Dynamic grid creation

<zk>			
	<window apply="ctrl.MyComposer">
		<button id="btn1" label="2"/>
		<button id="btn2" label="4"/>
		<button id="btn3" label="6"/>
		<grid id="grid">
			<columns/>
		</grid>
	</window>
</zk>

package ctrl;

import java.util.*;

import org.zkoss.zk.ui.Component;
import org.zkoss.zk.ui.Executions;
import org.zkoss.zk.ui.event.Event;
import org.zkoss.zk.ui.event.EventListener;
import org.zkoss.zk.ui.util.GenericForwardComposer;
import org.zkoss.zul.*;

public class MyComposer extends GenericForwardComposer {

	private Button btn1, btn2, btn3;
	private Grid grid;	
	private ListModelList lmList;
	
	@Override
	public void doAfterCompose(Component comp) throws Exception {
		super.doAfterCompose(comp);
		
		grid.setRowRenderer(new RowRenderer() {			
			public void render(Row row, Object data) throws Exception {
				if (data == null) return;
				
				Columns columns = row.getGrid().getColumns();
				if (columns.getChildren() == null) return;
				
				int colCount = columns.getChildren().size();
				
				Map<String, Object> params = new HashMap<String, Object>();
				params.put("items", createStringList(colCount, String.valueOf(data)));
				row.appendChild(Executions.createComponents("items.zul", row, params));
			}
		});				
		
		lmList = new ListModelList();
		grid.setModel(lmList);
		
		
		EventListener onClickEvt = new EventListener() {			
			public void onEvent(Event event) throws Exception {
				
				Columns columns = grid.getColumns();
				if (columns.getChildren() == null) return;
				
				columns.detach();
				
				Button btn = (Button) event.getTarget();
				int num = Integer.parseInt(btn.getLabel());
				
				Map<String, Object> params = new HashMap<String, Object>();
				params.put("columns", createStringList(num, "column"));				
				grid.appendChild(Executions.createComponents("columns.zul", grid, params));
				
				lmList.clear();
				lmList.addAll(createStringList(num, "item"));
			}
		};
		
		btn1.addEventListener("onClick", onClickEvt);
		btn2.addEventListener("onClick", onClickEvt);
		btn3.addEventListener("onClick", onClickEvt);
		
	}
	private List<String> createStringList(int num, String startWith){
		List<String> result = new ArrayList<String>();
		
		for (int i = 0; i < num; i++) {
			result.add(startWith + (i + 1));
		}
		return result;
	}
}

<columns>
	<column forEach="${arg.columns}" label="${each}" />
</columns>

<label forEach="${arg.items}" value="${each}" />

for (int i = 0; i < colCount; i++) {
    row.appendChild(new Label(String.valueOf(data)));
}