tapestry-framework/src/org/apache/tapestry/components/Foreach.java

//  Copyright 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.tapestry.components;

import java.util.Iterator;

import org.apache.tapestry.AbstractComponent;
import org.apache.tapestry.IBinding;
import org.apache.tapestry.IMarkupWriter;
import org.apache.tapestry.IRequestCycle;
import org.apache.tapestry.Tapestry;

/**
 *  Repeatedly renders its wrapped contents while iterating through
 *  a list of values.
 *
 *  [<a href="../../../../../ComponentReference/Foreach.html">Component Reference</a>]
 *
 *  <p>
 *  While the component is rendering, the property
 *  {@link #getValue() value} (accessed as
 *  <code>components.<i>foreach</i>.value</code>
 *  is set to each successive value from the source,
 *  and the property
 *  {@link #getIndex() index} is set to each successive index
 *  into the source (starting with zero).
 * 
 *  @author Howard Lewis Ship
 *  @version $Id$
 * 
 **/

public abstract class Foreach extends AbstractComponent
{
    private Object _value;
    private int _index;
    private boolean _rendering;

    public abstract IBinding getIndexBinding();


    /**
     *  Gets the source binding and returns an {@link Iterator}
     *  representing
     *  the values identified by the source.  Returns an empty {@link Iterator}
     *  if the binding, or the binding value, is null.
     *
     *  <p>Invokes {@link Tapestry#coerceToIterator(Object)} to perform
     *  the actual conversion.
     *
     **/

    protected Iterator getSourceData()
    {
    	Object source = getSource();
    	
 		if (source == null)
 			return null;
 		
        return Tapestry.coerceToIterator(source);
    }

    public abstract IBinding getValueBinding();

    /**
     *  Gets the source binding and iterates through
     *  its values.  For each, it updates the value binding and render's its wrapped elements.
     *
     **/

    protected void renderComponent(IMarkupWriter writer, IRequestCycle cycle)
    {
        Iterator dataSource = getSourceData();

        // The dataSource was either not convertable, or was empty.

        if (dataSource == null)
            return;


        try
        {
            _rendering = true;
            _value = null;
            _index = 0;
            
            IBinding indexBinding = getIndexBinding();
            IBinding valueBinding = getValueBinding();
            String element = getElement();

            boolean hasNext = dataSource.hasNext();

            while (hasNext)
            {
                _value = dataSource.next();
                hasNext = dataSource.hasNext();

                if (indexBinding != null)
                    indexBinding.setInt(_index);

                if (valueBinding != null)
                    valueBinding.setObject(_value);

                if (element != null)
                {
                    writer.begin(element);
                    renderInformalParameters(writer, cycle);
                }

                renderBody(writer, cycle);

                if (element != null)
                    writer.end();

                _index++;
            }
        }
        finally
        {
            _value = null;
            _rendering = false;
        }
    }

    /**
     *  Returns the most recent value extracted from the source parameter.
     *
     *  @throws org.apache.tapestry.ApplicationRuntimeException if the Foreach is not currently rendering.
     *
     **/

    public Object getValue()
    {
        if (!_rendering)
            throw Tapestry.createRenderOnlyPropertyException(this, "value");
  
        return _value;
    }

    public abstract String getElement();

    public abstract Object getSource();

    /**
     *  The index number, within the {@link #getSource() source}, of the
     *  the current value.
     * 
     *  @throws org.apache.tapestry.ApplicationRuntimeException if the Foreach is not currently rendering.
     *
     *  @since 2.2
     * 
     **/
    
    public int getIndex()
    {
        if (!_rendering)
            throw Tapestry.createRenderOnlyPropertyException(this, "index");
        
        return _index;
    }

}