Make ListView's illegal state exception more helpful

Change-Id: I3d3205d32c6992c184a218248ba72ebf6c45a2d1
diff --git a/core/java/android/widget/ListView.java b/core/java/android/widget/ListView.java
index 389d9d6..b239fbd 100644
--- a/core/java/android/widget/ListView.java
+++ b/core/java/android/widget/ListView.java
@@ -1555,8 +1555,9 @@
             } else if (mItemCount != mAdapter.getCount()) {
                 throw new IllegalStateException("The content of the adapter has changed but "
                         + "ListView did not receive a notification. Make sure the content of "
-                        + "your adapter is not modified from a background thread, but only "
-                        + "from the UI thread. [in ListView(" + getId() + ", " + getClass() 
+                        + "your adapter is not modified from a background thread, but only from "
+                        + "the UI thread. Make sure your adapter calls notifyDataSetChanged() "
+                        + "when its content changes. [in ListView(" + getId() + ", " + getClass()
                         + ") with Adapter(" + mAdapter.getClass() + ")]");
             }