GWT ClickableCheckboxCell

import com.google.gwt.cell.client.AbstractEditableCell;
import com.google.gwt.cell.client.Cell;
import com.google.gwt.cell.client.ValueUpdater;
import com.google.gwt.dom.client.BrowserEvents;
import com.google.gwt.dom.client.Element;
import com.google.gwt.dom.client.InputElement;
import com.google.gwt.dom.client.NativeEvent;
import com.google.gwt.event.dom.client.KeyCodes;
import com.google.gwt.safehtml.shared.SafeHtml;
import com.google.gwt.safehtml.shared.SafeHtmlBuilder;
import com.google.gwt.safehtml.shared.SafeHtmlUtils;

/**
 * Original: {@link com.google.gwt.cell.client.CheckboxCell CheckboxCell}.<br>
 * A {@link Cell} used to render a checkbox. The value of the checkbox may be
 * toggled using the ENTER key as well as via mouse click.
 */
public class ClickableCheckboxCell extends AbstractEditableCell<Boolean, Boolean> {

    /**
     * An html string representation of a checked input box.
     */
    private static final SafeHtml INPUT_CHECKED = SafeHtmlUtils.fromSafeConstant("<input type=\"checkbox\" tabindex=\"-1\" checked/>");

    /**
     * An html string representation of an unchecked input box.
     */
    private static final SafeHtml INPUT_UNCHECKED = SafeHtmlUtils.fromSafeConstant("<input type=\"checkbox\" tabindex=\"-1\"/>");

    private final boolean dependsOnSelection;
    private final boolean handlesSelection;

    /**
     * Construct a new {@link com.google.gwt.cell.client.CheckboxCell} that optionally controls selection.
     *
     * @param dependsOnSelection true if the cell depends on the selection state
     * @param handlesSelection true if the cell modifies the selection state
     */
    public ClickableCheckboxCell(boolean dependsOnSelection, boolean handlesSelection) {
        super(BrowserEvents.CHANGE, BrowserEvents.KEYDOWN, BrowserEvents.CLICK);
        this.dependsOnSelection = dependsOnSelection;
        this.handlesSelection = handlesSelection;
    }

    @Override
    public boolean dependsOnSelection() {
        return dependsOnSelection;
    }

    @Override
    public boolean handlesSelection() {
        return handlesSelection;
    }

    @Override
    public boolean isEditing(Context context, Element parent, Boolean value) {
        // A checkbox is never in "edit mode". There is no intermediate state
        // between checked and unchecked.
        return false;
    }

    @Override
    public void onBrowserEvent(Context context, Element parent, Boolean value,
                               NativeEvent event, ValueUpdater<Boolean> valueUpdater) {
        String type = event.getType();

        boolean enterPressed = BrowserEvents.KEYDOWN.equals(type)
                && event.getKeyCode() == KeyCodes.KEY_ENTER;
        if (BrowserEvents.CHANGE.equals(type) || enterPressed) {
            InputElement input = parent.getFirstChild().cast();
            Boolean isChecked = input.isChecked();

            /*
             * Toggle the value if the enter key was pressed and the cell handles
             * selection or doesn't depend on selection. If the cell depends on
             * selection but doesn't handle selection, then ignore the enter key and
             * let the SelectionEventManager determine which keys will trigger a
             * change.
             */
            if (enterPressed && (handlesSelection() || !dependsOnSelection())) {
                isChecked = !isChecked;
                input.setChecked(isChecked);
            }

            /*
             * Save the new value. However, if the cell depends on the selection, then
             * do not save the value because we can get into an inconsistent state.
             */
            if (value != isChecked && !dependsOnSelection()) {
                setViewData(context.getKey(), isChecked);
            } else {
                clearViewData(context.getKey());
            }

            if (valueUpdater != null) {
                valueUpdater.update(isChecked);
            }
        }
    }

    @Override
    public void render(Context context, Boolean value, SafeHtmlBuilder sb) {
        // Get the view data.
        Object key = context.getKey();
        Boolean viewData = getViewData(key);
        if (viewData != null && viewData.equals(value)) {
            clearViewData(key);
            viewData = null;
        }

        if (value != null && ((viewData != null) ? viewData : value)) {
            sb.append(INPUT_CHECKED);
        } else {
            sb.append(INPUT_UNCHECKED);
        }
    }
}