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Ajax4jsf is an open source extension to the JavaServer Faces standard that adds AJAX capability to JSF applications without requiring the writing of any JavaScript.
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/**
 * Licensed under the Common Development and Distribution License,
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.sun.com/cddl/
 *   
 * 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.ajax4jsf.framework.ajax;

import javax.faces.component.StateHolder;
import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.el.EvaluationException;
import javax.faces.el.PropertyNotFoundException;
import javax.faces.el.ValueBinding;

import org.ajax4jsf.framework.renderer.AjaxRendererUtils;
import org.ajax4jsf.framework.util.message.Messages;


/**
 * Inner class for build event string for parent component.
 * @author shura (latest modification by $Author: alexsmirnov $)
 * @version $Revision: 1.5 $ $Date: 2007/01/16 17:53:18 $
 * Disadvantages - not rebuild event string setted as EL expression.
 * TODO - save expressions for build event string at render phase.
 */
public class EventValueBinding extends ValueBinding implements StateHolder {
    
    /**
     * 
     */
    private static final long serialVersionUID = -6583167387542332290L;
    private String _componentId;
    
    
    /**
     * current update component. transient since saved state as component. 
     */
    transient private AjaxSupport _component = null;
    
    /**
     * Default constructor for restoreState.
     */
    public EventValueBinding() {
    	
    }

    /**
     * Constructor for build from AjaxComponent.
     * @param update
     */
    public EventValueBinding(AjaxSupport update)
    {
        _component = update;
//        _componentId = string;
    }

    /* (non-Javadoc)
     * @see javax.faces.el.ValueBinding#getType(javax.faces.context.FacesContext)
     */
    public Class getType(FacesContext facesContext) throws EvaluationException, PropertyNotFoundException
    {
        
        return String.class;
    }

    /* (non-Javadoc)
     * @see javax.faces.el.ValueBinding#getValue(javax.faces.context.FacesContext)
     */
    public Object getValue(FacesContext facesContext) throws EvaluationException, PropertyNotFoundException
    {
    	return getComponent(facesContext).getEventString();
    }
    
    private AjaxSupport getComponent(FacesContext facesContext) throws EvaluationException {

        if (_component == null)
        {
             UIComponent uiComponent = facesContext.getViewRoot().findComponent(_componentId);
            if (null != uiComponent && uiComponent instanceof AjaxComponent)
            {
                _component = (AjaxSupport) uiComponent;                    
            } else {
                throw new EvaluationException(Messages.getMessage(Messages.COMPONENT_NOT_FOUND, _componentId));
            }
            
        }

        return _component;
    }

    /**
	 * @param component the component to set
	 */
	public void setComponent(AjaxSupport component) {
		_component = component;
	}

	/* (non-Javadoc)
     * @see javax.faces.el.ValueBinding#isReadOnly(javax.faces.context.FacesContext)
     */
    public boolean isReadOnly(FacesContext facesContext) throws EvaluationException, PropertyNotFoundException
    {
        // TODO Auto-generated method stub
        return true;
    }

    /* (non-Javadoc)
     * @see javax.faces.el.ValueBinding#setValue(javax.faces.context.FacesContext, java.lang.Object)
     */
    public void setValue(FacesContext facesContext, Object value) throws EvaluationException, PropertyNotFoundException
    {
        throw new EvaluationException(Messages.getMessage(Messages.EVENT_IS_READ_ONLY));
        
    }

    /* (non-Javadoc)
     * @see javax.faces.component.StateHolder#saveState(javax.faces.context.FacesContext)
     */
    public Object saveState(FacesContext context)
    {
    	if(null == _component){
    		return _componentId;
    	} else {
    		return AjaxRendererUtils.getAbsoluteId((UIComponent) _component);
    	}
    }

    /* (non-Javadoc)
     * @see javax.faces.component.StateHolder#restoreState(javax.faces.context.FacesContext, java.lang.Object)
     */
    public void restoreState(FacesContext context, Object state)
    {
        // TODO Auto-generated method stub
        _componentId = (String)state;
    }

    /* (non-Javadoc)
     * @see javax.faces.component.StateHolder#isTransient()
     */
    public boolean isTransient()
    {
        // TODO Auto-generated method stub
        return false;
    }

    /* (non-Javadoc)
     * @see javax.faces.component.StateHolder#setTransient(boolean)
     */
    public void setTransient(boolean newTransientValue)
    {
        // TODO Auto-generated method stub
        
    }

	/* (non-Javadoc)
	 * @see javax.faces.el.ValueBinding#getExpressionString()
	 */
	public String getExpressionString() {
//		FacesContext context = FacesContext.getCurrentInstance();
//		UIComponent component = (UIComponent) getComponent(context);
//		return "#{ajaxSupport["+component.getClientId(context)+"]}";
		return null;
	}
    
}