    001// Copyright 2009, 2010 The Apache Software Foundation
    002//
    003// Licensed under the Apache License, Version 2.0 (the "License");
    004// you may not use this file except in compliance with the License.
    005// You may obtain a copy of the License at
    006//
    007// http://www.apache.org/licenses/LICENSE-2.0
    008//
    009// Unless required by applicable law or agreed to in writing, software
    010// distributed under the License is distributed on an "AS IS" BASIS,
    011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012// See the License for the specific language governing permissions and
    013// limitations under the License.
    014
    015package org.apache.tapestry5.corelib.internal;
    016
    017import org.apache.tapestry5.MarkupWriter;
    018import org.apache.tapestry5.MarkupWriterListener;
    019import org.apache.tapestry5.dom.Element;
    020import org.apache.tapestry5.ioc.internal.util.OneShotLock;
    021import org.apache.tapestry5.services.HiddenFieldLocationRules;
    022
    023/**
    024 * Used to position a hidden field (as part of a form-related component). Hidden fields are not allowed to go just
    025 * anywhere, there are rules, dictated by the (X)HTML schema, about where they are allowed. We use the
    026 * {@link org.apache.tapestry5.MarkupWriterListener} interface to monitor elements as they are started and ended to find
    027 * a
    028 * place to put content.
    029 */
    030public class HiddenFieldPositioner
    031{
    032    /**
    033     * The type of element to create.
    034     */
    035    private static final String ELEMENT = "input";
    036
    037    private final MarkupWriter writer;
    038
    039    private final HiddenFieldLocationRules rules;
    040
    041    private final OneShotLock lock = new OneShotLock();
    042
    043    private Element hiddenFieldElement;
    044
    045    private final MarkupWriterListener listener = new MarkupWriterListener()
    046    {
    047        public void elementDidStart(Element element)
    048        {
    049            if (rules.placeHiddenFieldInside(element))
    050            {
    051                hiddenFieldElement = element.element(ELEMENT);
    052                writer.removeListener(this);
    053            }
    054        }
    055
    056        public void elementDidEnd(Element element)
    057        {
    058            if (rules.placeHiddenFieldAfter(element))
    059            {
    060                hiddenFieldElement = element.getContainer().element(ELEMENT);
    061                writer.removeListener(this);
    062            }
    063        }
    064    };
    065
    066    public HiddenFieldPositioner(MarkupWriter writer, HiddenFieldLocationRules rules)
    067    {
    068        this.writer = writer;
    069        this.rules = rules;
    070
    071        this.writer.addListener(listener);
    072    }
    073
    074    /**
    075     * Returns the hidden field element, which can have its attributes filled in.
    076     *
    077     * @return the element
    078     * @throws IllegalStateException
    079     *             if the element was not positioned
    080     */
    081    public Element getElement()
    082    {
    083        lock.lock();
    084
    085        // Remove the listener if it hasn't been removed already.
    086
    087        writer.removeListener(listener);
    088
    089        if (hiddenFieldElement == null)
    090            throw new IllegalStateException(
    091                    "The rendered content did not include any elements that allow for the positioning of the hidden form field's element.");
    092
    093        return hiddenFieldElement;
    094    }
    095
    096    /**
    097     * Discard this positioner (an alternative to invoking {@link #getElement()}).
    098     * If an {@link Element} has been created for the hidden field, that
    099     * element is removed.
    100     *
    101     * @since 5.2.0
    102     */
    103    public void discard()
    104    {
    105        lock.lock();
    106
    107        if (hiddenFieldElement != null)
    108            hiddenFieldElement.remove();
    109
    110        writer.removeListener(listener);
    111    }
    112
    113}