jelly-tags/swing/src/java/org/apache/commons/jelly/tags/swing/LayoutTagSupport.java

/*
 * Copyright 2002,2004 The Apache Software Foundation.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.jelly.tags.swing;

import java.awt.Component;
import java.awt.LayoutManager;

import org.apache.commons.jelly.JellyTagException;
import org.apache.commons.jelly.TagSupport;
import org.apache.commons.jelly.XMLOutput;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * An abstract base class used for concrete layout tags which create new LayoutManager implementations
 * and either export them as variables or set them on parent widgets.
 *
 * @author <a href="mailto:jstrachan@apache.org">James Strachan</a>
 * @version $Revision: 1.7 $
 */
public abstract class LayoutTagSupport extends TagSupport {

    /** The Log to which logging calls will be made. */
    private static final Log log = LogFactory.getLog(LayoutTagSupport.class);

    private String var;

    public LayoutTagSupport() {
    }

    /**
     * Adds the given layout component to the container with the specified constraints
     */
    public void addLayoutComponent(Component component, Object constraints) throws JellyTagException {
        getComponentTag().addChild(component, constraints);
    }


    // Tag interface
    //-------------------------------------------------------------------------
    public void doTag(final XMLOutput output) throws JellyTagException {

        LayoutManager layout = createLayoutManager();

        if (var != null) {
            context.setVariable(var, layout);
        }

        getComponentTag().setLayout(layout);

        // allow some nested tags to set properties
        invokeBody(output);
    }

    // Properties
    //-------------------------------------------------------------------------


    /**
     * Sets the name of the variable to use to expose the new LayoutManager object.
     * If this attribute is not set then the parent widget tag will have its
     * layout property set.
     */
    public void setVar(String var) {
        this.var = var;
    }

    // Implementation methods
    //-------------------------------------------------------------------------

    /**
     * @return the parent component tag or throw an exception
     */
    protected ComponentTag getComponentTag() throws JellyTagException {
        ComponentTag tag = (ComponentTag) findAncestorWithClass( ComponentTag.class );
        if ( tag == null ) {
            throw new JellyTagException( "This tag must be nested within a JellySwing widget tag" );
        }
        return tag;
    }

    /**
     * Factory method to create a new LayoutManager instance.
     */
    protected abstract LayoutManager createLayoutManager();
}