private void setContentProvider() {
IPreferenceStore preferenceStore= DroolsEclipsePlugin.getDefault().getPreferenceStore();
groupByRulegroup = preferenceStore.getBoolean("GroupByRuleGroupAction.isChecked");
contentProvider = new DroolsContentProvider();
groupByRuleGroupContentProvider = new DroolsGroupByRuleGroupContentProvider();
if (groupByRulegroup) {
viewer.setContentProvider(groupByRuleGroupContentProvider);
} else {
viewer.setContentProvider(contentProvider);