final Display display = findDisplay();
display.asyncExec(new Runnable(){
public void run() {
MapGraphicChooserDialog dialog = new MapGraphicChooserDialog(display
.getActiveShell(), false);
dialog.open();
if (dialog.getSelectedResources().isEmpty()) {
layer = NULL;
} else {
IGeoResource resource = dialog.getSelectedResources().get(0);
setMapGraphic((MapGraphicResource) resource);