Use bottom bar for previous/next navigation

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

@@ -74,6 +74,7 @@ import androidx.fragment.app.FragmentManager;
 import androidx.fragment.app.FragmentTransaction;
 import androidx.lifecycle.Lifecycle;
 import androidx.lifecycle.Observer;
+import androidx.lifecycle.ViewModelProviders;
 import androidx.localbroadcastmanager.content.LocalBroadcastManager;
 import androidx.paging.PagedList;
 
@@ -303,8 +304,10 @@ public class ActivityView extends ActivityBilling implements FragmentManager.OnB
             intent.setAction(null);
             setIntent(intent);
 
+            ViewModelMessages model = ViewModelProviders.of(this).get(ViewModelMessages.class);
+            model.setMessages(null);
+
             intent.putExtra("thread", action.split(":", 2)[1]);
-            getSupportFragmentManager().popBackStack("unified", 0);
             onViewThread(intent);
         }
     }
@@ -767,6 +770,8 @@ public class ActivityView extends ActivityBilling implements FragmentManager.OnB
     }
 
     private void onViewThread(Intent intent) {
+        getSupportFragmentManager().popBackStack("thread", FragmentManager.POP_BACK_STACK_INCLUSIVE);
+
         Bundle args = new Bundle();
         args.putLong("account", intent.getLongExtra("account", -1));
         args.putString("thread", intent.getStringExtra("thread"));

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

@@ -39,6 +39,7 @@ import android.widget.ImageButton;
 import android.widget.ProgressBar;
 import android.widget.TextView;
 
+import com.google.android.material.bottomnavigation.BottomNavigationView;
 import com.google.android.material.floatingactionbutton.FloatingActionButton;
 import com.google.android.material.snackbar.Snackbar;
 
@@ -56,6 +57,7 @@ import androidx.fragment.app.FragmentTransaction;
 import androidx.lifecycle.Lifecycle;
 import androidx.lifecycle.LiveData;
 import androidx.lifecycle.Observer;
+import androidx.lifecycle.ViewModelProviders;
 import androidx.localbroadcastmanager.content.LocalBroadcastManager;
 import androidx.paging.LivePagedListBuilder;
 import androidx.paging.PagedList;
@@ -70,6 +72,7 @@ public class FragmentMessages extends FragmentEx {
     private ImageButton ibHintActions;
     private RecyclerView rvMessage;
     private TextView tvNoEmail;
+    private BottomNavigationView bottom_navigation;
     private ProgressBar pbWait;
     private Group grpSupport;
     private Group grpHintSupport;
@@ -139,6 +142,7 @@ public class FragmentMessages extends FragmentEx {
         ibHintActions = view.findViewById(R.id.ibHintActions);
         rvMessage = view.findViewById(R.id.rvFolder);
         tvNoEmail = view.findViewById(R.id.tvNoEmail);
+        bottom_navigation = view.findViewById(R.id.bottom_navigation);
         pbWait = view.findViewById(R.id.pbWait);
         grpSupport = view.findViewById(R.id.grpSupport);
         grpHintSupport = view.findViewById(R.id.grpHintSupport);
@@ -457,6 +461,20 @@ public class FragmentMessages extends FragmentEx {
             }
         }).attachToRecyclerView(rvMessage);
 
+        bottom_navigation.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
+            @Override
+            public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
+                String[] pn = (String[]) bottom_navigation.getTag();
+                String thread = (menuItem.getItemId() == R.id.action_prev ? pn[0] : pn[1]);
+                LocalBroadcastManager lbm = LocalBroadcastManager.getInstance(getContext());
+                lbm.sendBroadcast(
+                        new Intent(ActivityView.ACTION_VIEW_THREAD)
+                                .putExtra("account", account)
+                                .putExtra("thread", thread));
+                return true;
+            }
+        });
+
         fab.setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View view) {
@@ -467,19 +485,9 @@ public class FragmentMessages extends FragmentEx {
             }
         });
 
-        View.OnClickListener navigate = new View.OnClickListener() {
-            @Override
-            public void onClick(View v) {
-                LocalBroadcastManager lbm = LocalBroadcastManager.getInstance(getContext());
-                lbm.sendBroadcast(
-                        new Intent(ActivityView.ACTION_VIEW_THREAD)
-                                .putExtra("account", account)
-                                .putExtra("thread", (String) v.getTag()));
-            }
-        };
-
         // Initialize
         tvNoEmail.setVisibility(View.GONE);
+        bottom_navigation.setVisibility(View.GONE);
         grpReady.setVisibility(View.GONE);
         pbWait.setVisibility(View.VISIBLE);
 
@@ -576,8 +584,16 @@ public class FragmentMessages extends FragmentEx {
         // Messages
         loadMessages();
 
-        // Compose FAB
-        if (viewType != AdapterMessage.ViewType.THREAD) {
+        if (viewType == AdapterMessage.ViewType.THREAD) {
+            // Navigation
+            ViewModelMessages model = ViewModelProviders.of(getActivity()).get(ViewModelMessages.class);
+            String[] pn = model.getPrevNext(thread);
+            bottom_navigation.setTag(pn);
+            bottom_navigation.getMenu().findItem(R.id.action_prev).setEnabled(pn[0] != null);
+            bottom_navigation.getMenu().findItem(R.id.action_next).setEnabled(pn[1] != null);
+            bottom_navigation.setVisibility(pn[0] == null && pn[1] == null ? View.GONE : View.VISIBLE);
+        } else {
+            // Compose FAB
             Bundle args = new Bundle();
             args.putLong("account", account);
 
@@ -832,7 +848,7 @@ public class FragmentMessages extends FragmentEx {
                     return;
                 }
 
-                if (viewType == AdapterMessage.ViewType.THREAD)
+                if (viewType == AdapterMessage.ViewType.THREAD) {
                     if (autoExpand) {
                         autoExpand = false;
 
@@ -886,6 +902,10 @@ public class FragmentMessages extends FragmentEx {
                                 finish();
                         }
                     }
+                } else {
+                    ViewModelMessages model = ViewModelProviders.of(getActivity()).get(ViewModelMessages.class);
+                    model.setMessages(messages);
+                }
 
                 Log.i(Helper.TAG, "Submit messages=" + messages.size());
                 adapter.submitList(messages);

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

@@ -0,0 +1,36 @@
+package eu.faircode.email;
+
+import androidx.lifecycle.ViewModel;
+import androidx.paging.PagedList;
+
+public class ViewModelMessages extends ViewModel {
+    private PagedList<TupleMessageEx> messages = null;
+
+    void setMessages(PagedList<TupleMessageEx> messages) {
+        this.messages = messages;
+    }
+
+    String[] getPrevNext(String thread) {
+        if (messages == null)
+            return new String[]{null, null};
+
+        boolean found = false;
+        TupleMessageEx prev = null;
+        TupleMessageEx next = null;
+        for (int i = 0; i < messages.size(); i++) {
+            TupleMessageEx item = messages.get(i);
+            if (item == null)
+                continue;
+            if (found) {
+                next = item;
+                messages.loadAround(i);
+                break;
+            }
+            if (thread.equals(item.thread))
+                found = true;
+            else
+                prev = item;
+        }
+        return new String[]{prev == null ? null : prev.thread, next == null ? null : next.thread};
+    }
+}

app/src/main/res/drawable/baseline_navigate_before_24.xml

@@ -0,0 +1,10 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="24dp"
+        android:height="24dp"
+        android:viewportWidth="24.0"
+        android:viewportHeight="24.0"
+        android:tint="?attr/colorControlNormal">
+    <path
+        android:fillColor="@android:color/white"
+        android:pathData="M15.41,7.41L14,6l-6,6 6,6 1.41,-1.41L10.83,12z"/>
+</vector>

app/src/main/res/drawable/baseline_navigate_next_24.xml

@@ -0,0 +1,10 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="24dp"
+        android:height="24dp"
+        android:viewportWidth="24.0"
+        android:viewportHeight="24.0"
+        android:tint="?attr/colorControlNormal">
+    <path
+        android:fillColor="@android:color/white"
+        android:pathData="M10,6L8.59,7.41 13.17,12l-4.58,4.59L10,18l6,-6z"/>
+</vector>

app/src/main/res/layout/fragment_messages.xml

@@ -110,7 +110,7 @@
             android:layout_height="0dp"
             android:scrollbarStyle="outsideOverlay"
             android:scrollbars="vertical"
-            app:layout_constraintBottom_toBottomOf="parent"
+            app:layout_constraintBottom_toTopOf="@+id/bottom_navigation"
             app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintStart_toStartOf="parent"
             app:layout_constraintTop_toBottomOf="@id/vSeparatorHintActions" />
@@ -126,6 +126,19 @@
             app:layout_constraintStart_toStartOf="parent"
             app:layout_constraintTop_toTopOf="parent" />
 
+        <com.google.android.material.bottomnavigation.BottomNavigationView
+            android:id="@+id/bottom_navigation"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:background="@color/colorPrimary"
+            app:itemIconTint="@color/bottomnav_background"
+            app:itemTextColor="@color/bottomnav_background"
+            app:labelVisibilityMode="unlabeled"
+            app:layout_constraintBottom_toBottomOf="parent"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toStartOf="parent"
+            app:menu="@menu/action_messages" />
+
         <androidx.constraintlayout.widget.Group
             android:id="@+id/grpSupport"
             android:layout_width="0dp"

app/src/main/res/menu/action_messages.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="utf-8"?>
+<menu xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <item
+        android:id="@+id/action_prev"
+        android:icon="@drawable/baseline_navigate_before_24"
+        android:title="" />
+
+    <item
+        android:id="@+id/action_next"
+        android:icon="@drawable/baseline_navigate_next_24"
+        android:title="" />
+</menu>