+ public String move(int x, int y) {
+ return null;
+ }
+
+ /**
+ * Return the number of items in this {@link MainContent}, or -1 if this
+ * {@link MainContent} is not countable.
+ *
+ * @return -1 or the number of present items
+ */
+ public int getCount() {
+ return -1;
+ }
+
+ /**
+ * Refresh the display according to the actual data (this method should be
+ * called when the data changed).
+ */
+ public void refreshData() {
+ invalidate();
+ }