1 files changed, 112 insertions, 0 deletions
diff --git a/core/java/android/content/AbstractCursorEntityIterator.java b/core/java/android/content/AbstractCursorEntityIterator.java
new file mode 100644
index 0000000..bf3c4de
--- /dev/null
+++ b/core/java/android/content/AbstractCursorEntityIterator.java
@@ -0,0 +1,112 @@
+package android.content;
+
+import android.database.Cursor;
+import android.database.sqlite.SQLiteDatabase;
+import android.os.RemoteException;
+
+/**
+ * An abstract class that makes it easy to implement an EntityIterator over a cursor.
+ * The user must implement {@link #newEntityFromCursorLocked}, which runs inside of a
+ * database transaction.
+ */
+public abstract class AbstractCursorEntityIterator implements EntityIterator {
+    private final Cursor mEntityCursor;
+    private final SQLiteDatabase mDb;
+    private volatile Entity mNextEntity;
+    private volatile boolean mIsClosed;
+
+    public AbstractCursorEntityIterator(SQLiteDatabase db, Cursor entityCursor) {
+        mEntityCursor = entityCursor;
+        mDb = db;
+        mNextEntity = null;
+        mIsClosed = false;
+    }
+
+    /**
+     * If there are entries left in the cursor then advance the cursor and use the new row to
+     * populate mNextEntity. If the cursor is at the end or if advancing it causes the cursor
+     * to become at the end then set mEntityCursor to null. If newEntityFromCursor returns null
+     * then continue advancing until it either returns a non-null Entity or the cursor reaches
+     * the end.
+     */
+    private void fillEntityIfAvailable() {
+        while (mNextEntity == null) {
+            if (!mEntityCursor.moveToNext()) {
+                // the cursor is at then end, bail out
+                return;
+            }
+            // This may return null if newEntityFromCursor is not able to create an entity
+            // from the current cursor position. In that case this method will loop and try
+            // the next cursor position
+            mNextEntity = newEntityFromCursorLocked(mEntityCursor);
+        }
+        mDb.beginTransaction();
+        try {
+            int position = mEntityCursor.getPosition();
+            mNextEntity = newEntityFromCursorLocked(mEntityCursor);
+            int newPosition = mEntityCursor.getPosition();
+            if (newPosition != position) {
+                throw new IllegalStateException("the cursor position changed during the call to"
+                        + "newEntityFromCursorLocked, from " + position + " to " + newPosition);
+            }
+        } finally {
+            mDb.endTransaction();
+        }
+    }
+
+    /**
+     * Checks if there are more Entities accessible via this iterator. This may not be called
+     * if the iterator is already closed.
+     * @return true if the call to next() will return an Entity.
+     */
+    public boolean hasNext() {
+        if (mIsClosed) {
+            throw new IllegalStateException("calling hasNext() when the iterator is closed");
+        }
+        fillEntityIfAvailable();
+        return mNextEntity != null;
+    }
+
+    /**
+     * Returns the next Entity that is accessible via this iterator. This may not be called
+     * if the iterator is already closed.
+     * @return the next Entity that is accessible via this iterator
+     */
+    public Entity next() {
+        if (mIsClosed) {
+            throw new IllegalStateException("calling next() when the iterator is closed");
+        }
+        if (!hasNext()) {
+            throw new IllegalStateException("you may only call next() if hasNext() is true");
+        }
+
+        try {
+            return mNextEntity;
+        } finally {
+            mNextEntity = null;
+        }
+    }
+
+    /**
+     * Closes this iterator making it invalid. If is invalid for the user to call any public
+     * method on the iterator once it has been closed.
+     */
+    public void close() {
+        if (mIsClosed) {
+            throw new IllegalStateException("closing when already closed");
+        }
+        mIsClosed = true;
+        mEntityCursor.close();
+    }
+
+    /**
+     * Returns a new Entity from the current cursor position. This is called from within a
+     * database transaction. If a new entity cannot be created from this cursor position (e.g.
+     * if the row that is referred to no longer exists) then this may return null. The cursor
+     * is guaranteed to be pointing to a valid row when this call is made. The implementation
+     * of newEntityFromCursorLocked is not allowed to change the position of the cursor.
+     * @param cursor from where to read the data for the Entity
+     * @return an Entity that corresponds to the current cursor position or null
+     */
+    public abstract Entity newEntityFromCursorLocked(Cursor cursor);
+}