,7 @@ import androidx.appcompat.app.AppCompatActivity;
 import android.util.Log;
 import android.view.View;
 
+import androidx.fragment.app.Fragment;
 import androidx.navigation.NavController;
 import androidx.navigation.Navigation;
 
@@ -21,6 +22,7 @@ public class MainActivity extends AppCompatActivity {
     private ActivityMainBinding binding;
     private NavController navController;
     private boolean rotationEnabledSetting;
+    private OnBackButtonPressedListener onBackButtonPressedListener;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
@@ -49,6 +51,17 @@ public class MainActivity extends AppCompatActivity {
         });
     }
 
+    public void setOnBackButtonPressedListener(OnBackButtonPressedListener onBackButtonPressedListener) {
+        this.onBackButtonPressedListener = onBackButtonPressedListener;
+    }
+
+    @Override
+    public void onBackPressed() {
+        if (this.onBackButtonPressedListener != null && this.onBackButtonPressedListener.onBackPressed())
+            return;
+        super.onBackPressed();
+    }
+
     public void navigateToFragment(int actionId) {
         navigateToFragment(actionId, null);
     }

app/src/main/java/it/danieleverducci/ojo/ui/OnBackButtonPressedListener.java

@@ -0,0 +1,5 @@
+package it.danieleverducci.ojo.ui;
+
+public interface OnBackButtonPressedListener {
+    public boolean onBackPressed();
+}

app/src/main/java/it/danieleverducci/ojo/ui/SurveillanceFragment.java

@@ -80,7 +80,6 @@ public class SurveillanceFragment extends Fragment {
 
         binding = FragmentSurveillanceBinding.inflate(inflater, container, false);
         return binding.getRoot();
-
     }
 
     @Override
@@ -106,12 +105,26 @@ public class SurveillanceFragment extends Fragment {
             }
         }
 
+        fullscreenCameraView = false;
         addAllCameras();
 
         // Start playback for all streams
         for (CameraView cv : cameraViews) {
             cv.startPlayback();
         }
+
+        // Register for back pressed events
+        ((MainActivity)getActivity()).setOnBackButtonPressedListener(new OnBackButtonPressedListener() {
+            @Override
+            public boolean onBackPressed() {
+                if(fullscreenCameraView && cameraViews.size() > 1) {
+                    fullscreenCameraView = false;
+                    showAllCameras();
+                    return true;
+                }
+                return false;
+            }
+        });
     }
 
     @Override