Handle final page

Change-Id: I7e3ca99bc9f682e7989a40155b7bbd3437b98559

Author: samtstern

app/src/main/java/com/firebase/uidemo/database/firestore/FirestorePagingActivity.java

@@ -99,6 +99,10 @@ protected void onLoadingStateChanged(@NonNull LoadingState state) {
                             case LOADED:
                                 mProgressBar.setVisibility(View.GONE);
                                 break;
+                            case FINISHED:
+                                mProgressBar.setVisibility(View.GONE);
+                                showToast("Reached end of data set,");
+                                break;
                             case ERROR:
                                 showToast("An error occurred.");
                                 retry();

firestore/src/main/java/com/firebase/ui/firestore/paging/FirestoreDataSource.java

@@ -180,6 +180,13 @@ private abstract class OnLoadSuccessListener implements OnSuccessListener<QueryS
         public void onSuccess(QuerySnapshot snapshot) {
             setResult(snapshot);
             mLoadingState.postValue(LoadingState.LOADED);
+
+            // Post the 'FINISHED' state when no more pages will be loaded. The data source
+            // callbacks interpret and empty result list as a signal to cancel any future loads
+            if (snapshot.getDocuments().isEmpty()) {
+                mLoadingState.postValue(LoadingState.FINISHED);
+            }
+
             mRetryRunnable = null;
         }
 

firestore/src/main/java/com/firebase/ui/firestore/paging/LoadingState.java

@@ -19,6 +19,11 @@ public enum LoadingState {
      */
     LOADED,
 
+    /**
+     * The last page loaded had zero documents, and therefore no further pages will be loaded.
+     */
+    FINISHED,
+
     /**
      * The most recent load encountered an error.
      */