Pithos_GSS » GSS

package gr.ebs.gss.client.components;

import com.google.gwt.event.dom.client.ClickEvent;

import com.google.gwt.event.dom.client.ClickHandler;

import com.google.gwt.event.logical.shared.ValueChangeEvent;

import com.google.gwt.event.logical.shared.ValueChangeHandler;

import com.google.gwt.event.shared.HandlerRegistration;

import com.google.gwt.user.client.DOM;

import com.google.gwt.user.client.Element;

import com.google.gwt.user.client.ui.FocusWidget;

import com.google.gwt.user.client.ui.HasValue;

/**

 * Checkbox with three states (checked, unchecked and undefined).

 *

 */

public class TristateCheckBox extends FocusWidget implements HasValue<Boolean> {

    private static final String UNCHECKED_IMG = "images/tristate_unchecked.gif";

    private static final String UNKNOWN_IMG = "images/tristate_intermediate.gif";

    private static final String CHECKED_IMG = "images/tristate_checked.gif";

    private final Element buttonElement = DOM.createElement("input");

    private boolean valueChangeHandlerInitialized;

    private Boolean value;

    private Boolean initialValue;

    public TristateCheckBox(final Boolean state) {

        DOM.setElementProperty(buttonElement, "type", "image");

        setElement(buttonElement);

        setStyleName("tristateCheckbox");

        DOM.setElementAttribute(buttonElement, "src", UNCHECKED_IMG);

        addClickHandler(new ClickHandler() {

                        @Override

                        public void onClick(ClickEvent event) {

                final String img = DOM.getElementAttribute(buttonElement, "src");

                String newImg;

                if (img.endsWith(UNCHECKED_IMG))

                                        newImg = CHECKED_IMG;

                                else if (img.endsWith(UNKNOWN_IMG))

                                        newImg = UNCHECKED_IMG;

                                else if (img.endsWith(CHECKED_IMG))

                                        if (initialValue==null) // Only show unknown choice if there is a reason for it

                                                newImg = UNKNOWN_IMG;

                                        else

                                                newImg = UNCHECKED_IMG;

                                else

                                        throw new IllegalArgumentException("unknown checkbox state");

                DOM.setElementAttribute(buttonElement, "src", newImg);

            }

        });

        setState(state);

        initialValue = state;

    }

    public void setState(final Boolean state) {

            DOM.setElementAttribute(buttonElement, "src", state == null ?

                            UNKNOWN_IMG : state.booleanValue() ? CHECKED_IMG : UNCHECKED_IMG);

    }

    public Boolean getState() {

        final String img = DOM.getElementAttribute(buttonElement, "src");

        if (img.endsWith(UNCHECKED_IMG))

                        return Boolean.FALSE;

                else if (img.endsWith(UNKNOWN_IMG))

                        return null;

                else if (img.endsWith(CHECKED_IMG))

                        return Boolean.TRUE;

                else

                        throw new IllegalArgumentException("unknown checkbox state");

    }

    @Override

        public Boolean getValue() {

        return value;

    }

    @Override

        public void setValue(final Boolean _value) {

        value = _value;

    }

    @Override

        public HandlerRegistration addValueChangeHandler(

            ValueChangeHandler<Boolean> handler) {

            // Is this the first value change handler? If so, time to add handlers

            if (!valueChangeHandlerInitialized) {

                    ensureDomEventHandlers();

                    valueChangeHandlerInitialized = true;

            }

            return addHandler(handler, ValueChangeEvent.getType());

          }

    protected void ensureDomEventHandlers() {

        addClickHandler(new ClickHandler() {

                @Override

                        public void onClick(ClickEvent event) {

                        ValueChangeEvent.fire(TristateCheckBox.this, getValue());

                }

        });

    }

    @Override

        public void setValue(Boolean _value, boolean fireEvents) {

        Boolean oldValue = getValue();

        setValue(_value);

        if (_value.equals(oldValue))

                        return;

        if (fireEvents)

                        ValueChangeEvent.fire(this, _value);

    }

}