// for sync with source view.
_viewer.addDropTargetListener(new LocalSelectionDropTargetListener(
_viewer));
_viewer.addDropTargetListener(new PDTemplateTransferDropTargetListener(
_viewer));
_viewer.addDropTargetListener(new ResouceDropTargetListener(_viewer));
// add double click support.
_viewer.getControl().addMouseListener(new MouseAdapter() {