Added tablet landscape two column layout

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

@@ -81,7 +81,9 @@ import javax.net.ssl.HttpsURLConnection;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.appcompat.app.ActionBarDrawerToggle;
+import androidx.constraintlayout.widget.Group;
 import androidx.drawerlayout.widget.DrawerLayout;
+import androidx.fragment.app.Fragment;
 import androidx.fragment.app.FragmentManager;
 import androidx.fragment.app.FragmentTransaction;
 import androidx.lifecycle.Lifecycle;
@@ -92,6 +94,7 @@ import androidx.localbroadcastmanager.content.LocalBroadcastManager;
 public class ActivityView extends ActivityBilling implements FragmentManager.OnBackStackChangedListener {
     private View view;
     private DrawerLayout drawerLayout;
+    private Group grpPane;
     private ListView drawerList;
     private ActionBarDrawerToggle drawerToggle;
 
@@ -135,6 +138,8 @@ public class ActivityView extends ActivityBilling implements FragmentManager.OnB
         drawerLayout = findViewById(R.id.drawer_layout);
         drawerLayout.setScrimColor(Helper.resolveColor(this, R.attr.colorDrawerScrim));
 
+        grpPane = findViewById(R.id.grpPane);
+
         drawerToggle = new ActionBarDrawerToggle(this, drawerLayout, R.string.app_name, R.string.app_name) {
             public void onDrawerClosed(View view) {
                 super.onDrawerClosed(view);
@@ -422,6 +427,9 @@ public class ActivityView extends ActivityBilling implements FragmentManager.OnB
             if (drawerLayout.isDrawerOpen(drawerList))
                 drawerLayout.closeDrawer(drawerList);
             drawerToggle.setDrawerIndicatorEnabled(count == 1);
+
+            Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.content_pane);
+            grpPane.setVisibility(fragment == null ? View.GONE : View.VISIBLE);
         }
     }
 
@@ -862,8 +870,16 @@ public class ActivityView extends ActivityBilling implements FragmentManager.OnB
         FragmentMessages fragment = new FragmentMessages();
         fragment.setArguments(args);
 
+        int pane;
+        if (findViewById(R.id.content_pane) == null)
+            pane = R.id.content_frame;
+        else {
+            pane = R.id.content_pane;
+            grpPane.setVisibility(View.VISIBLE);
+        }
+
         FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
-        fragmentTransaction.replace(R.id.content_frame, fragment).addToBackStack("thread");
+        fragmentTransaction.replace(pane, fragment).addToBackStack("thread");
         fragmentTransaction.commit();
     }
 

app/src/main/res/layout-w600dp-land/activity_view.xml

@@ -0,0 +1,55 @@
+<androidx.drawerlayout.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:id="@+id/drawer_layout"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    tools:context=".ActivityView">
+
+    <androidx.constraintlayout.widget.ConstraintLayout
+        android:layout_width="match_parent"
+        android:layout_height="match_parent">
+
+        <FrameLayout
+            android:id="@+id/content_frame"
+            android:layout_width="0dp"
+            android:layout_height="match_parent"
+            app:layout_constraintEnd_toStartOf="@+id/content_separator"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toTopOf="parent" />
+
+        <View
+            android:id="@+id/content_separator"
+            android:layout_width="1dp"
+            android:layout_height="match_parent"
+            android:background="?attr/colorSeparator"
+            app:layout_constraintEnd_toStartOf="@+id/content_pane"
+            app:layout_constraintStart_toEndOf="@id/content_frame"
+            app:layout_constraintTop_toTopOf="parent" />
+
+        <FrameLayout
+            android:id="@+id/content_pane"
+            android:layout_width="0dp"
+            android:layout_height="match_parent"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toEndOf="@id/content_separator"
+            app:layout_constraintTop_toTopOf="parent" />
+
+        <androidx.constraintlayout.widget.Group
+            android:id="@+id/grpPane"
+            android:layout_width="0dp"
+            android:layout_height="0dp"
+            android:visibility="gone"
+            app:constraint_referenced_ids="content_separator,content_pane" />
+    </androidx.constraintlayout.widget.ConstraintLayout>
+
+    <ListView
+        android:id="@+id/drawer_list"
+        android:layout_width="270dp"
+        android:layout_height="match_parent"
+        android:layout_gravity="start"
+        android:background="?attr/colorDrawerBackground"
+        android:choiceMode="singleChoice"
+        android:divider="@android:color/transparent"
+        android:dividerHeight="0dp" />
+</androidx.drawerlayout.widget.DrawerLayout>