Add an invite button in the new conversation screen.

res/drawable/ic_invite_24dp.xml

@@ -0,0 +1,5 @@
+<vector android:height="24dp" android:tint="@color/core_grey_75"
+    android:viewportHeight="24.0" android:viewportWidth="24.0"
+    android:width="24dp" xmlns:android="http://schemas.android.com/apk/res/android">
+    <path android:fillColor="#FF000000" android:pathData="M20,4L4,4c-1.1,0 -1.99,0.9 -1.99,2L2,18c0,1.1 0.9,2 2,2h16c1.1,0 2,-0.9 2,-2L22,6c0,-1.1 -0.9,-2 -2,-2zM20,18L4,18L4,8l8,5 8,-5v10zM12,11L4,6h16l-8,5z"/>
+</vector>

res/drawable/ic_invite_circle.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="utf-8"?>
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item>
+        <shape android:shape="oval">
+            <solid android:color="#eeefef" />
+        </shape>
+    </item>
+    <item
+        android:bottom="12dp"
+        android:drawable="@drawable/ic_invite_24dp"
+        android:left="12dp"
+        android:right="12dp"
+        android:top="12dp" />
+</layer-list>

res/layout/contact_selection_invite_action_item.xml

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="utf-8"?>
+<TextView xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
+    style="@style/Signal.Text.Body"
+    android:layout_width="match_parent"
+    android:layout_height="@dimen/contact_selection_item_height"
+    android:drawableStart="@drawable/ic_invite_circle"
+    android:drawablePadding="16dp"
+    android:ellipsize="marquee"
+    android:fontFamily="sans-serif-medium"
+    android:gravity="center_vertical|start"
+    android:labelFor="@id/action_icon"
+    android:paddingStart="@dimen/selection_item_header_width"
+    android:singleLine="true"
+    android:text="@string/contact_selection_activity__invite_to_signal"
+    android:textAlignment="viewStart"
+    tools:ignore="RtlSymmetry" />

res/values/strings.xml

@@ -933,6 +933,7 @@
 
     <!-- contact_selection_activity -->
     <string name="contact_selection_activity__enter_name_or_number">Enter name or number</string>
+    <string name="contact_selection_activity__invite_to_signal">Invite to Signal</string>
 
     <!-- contact_filter_toolbar -->
     <string name="contact_filter_toolbar__clear_entered_text_description">Clear entered text</string>

src/org/thoughtcrime/securesms/ContactSelectionListFragment.java

@@ -19,16 +19,10 @@ package org.thoughtcrime.securesms;
 
 import android.Manifest;
 import android.annotation.SuppressLint;
+import android.content.Context;
 import android.database.Cursor;
 import android.os.AsyncTask;
 import android.os.Bundle;
-import androidx.annotation.NonNull;
-import androidx.fragment.app.Fragment;
-import androidx.loader.app.LoaderManager;
-import androidx.loader.content.Loader;
-import androidx.swiperefreshlayout.widget.SwipeRefreshLayout;
-import androidx.recyclerview.widget.LinearLayoutManager;
-import androidx.recyclerview.widget.RecyclerView;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
@@ -37,6 +31,15 @@ import android.widget.Button;
 import android.widget.TextView;
 import android.widget.Toast;
 
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.fragment.app.Fragment;
+import androidx.loader.app.LoaderManager;
+import androidx.loader.content.Loader;
+import androidx.recyclerview.widget.LinearLayoutManager;
+import androidx.recyclerview.widget.RecyclerView;
+import androidx.swiperefreshlayout.widget.SwipeRefreshLayout;
+
 import com.pnikosis.materialishprogress.ProgressWheel;
 
 import org.thoughtcrime.securesms.components.RecyclerViewFastScroller;
@@ -44,7 +47,6 @@ import org.thoughtcrime.securesms.contacts.ContactSelectionListAdapter;
 import org.thoughtcrime.securesms.contacts.ContactSelectionListItem;
 import org.thoughtcrime.securesms.contacts.ContactsCursorLoader;
 import org.thoughtcrime.securesms.contacts.ContactsCursorLoader.DisplayMode;
-import org.thoughtcrime.securesms.database.CursorRecyclerViewAdapter;
 import org.thoughtcrime.securesms.logging.Log;
 import org.thoughtcrime.securesms.mms.GlideApp;
 import org.thoughtcrime.securesms.permissions.Permissions;
@@ -52,6 +54,8 @@ import org.thoughtcrime.securesms.util.DirectoryHelper;
 import org.thoughtcrime.securesms.util.StickyHeaderDecoration;
 import org.thoughtcrime.securesms.util.TextSecurePreferences;
 import org.thoughtcrime.securesms.util.ViewUtil;
+import org.thoughtcrime.securesms.util.adapter.FixedViewsAdapter;
+import org.thoughtcrime.securesms.util.adapter.RecyclerViewConcatenateAdapterStickyHeader;
 
 import java.io.IOException;
 import java.util.LinkedList;
@@ -64,28 +68,41 @@ import java.util.Set;
  * @author Moxie Marlinspike
  *
  */
-public class ContactSelectionListFragment extends    Fragment
+public final class ContactSelectionListFragment extends    Fragment
-                                          implements LoaderManager.LoaderCallbacks<Cursor>
+                                                implements LoaderManager.LoaderCallbacks<Cursor>
 {
   @SuppressWarnings("unused")
-  private static final String TAG = ContactSelectionListFragment.class.getSimpleName();
+  private static final String TAG = Log.tag(ContactSelectionListFragment.class);
 
   public static final String DISPLAY_MODE = "display_mode";
   public static final String MULTI_SELECT = "multi_select";
   public static final String REFRESHABLE  = "refreshable";
   public static final String RECENTS      = "recents";
 
-  private TextView                  emptyText;
+  private TextView                    emptyText;
-  private Set<String>               selectedContacts;
+  private Set<String>                 selectedContacts;
-  private OnContactSelectedListener onContactSelectedListener;
+  private OnContactSelectedListener   onContactSelectedListener;
-  private SwipeRefreshLayout        swipeRefresh;
+  private SwipeRefreshLayout          swipeRefresh;
-  private View                      showContactsLayout;
+  private View                        showContactsLayout;
-  private Button                    showContactsButton;
+  private Button                      showContactsButton;
-  private TextView                  showContactsDescription;
+  private TextView                    showContactsDescription;
-  private ProgressWheel             showContactsProgress;
+  private ProgressWheel               showContactsProgress;
-  private String                    cursorFilter;
+  private String                      cursorFilter;
-  private RecyclerView              recyclerView;
+  private RecyclerView                recyclerView;
-  private RecyclerViewFastScroller  fastScroller;
+  private RecyclerViewFastScroller    fastScroller;
+  private ContactSelectionListAdapter cursorRecyclerViewAdapter;
+
+  @Nullable private FixedViewsAdapter footerAdapter;
+  @Nullable private InviteCallback    inviteCallback;
+
+  @Override
+  public void onAttach(@NonNull Context context) {
+    super.onAttach(context);
+
+    if (context instanceof InviteCallback) {
+      inviteCallback = (InviteCallback) context;
+    }
+  }
 
   @Override
   public void onActivityCreated(Bundle icicle) {
@@ -158,14 +175,31 @@ public class ContactSelectionListFragment extends    Fragment
   }
 
   private void initializeCursor() {
-    ContactSelectionListAdapter adapter = new ContactSelectionListAdapter(getActivity(),
+    cursorRecyclerViewAdapter = new ContactSelectionListAdapter(requireContext(),
-                                                                          GlideApp.with(this),
+                                                                GlideApp.with(this),
-                                                                          null,
+                                                                null,
-                                                                          new ListClickListener(),
+                                                                new ListClickListener(),
-                                                                          isMulti());
+                                                                isMulti());
-    selectedContacts = adapter.getSelectedContacts();
+    selectedContacts = cursorRecyclerViewAdapter.getSelectedContacts();
-    recyclerView.setAdapter(adapter);
+
-    recyclerView.addItemDecoration(new StickyHeaderDecoration(adapter, true, true));
+    RecyclerViewConcatenateAdapterStickyHeader concatenateAdapter = new RecyclerViewConcatenateAdapterStickyHeader();
+
+    concatenateAdapter.addAdapter(cursorRecyclerViewAdapter);
+    if (inviteCallback != null) {
+      footerAdapter = new FixedViewsAdapter(createInviteActionView(inviteCallback));
+      footerAdapter.hide();
+      concatenateAdapter.addAdapter(footerAdapter);
+    }
+
+    recyclerView.setAdapter(concatenateAdapter);
+    recyclerView.addItemDecoration(new StickyHeaderDecoration(concatenateAdapter, true, true));
+  }
+
+  private View createInviteActionView(@NonNull InviteCallback inviteCallback) {
+    View view = LayoutInflater.from(requireContext())
+                              .inflate(R.layout.contact_selection_invite_action_item, (ViewGroup) requireView(), false);
+    view.setOnClickListener(v -> inviteCallback.onInvite());
+    return view;
   }
 
   private void initializeNoContactsPermission() {
@@ -192,7 +226,7 @@ public class ContactSelectionListFragment extends    Fragment
 
   public void setQueryFilter(String filter) {
     this.cursorFilter = filter;
-    this.getLoaderManager().restartLoader(0, null, this);
+    LoaderManager.getInstance(this).restartLoader(0, null, this);
   }
 
   public void resetQueryFilter() {
@@ -224,9 +258,14 @@ public class ContactSelectionListFragment extends    Fragment
     swipeRefresh.setVisibility(View.VISIBLE);
     showContactsLayout.setVisibility(View.GONE);
 
-    ((CursorRecyclerViewAdapter) recyclerView.getAdapter()).changeCursor(data);
+    cursorRecyclerViewAdapter.changeCursor(data);
+
+    if (footerAdapter != null) {
+      footerAdapter.show();
+    }
+
     emptyText.setText(R.string.contact_selection_group_activity__no_contacts);
-    boolean useFastScroller = (recyclerView.getAdapter().getItemCount() > 20);
+    boolean useFastScroller = data.getCount() > 20;
     recyclerView.setVerticalScrollBarEnabled(!useFastScroller);
     if (useFastScroller) {
       fastScroller.setVisibility(View.VISIBLE);
@@ -239,7 +278,7 @@ public class ContactSelectionListFragment extends    Fragment
 
   @Override
   public void onLoaderReset(@NonNull Loader<Cursor> loader) {
-    ((CursorRecyclerViewAdapter) recyclerView.getAdapter()).changeCursor(null);
+    cursorRecyclerViewAdapter.changeCursor(null);
     fastScroller.setVisibility(View.GONE);
   }
 
@@ -309,4 +348,7 @@ public class ContactSelectionListFragment extends    Fragment
     void onContactDeselected(String number);
   }
 
+  public interface InviteCallback {
+    void onInvite();
+  }
 }

src/org/thoughtcrime/securesms/MediaDocumentsAdapter.java

@@ -93,7 +93,7 @@ public class MediaDocumentsAdapter extends CursorRecyclerViewAdapter<ViewHolder>
   }
 
   @Override
-  public HeaderViewHolder onCreateHeaderViewHolder(ViewGroup parent) {
+  public HeaderViewHolder onCreateHeaderViewHolder(ViewGroup parent, int position) {
     return new HeaderViewHolder(LayoutInflater.from(getContext()).inflate(R.layout.media_overview_document_item_header, parent, false));
   }
 

src/org/thoughtcrime/securesms/NewConversationActivity.java

@@ -35,7 +35,9 @@ import org.thoughtcrime.securesms.recipients.Recipient;
  * @author Moxie Marlinspike
  *
  */
-public class NewConversationActivity extends ContactSelectionActivity {
+public class NewConversationActivity extends ContactSelectionActivity
+                                    implements ContactSelectionListFragment.InviteCallback
+{
 
   @SuppressWarnings("unused")
   private static final String TAG = NewConversationActivity.class.getSimpleName();
@@ -99,4 +101,9 @@ public class NewConversationActivity extends ContactSelectionActivity {
     super.onPrepareOptionsMenu(menu);
     return true;
   }
+
+  @Override
+  public void onInvite() {
+    handleInvite();
+  }
 }

src/org/thoughtcrime/securesms/contacts/ContactSelectionListAdapter.java

@@ -37,6 +37,7 @@ import org.thoughtcrime.securesms.components.RecyclerViewFastScroller.FastScroll
 import org.thoughtcrime.securesms.contacts.ContactSelectionListAdapter.HeaderViewHolder;
 import org.thoughtcrime.securesms.contacts.ContactSelectionListAdapter.ViewHolder;
 import org.thoughtcrime.securesms.database.CursorRecyclerViewAdapter;
+import org.thoughtcrime.securesms.logging.Log;
 import org.thoughtcrime.securesms.mms.GlideRequests;
 import org.thoughtcrime.securesms.util.StickyHeaderDecoration.StickyHeaderAdapter;
 import org.thoughtcrime.securesms.util.Util;
@@ -53,7 +54,8 @@ public class ContactSelectionListAdapter extends CursorRecyclerViewAdapter<ViewH
                                          implements FastScrollAdapter,
                                                     StickyHeaderAdapter<HeaderViewHolder>
 {
-  private final static String TAG = ContactSelectionListAdapter.class.getSimpleName();
+  @SuppressWarnings("unused")
+  private final static String TAG = Log.tag(ContactSelectionListAdapter.class);
 
   private static final int VIEW_TYPE_CONTACT = 0;
   private static final int VIEW_TYPE_DIVIDER = 1;
@@ -198,7 +200,7 @@ public class ContactSelectionListAdapter extends CursorRecyclerViewAdapter<ViewH
 
 
   @Override
-  public HeaderViewHolder onCreateHeaderViewHolder(ViewGroup parent) {
+  public HeaderViewHolder onCreateHeaderViewHolder(ViewGroup parent, int position) {
     return new HeaderViewHolder(LayoutInflater.from(getContext()).inflate(R.layout.contact_selection_recyclerview_header, parent, false));
   }
 

src/org/thoughtcrime/securesms/conversation/ConversationAdapter.java

@@ -414,7 +414,7 @@ public class ConversationAdapter <V extends View & BindableConversationItem>
   }
 
   @Override
-  public HeaderViewHolder onCreateHeaderViewHolder(ViewGroup parent) {
+  public HeaderViewHolder onCreateHeaderViewHolder(ViewGroup parent, int position) {
     return new HeaderViewHolder(LayoutInflater.from(getContext()).inflate(R.layout.conversation_item_header, parent, false));
   }
 

src/org/thoughtcrime/securesms/search/SearchListAdapter.java

@@ -94,7 +94,7 @@ class SearchListAdapter extends    RecyclerView.Adapter<SearchListAdapter.Search
   }
 
   @Override
-  public HeaderViewHolder onCreateHeaderViewHolder(ViewGroup parent) {
+  public HeaderViewHolder onCreateHeaderViewHolder(ViewGroup parent, int position) {
     return new HeaderViewHolder(LayoutInflater.from(parent.getContext())
                                               .inflate(R.layout.contact_selection_list_divider, parent, false));
   }

src/org/thoughtcrime/securesms/util/StickyHeaderDecoration.java

@@ -88,7 +88,7 @@ public class StickyHeaderDecoration extends RecyclerView.ItemDecoration {
     if (headerHolder == null) {
 
       if (key != StickyHeaderAdapter.NO_HEADER_ID) {
-        headerHolder = adapter.onCreateHeaderViewHolder(parent  );
+        headerHolder = adapter.onCreateHeaderViewHolder(parent, position);
         //noinspection unchecked
         adapter.onBindHeaderViewHolder(headerHolder, position);
       }
@@ -221,7 +221,7 @@ public class StickyHeaderDecoration extends RecyclerView.ItemDecoration {
      * @param position position in the adapter
      * @return a view holder for the created view
      */
-    T onCreateHeaderViewHolder(ViewGroup parent);
+    T onCreateHeaderViewHolder(ViewGroup parent, int position);
 
     /**
      * Updates the header view to reflect the header data for the given position.

src/org/thoughtcrime/securesms/util/adapter/FixedViewsAdapter.java

@@ -0,0 +1,67 @@
+package org.thoughtcrime.securesms.util.adapter;
+
+import android.view.View;
+import android.view.ViewGroup;
+
+import androidx.annotation.NonNull;
+import androidx.recyclerview.widget.RecyclerView;
+
+import java.util.Arrays;
+import java.util.List;
+
+public final class FixedViewsAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
+
+  private final List<View> viewList;
+
+  private boolean hidden;
+
+  public FixedViewsAdapter(@NonNull View... viewList) {
+    this.viewList = Arrays.asList(viewList);
+  }
+
+  @Override
+  public int getItemCount() {
+    return hidden ? 0 : viewList.size();
+  }
+
+  /**
+   * @return View type is the index.
+   */
+  @Override
+  public int getItemViewType(int position) {
+    return position;
+  }
+
+  /**
+   * @param viewType The index in the list of views.
+   */
+  @Override
+  public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int viewType) {
+    return new RecyclerView.ViewHolder(viewList.get(viewType)) {
+    };
+  }
+
+  @Override
+  public void onBindViewHolder(@NonNull RecyclerView.ViewHolder viewHolder, int position) {
+  }
+
+  @Override
+  public long getItemId(int position) {
+    return position;
+  }
+
+  public void hide() {
+    setHidden(true);
+  }
+
+  public void show() {
+    setHidden(false);
+  }
+
+  private void setHidden(boolean hidden) {
+    if (this.hidden != hidden) {
+      this.hidden = hidden;
+      notifyDataSetChanged();
+    }
+  }
+}

src/org/thoughtcrime/securesms/util/adapter/RecyclerViewConcatenateAdapter.java

@@ -0,0 +1,292 @@
+/*
+ * Copyright (C) 2017 Martijn van der Woude
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Original source: https://github.com/martijnvdwoude/recycler-view-merge-adapter
+ *
+ * This file has been modified by Signal.
+ */
+
+package org.thoughtcrime.securesms.util.adapter;
+
+import android.util.LongSparseArray;
+import android.util.SparseIntArray;
+import android.view.ViewGroup;
+
+import androidx.annotation.NonNull;
+import androidx.recyclerview.widget.RecyclerView;
+
+import java.util.LinkedList;
+import java.util.List;
+
+public class RecyclerViewConcatenateAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
+
+  private final List<ChildAdapter> adapters = new LinkedList<>();
+
+  private long nextUnassignedItemId;
+
+  /**
+   * Map of global view type to local adapter.
+   * <p>
+   * Not the same as {@link #adapters}, it may have duplicates and may be in a different order.
+   */
+  private final List<ChildAdapter> viewTypes = new LinkedList<>();
+
+  /** Observes a single sub adapter and maps the positions on the events to global positions. */
+  private static class AdapterDataObserver extends RecyclerView.AdapterDataObserver {
+
+    private final RecyclerViewConcatenateAdapter                mergeAdapter;
+    private final RecyclerView.Adapter<RecyclerView.ViewHolder> adapter;
+
+    AdapterDataObserver(RecyclerViewConcatenateAdapter mergeAdapter, RecyclerView.Adapter<RecyclerView.ViewHolder> adapter) {
+      this.mergeAdapter = mergeAdapter;
+      this.adapter      = adapter;
+    }
+
+    @Override
+    public void onChanged() {
+      mergeAdapter.notifyDataSetChanged();
+    }
+
+    @Override
+    public void onItemRangeChanged(int positionStart, int itemCount) {
+      int subAdapterOffset = mergeAdapter.getSubAdapterFirstGlobalPosition(adapter);
+
+      mergeAdapter.notifyItemRangeChanged(subAdapterOffset + positionStart, itemCount);
+    }
+
+    @Override
+    public void onItemRangeInserted(int positionStart, int itemCount) {
+      int subAdapterOffset = mergeAdapter.getSubAdapterFirstGlobalPosition(adapter);
+
+      mergeAdapter.notifyItemRangeInserted(subAdapterOffset + positionStart, itemCount);
+    }
+
+    @Override
+    public void onItemRangeRemoved(int positionStart, int itemCount) {
+      int subAdapterOffset = mergeAdapter.getSubAdapterFirstGlobalPosition(adapter);
+
+      mergeAdapter.notifyItemRangeRemoved(subAdapterOffset + positionStart, itemCount);
+    }
+  }
+
+  private static class ChildAdapter {
+
+    final RecyclerView.Adapter<RecyclerView.ViewHolder> adapter;
+
+    /** Map of global view types to local view types */
+    private final SparseIntArray globalViewTypesMap = new SparseIntArray();
+
+    /** Map of local view types to global view types */
+    private final SparseIntArray localViewTypesMap = new SparseIntArray();
+
+    private final AdapterDataObserver adapterDataObserver;
+
+    /** Map of local ids to global ids. */
+    private final LongSparseArray<Long> localItemIdMap = new LongSparseArray<>();
+
+    ChildAdapter(@NonNull RecyclerView.Adapter<RecyclerView.ViewHolder> adapter, @NonNull AdapterDataObserver adapterDataObserver) {
+      this.adapter             = adapter;
+      this.adapterDataObserver = adapterDataObserver;
+
+      this.adapter.registerAdapterDataObserver(this.adapterDataObserver);
+    }
+
+    int getGlobalItemViewType(int localPosition, int defaultValue) {
+      int localViewType  = adapter.getItemViewType(localPosition);
+      int globalViewType = localViewTypesMap.get(localViewType, defaultValue);
+
+      if (globalViewType == defaultValue) {
+        globalViewTypesMap.append(globalViewType, localViewType);
+        localViewTypesMap.append(localViewType, globalViewType);
+      }
+
+      return globalViewType;
+    }
+
+    long getGlobalItemId(int localPosition, long defaultGlobalValue) {
+      final long localItemId = adapter.getItemId(localPosition);
+
+      if (RecyclerView.NO_ID == localItemId) {
+        return RecyclerView.NO_ID;
+      }
+
+      final Long globalItemId = localItemIdMap.get(localItemId);
+
+      if (globalItemId == null) {
+        localItemIdMap.put(localItemId, defaultGlobalValue);
+        return defaultGlobalValue;
+      }
+
+      return globalItemId;
+    }
+
+    void unregister() {
+      adapter.unregisterAdapterDataObserver(adapterDataObserver);
+    }
+
+    RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int globalViewType) {
+      int localViewType = globalViewTypesMap.get(globalViewType);
+
+      return adapter.onCreateViewHolder(viewGroup, localViewType);
+    }
+  }
+
+  static class ChildAdapterPositionPair {
+
+    final ChildAdapter childAdapter;
+    final int          localPosition;
+
+    ChildAdapterPositionPair(@NonNull ChildAdapter adapter, int position) {
+      childAdapter  = adapter;
+      localPosition = position;
+    }
+
+    RecyclerView.Adapter<RecyclerView.ViewHolder> getAdapter() {
+      return childAdapter.adapter;
+    }
+  }
+
+  /**
+   * @param adapter Append an adapter to the list of adapters.
+   */
+  public void addAdapter(@NonNull RecyclerView.Adapter<RecyclerView.ViewHolder> adapter) {
+    addAdapter(adapters.size(), adapter);
+  }
+
+  /**
+   * @param index   The index at which to add an adapter to the list of adapters.
+   * @param adapter The adapter to add.
+   */
+  public void addAdapter(int index, @NonNull RecyclerView.Adapter<RecyclerView.ViewHolder> adapter) {
+    AdapterDataObserver adapterDataObserver = new AdapterDataObserver(this, adapter);
+    adapters.add(index, new ChildAdapter(adapter, adapterDataObserver));
+    notifyDataSetChanged();
+  }
+
+  /**
+   * Clear all adapters from the list of adapters.
+   */
+  public void clearAdapters() {
+    for (ChildAdapter childAdapter : adapters) {
+      childAdapter.unregister();
+    }
+
+    adapters.clear();
+    notifyDataSetChanged();
+  }
+
+  /**
+   * Return a childAdapterPositionPair object for a given global position.
+   *
+   * @param globalPosition The global position in the entire set of items.
+   * @return A childAdapterPositionPair object containing a reference to the adapter and the local
+   * position in that adapter that corresponds to the given global position.
+   */
+  @NonNull
+  ChildAdapterPositionPair getLocalPosition(final int globalPosition) {
+    int count = 0;
+
+    for (ChildAdapter childAdapter : adapters) {
+      int newCount = count + childAdapter.adapter.getItemCount();
+
+      if (globalPosition < newCount) {
+        return new ChildAdapterPositionPair(childAdapter, globalPosition - count);
+      }
+
+      count = newCount;
+    }
+
+    throw new AssertionError("Position out of range");
+  }
+
+  @Override
+  @NonNull
+  public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int viewType) {
+    ChildAdapter childAdapter = viewTypes.get(viewType);
+    if (childAdapter == null) {
+      throw new AssertionError("Unknown view type");
+    }
+
+    return childAdapter.onCreateViewHolder(viewGroup, viewType);
+  }
+
+  /**
+   * Return the first global position in the entire set of items for a given adapter.
+   *
+   * @param adapter The adapter for which to the return the first global position.
+   * @return The first global position for the given adapter, or -1 if no such position could be found.
+   */
+  private int getSubAdapterFirstGlobalPosition(@NonNull RecyclerView.Adapter adapter) {
+    int count = 0;
+
+    for (ChildAdapter childAdapterWrapper : adapters) {
+      RecyclerView.Adapter childAdapter = childAdapterWrapper.adapter;
+
+      if (childAdapter == adapter) {
+        return count;
+      }
+
+      count += childAdapter.getItemCount();
+    }
+
+    throw new AssertionError("Adapter not found in list of adapters");
+  }
+
+  @Override
+  public void onBindViewHolder(@NonNull RecyclerView.ViewHolder viewHolder, int position) {
+    ChildAdapterPositionPair childAdapterPositionPair = getLocalPosition(position);
+    RecyclerView.Adapter adapter = childAdapterPositionPair.getAdapter();
+    //noinspection unchecked
+    adapter.onBindViewHolder(viewHolder, childAdapterPositionPair.localPosition);
+  }
+
+  @Override
+  public int getItemViewType(int position) {
+    int                      nextUnassignedViewType = viewTypes.size();
+    ChildAdapterPositionPair localPosition          = getLocalPosition(position);
+
+    int viewType = localPosition.childAdapter.getGlobalItemViewType(localPosition.localPosition, nextUnassignedViewType);
+
+    if (viewType == nextUnassignedViewType) {
+      viewTypes.add(viewType, localPosition.childAdapter);
+    }
+
+    return viewType;
+  }
+
+  @Override
+  public long getItemId(int position) {
+    ChildAdapterPositionPair localPosition = getLocalPosition(position);
+
+    long itemId = localPosition.childAdapter.getGlobalItemId(localPosition.localPosition, nextUnassignedItemId);
+
+    if (itemId == nextUnassignedItemId) {
+      nextUnassignedItemId++;
+    }
+
+    return itemId;
+  }
+
+  @Override
+  public int getItemCount() {
+    int count = 0;
+
+    for (ChildAdapter adapter : adapters) {
+      count += adapter.adapter.getItemCount();
+    }
+
+    return count;
+  }
+}

src/org/thoughtcrime/securesms/util/adapter/RecyclerViewConcatenateAdapterStickyHeader.java

@@ -0,0 +1,61 @@
+package org.thoughtcrime.securesms.util.adapter;
+
+import android.view.ViewGroup;
+
+import androidx.recyclerview.widget.RecyclerView;
+
+import org.thoughtcrime.securesms.components.RecyclerViewFastScroller;
+import org.thoughtcrime.securesms.util.StickyHeaderDecoration;
+import org.whispersystems.libsignal.util.Pair;
+import org.whispersystems.libsignal.util.guava.Optional;
+
+public final class RecyclerViewConcatenateAdapterStickyHeader extends    RecyclerViewConcatenateAdapter
+                                                              implements StickyHeaderDecoration.StickyHeaderAdapter,
+                                                                         RecyclerViewFastScroller.FastScrollAdapter
+{
+
+  @Override
+  public long getHeaderId(int position) {
+    return getForPosition(position).transform(p -> p.first().getHeaderId(p.second())).or(-1L);
+  }
+
+  @Override
+  public RecyclerView.ViewHolder onCreateHeaderViewHolder(ViewGroup parent, int position) {
+    return getForPosition(position).transform(p -> p.first().onCreateHeaderViewHolder(parent, p.second())).orNull();
+  }
+
+  @Override
+  public void onBindHeaderViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
+    Optional<Pair<StickyHeaderDecoration.StickyHeaderAdapter, Integer>> forPosition = getForPosition(position);
+
+    if (forPosition.isPresent()) {
+      Pair<StickyHeaderDecoration.StickyHeaderAdapter, Integer> stickyHeaderAdapterIntegerPair = forPosition.get();
+      //noinspection unchecked
+      stickyHeaderAdapterIntegerPair.first().onBindHeaderViewHolder(viewHolder, stickyHeaderAdapterIntegerPair.second());
+    }
+  }
+
+  @Override
+  public CharSequence getBubbleText(int position) {
+    Optional<Pair<StickyHeaderDecoration.StickyHeaderAdapter, Integer>> forPosition = getForPosition(position);
+
+    return forPosition.transform(a -> {
+      if (a.first() instanceof RecyclerViewFastScroller.FastScrollAdapter) {
+        return ((RecyclerViewFastScroller.FastScrollAdapter) a.first()).getBubbleText(a.second());
+      } else {
+        return "";
+      }
+    }).or("");
+  }
+
+  private Optional<Pair<StickyHeaderDecoration.StickyHeaderAdapter, Integer>> getForPosition(int position) {
+    ChildAdapterPositionPair                                localAdapterPosition = getLocalPosition(position);
+    RecyclerView.Adapter<? extends RecyclerView.ViewHolder> adapter              = localAdapterPosition.getAdapter();
+
+    if (adapter instanceof StickyHeaderDecoration.StickyHeaderAdapter) {
+      StickyHeaderDecoration.StickyHeaderAdapter sticky = (StickyHeaderDecoration.StickyHeaderAdapter) adapter;
+      return Optional.of(new Pair<>(sticky, localAdapterPosition.localPosition));
+    }
+    return Optional.absent();
+  }
+}