Move thread fragment from pane

app/src/main/java/eu/faircode/email/ActivityView.java

@@ -715,6 +715,27 @@ public class ActivityView extends ActivityBilling implements FragmentManager.OnB
             content_pane.setVisibility(duo || open_pane ? View.INVISIBLE : View.GONE);
         }
 
+        FragmentManager fm = getSupportFragmentManager();
+
+        int count = fm.getBackStackEntryCount();
+        if (count > 1 && "thread".equals(fm.getBackStackEntryAt(count - 1).getName())) {
+            Fragment fragment = fm.findFragmentByTag("thread");
+            if (fragment != null &&
+                    fragment.getId() == (content_pane == null ? R.id.content_pane : R.id.content_frame)) {
+                Log.i("Moving pane=" + (content_pane != null) + " fragment=" + fragment);
+                fm.popBackStack("thread", FragmentManager.POP_BACK_STACK_INCLUSIVE);
+                Fragment newFragment = Helper.recreateFragment(fragment, fm);
+                FragmentTransaction ft = fm.beginTransaction();
+                ft.replace(content_pane == null ? R.id.content_frame : R.id.content_pane, newFragment, "thread")
+                        .addToBackStack("thread");
+                ft.commit();
+                if (content_pane != null) {
+                    content_separator.setVisibility(View.VISIBLE);
+                    content_pane.setVisibility(View.VISIBLE);
+                }
+            }
+        }
+
         if (getSupportFragmentManager().getFragments().size() == 0 &&
                 !getIntent().hasExtra(Intent.EXTRA_PROCESS_TEXT))
             init();
@@ -2455,7 +2476,7 @@ public class ActivityView extends ActivityBilling implements FragmentManager.OnB
         }
 
         FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
-        fragmentTransaction.replace(pane, fragment).addToBackStack("thread");
+        fragmentTransaction.replace(pane, fragment, "thread").addToBackStack("thread");
         fragmentTransaction.commit();
     }
 

app/src/main/java/eu/faircode/email/FragmentMessages.java

@@ -6372,7 +6372,7 @@ public class FragmentMessages extends FragmentBase
         fragment.setArguments(args);
 
         FragmentTransaction fragmentTransaction = getParentFragmentManager().beginTransaction();
-        fragmentTransaction.replace(R.id.content_frame, fragment).addToBackStack("thread");
+        fragmentTransaction.replace(R.id.content_frame, fragment, "thread").addToBackStack("thread");
         fragmentTransaction.commit();
     }
 
@@ -7626,7 +7626,7 @@ public class FragmentMessages extends FragmentBase
                 int res = (pane ? R.id.content_pane : R.id.content_frame);
                 if (getActivity() != null && getActivity().findViewById(res) != null) {
                     FragmentTransaction fragmentTransaction = getParentFragmentManager().beginTransaction();
-                    fragmentTransaction.replace(res, fragment).addToBackStack("thread");
+                    fragmentTransaction.replace(res, fragment, "thread").addToBackStack("thread");
                     fragmentTransaction.commit();
                 }
             }

app/src/main/java/eu/faircode/email/Helper.java

@@ -122,6 +122,7 @@ import androidx.core.view.ViewCompat;
 import androidx.core.view.WindowInsetsCompat;
 import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentActivity;
+import androidx.fragment.app.FragmentManager;
 import androidx.lifecycle.Lifecycle;
 import androidx.lifecycle.LifecycleObserver;
 import androidx.lifecycle.LifecycleOwner;
@@ -1779,6 +1780,21 @@ public class Helper {
         return options.toBundle();
     }
 
+    static Fragment recreateFragment(Fragment fragment, FragmentManager fm) {
+        try {
+            Fragment.SavedState savedState = fm.saveFragmentInstanceState(fragment);
+            Bundle args = fragment.getArguments();
+
+            Fragment newFragment = fragment.getClass().newInstance();
+            newFragment.setInitialSavedState(savedState);
+            newFragment.setArguments(args);
+
+            return newFragment;
+        } catch (Throwable e) {
+            throw new RuntimeException("Cannot recreate fragment=" + fragment, e);
+        }
+    }
+
     // Graphics
 
     static int dp2pixels(Context context, int dp) {