vaadin-framework/src/com/itmill/toolkit/demo/colorpicker/gwt/client/ui/ItkColorPicker.java

package com.itmill.toolkit.demo.colorpicker.gwt.client.ui;

import com.itmill.toolkit.terminal.gwt.client.ApplicationConnection;
import com.itmill.toolkit.terminal.gwt.client.Paintable;
import com.itmill.toolkit.terminal.gwt.client.UIDL;

public class ItkColorPicker extends GwtColorPicker implements Paintable {

	/** Set the CSS class name to allow styling. */
	public static final String CLASSNAME = "example-colorpicker";

	/** Component identifier in UIDL communications. */
	String uidl_id;

	/** Reference to the server connection object. */
	ApplicationConnection client;

	/**
	 * The constructor should first call super() to initialize the component and
	 * then handle any initialization relevant to IT Mill Toolkit.
	 */
	public ItkColorPicker() {
		// The superclass has a lot of relevant initialization
		super();

		// This method call of the Paintable interface sets the component
		// style name in DOM tree
		setStyleName(CLASSNAME);
	}

	/**
	 * This method must be implemented to update the client-side component from
	 * UIDL data received from server.
	 * 
	 * This method is called when the page is loaded for the first time, and
	 * every time UI changes in the component are received from the server.
	 */
	public void updateFromUIDL(UIDL uidl, ApplicationConnection client) {
		// This call should be made first. Ensure correct implementation,
		// but don't let container manage caption etc.
		if (client.updateComponent(this, uidl, false))
			return;

		// Save reference to server connection object to be able to send
		// user interaction later
		this.client = client;

		// Save the UIDL identifier for the component
		uidl_id = uidl.getId();

		// Get value received from server and actualize it in the GWT component
		setColor(uidl.getStringVariable("colorname"));
	}

	/** Override the method to communicate the new value to server. */
	public void setColor(String newcolor) {
		// Ignore if no change
		if (newcolor.equals(currentcolor.getText()))
			return;

		// Let the original implementation to do whatever it needs to do
		super.setColor(newcolor);

		// Updating the state to the server can not be done before
		// the server connection is known, i.e., before updateFromUIDL()
		// has been called.
		if (uidl_id == null || client == null)
			return;

		// Communicate the user interaction parameters to server. This call will
		// initiate an AJAX request to the server.
		client.updateVariable(uidl_id, "colorname", newcolor, true);
	}
}