GWT ToggleButton ActionCell

GWT with version 2.1 introduced Cell widgets, we can find CellList, CellTable, CellTree and CellBrowser and a lot of Cell Types : TextCell,EditTextCell, ButtonCell ... GWT Developerr's Guide, what I wasn't able to find is a ToggleButton Cell Type so I decided to implement my own version.

I called it ToggleButtonActionCell and the following is the code I wrote:


public class ToggleButtonActionCell<C> extends AbstractCell<C> {

private SelectionModel<C> selectionModel;

/**
* An html string representation of a pressed button.
*/
private static final SafeHtml TOGGLE_BUTTON_UP = SafeHtmlUtils
.fromSafeConstant("<button type=\"button\" class=\"toggleButton toggleButton-up\"        tabindex=\"-1\" aria-pressed=\"true\">");

/**
* An html string representation of an unpressed.
*/
private static final SafeHtml TOGGLE_BUTTON_DOWN = SafeHtmlUtils
.fromSafeConstant("<button type=\"button\" class=\"toggleButton toggleButton-down\" tabindex=\"-1\" aria-pressed=\"false\">");

/**
* The delegate that will handle events from the cell.
*
* @param <T>
*            the type that this delegate acts on
*/
public static interface Delegate<T> {
/**
* Perform the desired action on the given object.
*
* @param object
*            the object to be acted upon
*/
void execute(T object, Boolean wasPressed);
}

private final SafeHtml upImage;
private final SafeHtml downImage;

protected final SafeHtml htmlPressed;
protected final SafeHtml htmlUnPpressed;

private final Delegate<C> delegate;

SafeHtmlBuilder sb;

public ToggleButtonActionCell(Image upImage, Image downImage,
SelectionModel<C> selectionModel, Delegate<C> delegate) {
super("click");
this.upImage = new SafeHtmlBuilder().appendHtmlConstant(
upImage.toString()).toSafeHtml();
this.downImage = new SafeHtmlBuilder().appendHtmlConstant(
downImage.toString()).toSafeHtml();
this.delegate = delegate;
this.htmlPressed = new SafeHtmlBuilder().append(TOGGLE_BUTTON_UP)
.append(this.downImage).appendHtmlConstant("</button>")
.toSafeHtml();
this.htmlUnPpressed = new SafeHtmlBuilder().append(TOGGLE_BUTTON_DOWN)
.append(this.upImage).appendHtmlConstant("</button>")
.toSafeHtml();
this.selectionModel = selectionModel;
}

@Override
public void render(Context context, C value, SafeHtmlBuilder sb) {
this.sb = sb;
if (selectionModel.isSelected(value)) {
sb.append(htmlPressed);
} else {
sb.append(htmlUnPpressed);
}
}

@Override
public void onBrowserEvent(Context context, Element parent, C value,
NativeEvent event, ValueUpdater<C> valueUpdater) {

if ("click".equals(event.getType())) {
super.onBrowserEvent(context, parent, value, event, valueUpdater);
onEnterKeyDown(context, parent, value, event, valueUpdater);
selectionModel.setSelected(value, !selectionModel.isSelected(value));
toggleButtonImage(parent, context,selectionModel.isSelected(value));
}
}

@Override
protected void onEnterKeyDown(Context context, Element parent, C value,
NativeEvent event, ValueUpdater<C> valueUpdater) {
delegate.execute(value, selectionModel.isSelected(value));
}

private void toggleButtonImage(Element parent, Context context, Boolean setPressed) {
com.google.gwt.user.client.Element button = getButton(parent);

if (setPressed) {
setPressed(button, true);
setButtonImage(button, downImage);
} else {
setPressed(button, false);
setButtonImage(button, upImage);
}
}

private void setPressed(com.google.gwt.user.client.Element button, boolean isPressed) {
DOM.setElementAttribute(button, "aria-pressed", Boolean.toString(isPressed));
if(isPressed){
DOM.setElementAttribute(button, "class", "toggleButton toggleButton-down");
}else{
DOM.setElementAttribute(button, "class", "toggleButton toggleButton-up");
}
}

private void setButtonImage(Element button, SafeHtml image) {
Element img = button.getFirstChildElement();
button.removeChild(img);
button.setInnerHTML(image.asString());
}

private com.google.gwt.user.client.Element getButton(Element parent) {
com.google.gwt.user.client.Element button = parent
.getFirstChildElement().cast();
return button;
}
}

I hope someone can find this code useful and any comment and suggestion is welcome.