Fixed a bug and added another test that verifies it.

Author: CodingDoug

database/src/androidTest/java/com/firebase/ui/database/FirebaseArrayTest.java

@@ -112,7 +112,7 @@ public Boolean call() throws Exception {
     }
 
     @Test
-    public void testChangePriorities() throws Exception {
+    public void testChangePriorityBackToFront() throws Exception {
         runAndWaitUntil(mArray, new Runnable() {
             public void run() {
                 mArray.getItem(2).getRef().setPriority(0.5);
@@ -123,4 +123,17 @@ public Boolean call() throws Exception {
             }
         });
     }
+
+    @Test
+    public void testChangePriorityFrontToBack() throws Exception {
+        runAndWaitUntil(mArray, new Runnable() {
+            public void run() {
+                mArray.getItem(0).getRef().setPriority(4);
+            }
+        }, new Callable<Boolean>() {
+            public Boolean call() throws Exception {
+                return isValuesEqual(mArray, new int[]{2, 3, 1});
+            }
+        });
+    }
 }

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

@@ -22,6 +22,7 @@
 
 import java.util.ArrayList;
 import java.util.HashMap;
+import java.util.ListIterator;
 
 /**
  * This class implements an array-like collection on top of a Firebase location.
@@ -71,6 +72,16 @@ public int getIndexForKey(String key) {
         }
     }
 
+    private int scanArrayForKey(String key) {
+        final ListIterator<DataSnapshot> it = mSnapshots.listIterator();
+        while (it.hasNext()) {
+            if (it.next().getKey().equals(key)) {
+                return it.previousIndex();
+            }
+        }
+        throw new IllegalArgumentException("Key not found");
+    }
+
     @Override
     public void onChildAdded(DataSnapshot snapshot, String previousChildKey) {
         int index = 0;
@@ -101,9 +112,15 @@ public void onChildRemoved(DataSnapshot snapshot) {
     public void onChildMoved(DataSnapshot snapshot, String previousChildKey) {
         int oldIndex = getIndexForKey(snapshot.getKey());
         mSnapshots.remove(oldIndex);
-        int newIndex = previousChildKey == null ? 0 : (getIndexForKey(previousChildKey) + 1);
+        int newIndex = previousChildKey == null ? 0 : (scanArrayForKey(previousChildKey) + 1);
         mSnapshots.add(newIndex, snapshot);
-        mSnapshotMap.put(snapshot.getKey(), newIndex);
+
+        // Rebuild the map of indices
+        mSnapshotMap.clear();
+        for (int i = 0; i < mSnapshots.size(); i++) {
+            mSnapshotMap.put(mSnapshots.get(i).getKey(), i);
+        }
+
         notifyChangedListeners(OnChangedListener.EventType.MOVED, newIndex, oldIndex);
     }