Improve (un)registering FragmentLifecycleCallbacks

to avoid adding it multiple times and ensure proper cleanup

app/src/main/java/org/schabi/newpipe/RouterActivity.java

@@ -32,6 +32,7 @@ import androidx.appcompat.content.res.AppCompatResources;
 import androidx.core.app.NotificationCompat;
 import androidx.core.app.ServiceCompat;
 import androidx.core.math.MathUtils;
+import androidx.fragment.app.DialogFragment;
 import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentManager;
 import androidx.preference.PreferenceManager;
@@ -113,6 +114,7 @@ public class RouterActivity extends AppCompatActivity {
     private boolean selectionIsDownload = false;
     private boolean selectionIsAddToPlaylist = false;
     private AlertDialog alertDialogChoice = null;
+    private FragmentManager.FragmentLifecycleCallbacks dismissListener = null;
 
     @Override
     protected void onCreate(final Bundle savedInstanceState) {
@@ -142,6 +144,27 @@ public class RouterActivity extends AppCompatActivity {
         super.onCreate(savedInstanceState);
         Icepick.restoreInstanceState(this, savedInstanceState);
 
+        // FragmentManager will take care to recreate (Playlist|Download)Dialog when screen rotates
+        // We used to .setOnDismissListener(dialog -> finish()); when creating these DialogFragments
+        // but those callbacks won't survive a config change
+        // Try an alternate approach to hook into FragmentManager instead, to that effect
+        // (ref: https://stackoverflow.com/a/44028453)
+        final FragmentManager fm = getSupportFragmentManager();
+        if (dismissListener == null) {
+            dismissListener = new FragmentManager.FragmentLifecycleCallbacks() {
+                @Override
+                public void onFragmentDestroyed(@NonNull final FragmentManager fm,
+                                                @NonNull final Fragment f) {
+                    super.onFragmentDestroyed(fm, f);
+                    if (f instanceof DialogFragment && fm.getFragments().isEmpty()) {
+                        // No more DialogFragments, we're done
+                        finish();
+                    }
+                }
+            };
+        }
+        fm.registerFragmentLifecycleCallbacks(dismissListener, false);
+
         if (TextUtils.isEmpty(currentUrl)) {
             currentUrl = getUrl(getIntent());
 
@@ -171,29 +194,10 @@ public class RouterActivity extends AppCompatActivity {
     protected void onStart() {
         super.onStart();
 
-        // FragmentManager will take care to recreate DialogFragments when screen rotates
-        // currently that's namely PlaylistDialog or DownloadDialog
-        // We used to .setOnDismissListener(dialog ->finish()); when creating those Dialogs
-        // but those callbacks won't survive a config change
-        // Try an alternate approach to hook into FragmentManager instead, to that effect
-        // (courtesy of https://stackoverflow.com/a/44028453)
-        final FragmentManager fm = getSupportFragmentManager();
-        fm.registerFragmentLifecycleCallbacks(new FragmentManager.FragmentLifecycleCallbacks() {
-            @Override
-            public void onFragmentViewDestroyed(@NonNull final FragmentManager fm,
-                                                @NonNull final Fragment f) {
-                super.onFragmentViewDestroyed(fm, f);
-                if (fm.getFragments().isEmpty()) {
-                    // No more Dialog, we're done
-                    finish();
-                }
-            }
-        }, false);
-
         // Don't overlap the DialogFragment after rotating the screen
         // If there's no DialogFragment, we're either starting afresh
         // or we didn't make it to PlaylistDialog or DownloadDialog before the orientation change
-        if (fm.getFragments().isEmpty()) {
+        if (getSupportFragmentManager().getFragments().isEmpty()) {
             // Start over from scratch
             handleUrl(currentUrl);
         }
@@ -203,6 +207,9 @@ public class RouterActivity extends AppCompatActivity {
     protected void onDestroy() {
         super.onDestroy();
 
+        if (dismissListener != null) {
+            getSupportFragmentManager().unregisterFragmentLifecycleCallbacks(dismissListener);
+        }
         disposables.clear();
     }