This change allows easy detection of the list being empty *and* respo… (#487)

Author: puf

app/src/main/java/com/firebase/uidemo/database/ChatActivity.java

@@ -51,13 +51,15 @@ public class ChatActivity extends AppCompatActivity implements FirebaseAuth.Auth
     private static final String TAG = "RecyclerViewDemo";
 
     private FirebaseAuth mAuth;
+    private DatabaseReference mRef;
     private DatabaseReference mChatRef;
     private Button mSendButton;
     private EditText mMessageEdit;
 
     private RecyclerView mMessages;
     private LinearLayoutManager mManager;
     private FirebaseRecyclerAdapter<Chat, ChatHolder> mRecyclerViewAdapter;
+    private View mEmptyListView;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
@@ -70,7 +72,10 @@ protected void onCreate(Bundle savedInstanceState) {
         mSendButton = (Button) findViewById(R.id.sendButton);
         mMessageEdit = (EditText) findViewById(R.id.messageEdit);
 
-        mChatRef = FirebaseDatabase.getInstance().getReference().child("chats");
+        mEmptyListView = findViewById(R.id.emptyTextView);
+
+        mRef = FirebaseDatabase.getInstance().getReference();
+        mChatRef = mRef.child("chats");
 
         mSendButton.setOnClickListener(new View.OnClickListener() {
             @Override
@@ -153,6 +158,12 @@ public void populateViewHolder(ChatHolder chatView, Chat chat, int position) {
                     chatView.setIsSender(false);
                 }
             }
+
+            @Override
+            protected void onDataChanged() {
+                // if there are no chat messages, show a view that invites the user to add a message
+                mEmptyListView.setVisibility(mRecyclerViewAdapter.getItemCount() == 0 ? View.VISIBLE : View.INVISIBLE);
+            }
         };
 
         // Scroll to bottom on new messages

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

@@ -6,6 +6,13 @@
     android:layout_height="match_parent"
     tools:context=".database.ChatActivity">
 
+    <TextView
+        android:id="@+id/emptyTextView"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:text="@string/start_chatting"
+        android:padding="16dp" />
+
     <android.support.v7.widget.RecyclerView
         android:id="@+id/messagesList"
         android:layout_width="match_parent"

app/src/main/res/values/strings.xml

@@ -64,4 +64,7 @@
     <string name="choose_image">Choose Image</string>
     <string name="accessibility_downloaded_image">Downloaded image</string>
     <string name="drive_file">Drive File</string>
+
+    <!-- strings for Auth UI demo activities -->
+    <string name="start_chatting">No messages. Start chatting at the bottom!</string>
 </resources>

database/src/main/java/com/firebase/ui/database/FirebaseArray.java

@@ -18,20 +18,24 @@
 import com.google.firebase.database.DataSnapshot;
 import com.google.firebase.database.DatabaseError;
 import com.google.firebase.database.Query;
+import com.google.firebase.database.ValueEventListener;
 
 import java.util.ArrayList;
 import java.util.List;
 
 /**
  * This class implements an array-like collection on top of a Firebase location.
  */
-class FirebaseArray implements ChildEventListener {
+class FirebaseArray implements ChildEventListener, ValueEventListener {
     public interface OnChangedListener {
         enum EventType {ADDED, CHANGED, REMOVED, MOVED}
 
-        void onChanged(EventType type, int index, int oldIndex);
+        void onChildChanged(EventType type, int index, int oldIndex);
+
+        void onDataChanged();
 
         void onCancelled(DatabaseError databaseError);
+
     }
 
     private Query mQuery;
@@ -41,10 +45,12 @@ enum EventType {ADDED, CHANGED, REMOVED, MOVED}
     public FirebaseArray(Query ref) {
         mQuery = ref;
         mQuery.addChildEventListener(this);
+        mQuery.addValueEventListener(this);
     }
 
     public void cleanup() {
-        mQuery.removeEventListener(this);
+        mQuery.removeEventListener((ValueEventListener) this);
+        mQuery.removeEventListener((ChildEventListener) this);
     }
 
     public int getCount() {
@@ -100,6 +106,11 @@ public void onChildMoved(DataSnapshot snapshot, String previousChildKey) {
         notifyChangedListeners(OnChangedListener.EventType.MOVED, newIndex, oldIndex);
     }
 
+    @Override
+    public void onDataChange(DataSnapshot dataSnapshot) {
+        mListener.onDataChanged();
+    }
+
     @Override
     public void onCancelled(DatabaseError error) {
         notifyCancelledListeners(error);
@@ -115,7 +126,7 @@ protected void notifyChangedListeners(OnChangedListener.EventType type, int inde
 
     protected void notifyChangedListeners(OnChangedListener.EventType type, int index, int oldIndex) {
         if (mListener != null) {
-            mListener.onChanged(type, index, oldIndex);
+            mListener.onChildChanged(type, index, oldIndex);
         }
     }
 

database/src/main/java/com/firebase/ui/database/FirebaseListAdapter.java

@@ -69,17 +69,34 @@ public abstract class FirebaseListAdapter<T> extends BaseAdapter {
 
         mSnapshots.setOnChangedListener(new FirebaseArray.OnChangedListener() {
             @Override
-            public void onChanged(EventType type, int index, int oldIndex) {
+            public void onChildChanged(EventType type, int index, int oldIndex) {
                 notifyDataSetChanged();
             }
 
             @Override
             public void onCancelled(DatabaseError databaseError) {
                 FirebaseListAdapter.this.onCancelled(databaseError);
             }
+
+            @Override
+            public void onDataChanged() {
+                FirebaseListAdapter.this.onDataChanged();
+            }
         });
     }
 
+
+    /* This method will be triggered each time updates from the database have been completely processed.
+     * So the first time this method is called, the initial data has been loaded - including the case
+     * when no data at all is available. Each next time the method is called, a complete update (potentially
+     * consisting of updates to multiple child items) has been completed.
+     * <p>
+     * You would typically override this method to hide a loading indicator (after the initial load) or
+     * to complete a batch update to a UI element.
+     */
+    protected void onDataChanged() {
+    }
+
     /**
      * @param activity    The activity containing the ListView
      * @param modelClass  Firebase will marshall the data at a location into

database/src/main/java/com/firebase/ui/database/FirebaseRecyclerAdapter.java

@@ -91,7 +91,7 @@ public abstract class FirebaseRecyclerAdapter<T, VH extends RecyclerView.ViewHol
 
         mSnapshots.setOnChangedListener(new FirebaseArray.OnChangedListener() {
             @Override
-            public void onChanged(EventType type, int index, int oldIndex) {
+            public void onChildChanged(EventType type, int index, int oldIndex) {
                 switch (type) {
                     case ADDED:
                         notifyItemInserted(index);
@@ -114,9 +114,25 @@ public void onChanged(EventType type, int index, int oldIndex) {
             public void onCancelled(DatabaseError databaseError) {
                 FirebaseRecyclerAdapter.this.onCancelled(databaseError);
             }
+
+            @Override
+            public void onDataChanged() {
+                FirebaseRecyclerAdapter.this.onDataChanged();
+            }
         });
     }
 
+    /* This method will be triggered each time updates from the database have been completely processed.
+     * So the first time this method is called, the initial data has been loaded - including the case
+     * when no data at all is available. Each next time the method is called, a complete update (potentially
+     * consisting of updates to multiple child items) has been completed.
+     * <p>
+     * You would typically override this method to hide a loading indicator (after the initial load) or
+     * to complete a batch update to a UI element.
+     */
+    protected void onDataChanged() {
+    }
+
     /**
      * @param modelClass      Firebase will marshall the data at a location into
      *                        an instance of a class that you provide